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Infrared Spectroscopy Marianne L. McKelvy,* Thomas R. Britt, Bradley L. Davis, J. Kevin Gillie, L. Alice Lentz, Anne Leugers, Richard A. Nyquist, and Curtis L. Putzig
Analytical Sciences Laboratory, The Dow Chemical Company, Michigan Division, Midland, Michigan 48667 Review Contents Overview of Analytical Infrared Spectroscopy Books Reviews Far-IR Techniques and Applications On-Line and In-Process Applications of Infrared Spectroscopy In Situ and Real-Time Analysis In Situ and Real-Time Infrared Analysis of Films and Surfaces In Situ Electrochemical Studies In Situ Studies of Catalysis General Applications of In Situ IR Monitoring of Chemical Processes Environmental Analysis Atmospheric Chemistry Remote Monitoring Open-Path Monitoring Environmental Monitoring Food and Agriculture Coal and Carbon High Carbon Black-Loaded Samples Coal Analysis Diamond-Like Carbon Films Analysis of C60/C70 Fullerenes Biochemical Applications Surface Techniques and Applications Single Crystals and Other Low Surface Area Materials Semiconductors, Langmuir -Blodgett Films, and Self-Assembled Films Catalysts and Other High Surface Area Materials Polymer Applications Quantitative Analysis Attenuated Total Reflectance Photoacoustic Spectroscopy Diffuse Reflectance Spectroscopy Time-Resolved Infrared Spectroscopy Infrared Microscopy Hyphenated Techniques Matrix Isolation Spectroscopy GC/FT-IR LC/FT-IR, GPC/FT-IR, FIA/FT-IR, TLC/FT-IR SFC/FT-IR TGA/FT-IR Spectral Libraries, Searching, Computer-Assisted Interpretation, Artificial Intelligence, and Data Transfer Theoretical Studies, Band Intensities, Vibrational Assignments, Temperature Effects, and Pressure Effects Group Frequencies, Solute/Solution Studies, Spectra/ Structure Correlations, and Qualitative Practices Miscellaneous IR Techniques Literature Cited
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This review covers the published literature for the period November 1993 to October 1995 on aspects of infrared spectrosS0003-2700(96)00003-0 CCC: $25.00
© 1996 American Chemical Society
copy that are relevant to chemical analysis. Our review is directed to papers written in English or in certain aspects of IR spectroscopy that are of particular interest to one or more of the co-authors. Where some overlap may occur in a particular area, a few selected references to Raman or FT-Raman spectroscopy are included. OVERVIEW OF ANALYTICAL INFRARED SPECTROSCOPY Infrared radiation is commonly defined as electromagnetic radiation with frequencies between 14 300 and 20 cm-1 (0.7 and 500 µm). When a normal molecular motion such as a vibration, rotation, rotation/vibration or lattice mode, or combination, difference, or overtone of these normal vibrations results in a change in the molecule’s dipole moment, a molecule absorbs infrared radiation in this region of the electromagnetic spectrum. The corresponding frequencies and intensities of these infrared bands, the infrared spectrum, may be used to characterize the material. Infrared spectral information may be used to identify the presence and amount of a particular compound in a mixture. Different classes of chemical compounds contain structural units that absorb infrared radiation at essential similar frequencies and intensities within that class of compound. These bands are called “group frequencies”. The infrared spectroscopist uses knowledge of these group frequencies to predict the structures of unknown molecules when standard infrared spectra are not available. Sample collection and presentation accessories exist which allow the analyst to collect spectra as solids, liquids, vapors, and in solution, at various temperatures, and while undergoing mechanical deformation. Experiments conducted under such conditions assist the spectroscopist in the determination of the structures of molecules in different phases as well as structure/ property relationships of materials. Modern instrumentation allows the collection of infrared spectra of materials at low-picogram levels. The ability of infrared spectroscopy to examine and identify materials under such a wide variety of conditions has earned this technique the premier position as the “workhorse” of analytical science. BOOKS Socrates authored the second edition of Infrared Characteristic Group Frequencies (A1). Roeges authored a guide to the complete interpretation of IR spectra of organic structures (A2). Coleman edited a book on practical sampling techniques for IR analysis (A3). Lau et al. edited a book on time-resolved vibrational spectroscopy (A4). Bertie and Wieser edited the book on the proceedings of the 9th international conference on FT-IR spectroscopy (A5). Andresen and Shepherd edited a book on IR optical imaging device technology (A6). Van der Veken and Barnes edited a book on the vibrational and rotational spectroscopic properties of molecules (A7). Dawson and Appebaum edited on book on IR detector materials and devices (A8). Analytical Chemistry, Vol. 68, No. 12, June 15, 1996 93R
Holst edited a book on IR imaging systems (A9). Scholl edited a book on IR space-borne remote sensing (A10). Dereniak and Sampson edited a book on IR detectors and focal plane arrays (A11). Epchtein et al. edited a book on science with astronomical near-IR sky surveys (A12). Bernhard and Grosjean have written about the IR spectra of carotenoids (A13). Schrader edited a book on methods and applications using IR and Raman spectroscopy (A14). Radpour and McCrary have edited a book on long-wavelength IR detectors and arrays (A15). Urban and Provder have edited a book on the multidimensional spectroscopy of polymers (A16). Smith authored a book covering the fundamentals of FT-IR spectroscopy (A17). Fowler edited a book covering IR detectors and instrumentation for astronomy (A18). REVIEWS Coleman has reviewed theoretical considerations of sample handling techniques for IR spectroscopy (B1). Perkins has defined sample handling techniques for obtaining a good IR spectrum of a sample in any physical phase and also discusses computer data processing (B2). Lang and Richwine reviewed the versatile sampling methods of IR microspectroscopy (B3). McClure reviewed sample preparation for IR hyphenated techniques with emphasis on GC/FT-IR (B4). Compton and Compton reviewed possible pitfalls while performing quantitative IR analyses (B5). Williams reviewed spectral artifacts caused by improper sample preparation, which then causes errors in spectral interpretation (B6). Russell and Fraser have reviewed the application of IR spectroscopy to clay mineralogy studies (B7). Leopold et al. have reviewed current themes in microwave and IR spectroscopy of weakly bound complexes (B8). Ribnikar has reviewed the consequences of anharmonicity, resonance, and intermolecular interaction on the IR spectrum of a substance (B9). Owrutsky et al. have discussed recent experimental and theoretical studies of vibrational relaxation of relatively small molecules in solution (B10). Levine has discussed FT-IR remote sensing for monitoring airborne gas and vapor contaminants in the atmosphere (B11). Gunson has reviewed the ATLAS 1 experiment for the analysis of trace molecules in the atmosphere (B12). Lee et al. have reviewed the application of IR for indoor air monitoring (B13). Yu and Phillips have discussed the relative advantages and disadvantages of various IR techniques for identifying and measuring dilute multicomponent mixtures in bioreactors (B14). Marcott et al. have reviewed dynamic two-dimensional IR spectroscopy for the characterization of polymers and polymer blends (B15). Shaw and Mantsch have reviewed the development of two-dimensional IR spectroscopy with emphasis on the experimental conditions that are required to produce quality twodimensional IR spectra (B16). Dhar et al. reviewed time-resolved vibrational spectroscopy in the impulsive limit (B17). Szafran and Dega-Szafran have written a critical review the isotope effect (D for H) in IR spectra (B18). Almond and Orrin have reviewed the field of matrix isolation (MI) and concluded that MI FT-IR is the mainstay for these experiments (B19). Fontana et al. have reviewed the application of Raman and IR to the study of molecular dynamics in liquid crystal polymers (B20). 94R
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Lee has reviewed and compared the applications of mid- and near-IR in the analysis of fibers, films, coatings, and biopolymers (B21). Haris and Chapman have discussed the analysis of polypeptide and protein structures using FT-IR (B22). Chalmers and Everall have discussed the complementary role of Raman and IR spectroscopy in polymer characterization (B23). Ozin has discussed in situ chemistry using FT-IR by use of zeolites as a catalyst (B24). Coffey and Mankin have reviewed FT-IR for stratospheric research (B25). Fishman et al. reviewed vibrational spectroscopic approaches to conformational equilibrium and kinetics in the condensed phase (B26). Potts and Francoeur have discussed the utilization of IR to study stratum corneum lipids in vitro (B27). Newman has reviewed the application of IF and Raman spectroscopy to study defects and impurities in group 111A pnictides (B28). Coudurier and Lefebvre reviewed the use of IR for the characterization of catalysts (B29). Faix has reviewed the literature on the characterization of lignin using IR spectroscopy (B30). Treado and Morris have reviewed the application of IR and Raman in imaging applications (B31). Fontana has discussed the use of vibrational spectroscopy to study molecular reorientation dynamics in liquid crystal mesophases with emphasis on the temperature dependence as the nematic/isotropic phase transition is approached (B32). Lisy has reviewed the application of vibrational spectroscopy in the study of cluster of cluster ions (B33). Davidson has reviewed the literature on the utilization of vibrational spectroscopy to study coordinated ligands (B34). Katon has discussed the application of IR and Raman microspectroscopy in the study of chemistry (B35). Saykally discussed the application of tunable lasers for infrared laser spectroscopy of cluster complexes using Schottky mixers (B36). Davidson reviewed the literature on the vibrational spectra of transition element compounds and main-group element compounds (B37, B38). Kalasinsky et al. discussed the application of FT-IR techniques for the analysis of drugs of abuse (B39). Kalasinsky and Kalasinsky reviewed sampling techniques for IR analysis in the environment and forensic laboratories (B40). Kalasinsky et al. discussed the application and comparison of IR and MS for drug analysis (B41). Tascon et al. reviewed IR and temperature-programmed desorption of perovskite surfaces (B42). Seitz reviewed analytical spectroscopy with IR transmitting optical fibers (B43). Zecchina and Arean reviewed IR studies of surface species obtained by interaction of organometallic compounds with oxidic surfaces (B44). Comyn discussed contact angle measurement, surface IR spectroscopy, X-ray photoelectron spectroscopy (XPS), and static SIMS of polymers (B45). Allara summarized the critical issues for application of IR to characterization of surface processing (B46). Dumas discussed recent aspects of surface IR spectroscopy including synchrotron IR radiation as a source of high brightness in the far-IR region (B47). McClelland compiled a practical guide to FT-IR photoacoustic spectroscopy (B48). Ibach discussed the vibrational spectroscopy of surfaces using electron energy loss spectroscopy (B49). Somorjai reviewed the frontiers of surface structure analysis including HREELS to determine the vibrational spectra of atoms and molecules at surfaces (B50). Martin discussed recent advances in near-IR reflectance spectroscopy (B51). McClure also reviewed near-IR spectroscopy
(B52). Lin and Brown discussed novel applications of near-IR spectroscopy of water and aqueous solutions from physical chemistry to analytical chemistry (B53). Putzig et al. reviewed IR spectroscopy for the period late 1991 to October 1993 (B54). Ridgway has reviewed visible and IR imaging interferometry from space (B55). Faix reviewed FT-IR of lignin in solution (B56). Treado and Morris reviewed IR and Raman imaging (B57). Jacox reviewed the shifts in the ground-state vibrational fundamental frequencies of diatomic and small polyatomic free radicals, molecular ions, and other short-lived molecules trapped in neon and argon matrixes (B58). Yamamoto and Ishida reviewed optical theory as applied to IR spectroscopy (B59). Hollins reviewed the application of reflection/absorption IR spectroscopy to extended metal and semiconductor surfaces (B60). Meier reviewed the field of two-dimensional IR spectroscopy for the characterization of polymers (B61). Polavarapu discussed the application of circular dichroism FT-IR in the determination of the absolute configuration of drugs (B62). Giangiacomo and Nzabonimpa reviewed the utilization of near-IR in the dairy industry (B63). Kearley reviewed the application of inelastic neutron scattering (INS) for the study of molecular vibrations (B64). Workman reviewed near-IR process analyses for the period 1980-1994 (B65). Dittmar et al. reviewed the principles and application of FT-photoacoustic IR spectroscopy to polymers and related materials (B66). Yoshida and Matsuura reviewed the conformational analysis of materials containing the poly(oxyethylene) chain by application of IR and Raman spectroscopy (B67). Zerbi reviewed the applications of vibrational spectroscopy in the studies of the electronic structure of conjugated polymers (B68). Bershtein and Ryzhov reviewed the application of far-IR studies of polymers. These studies show that this is an important tool for characterizing the molecular dynamics and intermolecular interactions in polymers which to a considerable extent describe the physical properties of the polymer (B69). Mozayeni reviewed the application of FT-IR and NMR for the identification and quantitation of cationic surfactants (B70). Howdle and Poliakoff reviewed the development of a range of cells suitable for the analysis of supercritical fluids by application of IR, Raman, and UV/visible spectroscopy (B71). Wilson et al. reviewed the application of FT-IR for on-line quality and process control (B72). Adams et al. reviewed the application of surface analysis of thick polymer films using internal reflection FT-IR. Surfaces studied ranged from 5 nm to several hundred nanometers (B73). Urban reviewed recent advances in photoacoustic FT-IR in the study of cross-linking of thermoseting polymers, adhesion failure, and interfacial interactions (B74). Urban reviewed the principles and applications of FT-IR and Raman spectroscopy in polymer analyses (B75). Siesler reviewed the improvements in rapidscanning FT-IR and FT-Raman spectroscopy which aid in the chemical and physical studies of polymers (B76). Kamaras et al. reviewed the possibilities and limitations of the use of far-IR ellipsometry for the determination of the far-IR dielectric function of high-temperature superconductors (B77). Gunapala et al. discussed the application of gallium arsenide-based detectors at very long-IR wavelengths (B78). Sargent and Koenig reviewed the application of IR spectroscopy for the study of polymer blend compatibility on the molecular level (B79).
Mitchell reviewed the fundamentals and applications of diffuse reflectance FT-IR in the investigation of polymer surfaces and structures of films and fibers (B80). Speight reviewed the techniques useful in the structural analysis of petroleum (B81). Blitz and Augustine reviewed the application of diffuse reflectance FT-IR in the study of heterogeneous catalysts (B82). Coleman and Gordon reviewed the application of GC/matrix isolation-FT-IR in the analysis of natural products (B83). Garrell reviewed the synergy of computational chemistry and spectroscopy in understanding molecular structure and dynamics at interfaces (B84). McClure reviewed the discovery, application chemometrics, and industrial application of near-IR spectroscopy (B85). Wilson and Goodfellow reviewed the application of IR spectroscopy in the analysis of food (B86). Amar et al. reviewed the IR spectroscopy of solvated molecules (B87). Crofton et al. reviewed the IR spectroscopy of hydrogenbonded charged clusters (B88). Davidson reviewed the IR and Raman spectroscopy of compounds of main group elements (B89), transition element compounds (B90), and coordinated ligands (B91). Peters has discussed the on-line applications of FT-IR process monitors in the production of pharmaceuticals, specialty chemicals, polymers, and refinery products (B92). Korzeniewski and Severson have reviewed the applications of IR spectroscopy in the study of catalytic reactions and related absorption phenomena on single-crystal electrodes (B93). Lachenal has reviewed the application of near-IR in the analysis of polymeric materials (B94). Taylor and Jordan reviewed the application of supercritical fluid extraction (SFE) coupled with FT-IR for the analyses of textile fiber finishes (B95). Fina reviewed the field of depth profiling of polymer surfaces utilizing FT-IR for study of the discrete and continuous change in the concentration and chemical structure near the surface of polymer materials (B96). Siebert reviewed the applications of FT-IR in the study of biochemical and biological problems (B97). Middaugh et al. reviewed IR spectroscopy in the study of protein folding (B98). Jackson et al. has reviewed the use and misuse of FT-IR in the determination of protein structure (B99). Zotti has reviewed the application of electrochemistry and IR to conducting polymers (B100). Chalmers and Everall have reviewed the role of vibrational spectroscopy/microscopy techniques in polymer characterization (B101). Smith et al. have reviewed the techniques for the characterization and analysis of rubbers and synthetic polymers, copolymers, and blends (B102). Wlodarczak has reviewed the application of IR spectroscopy in the field of astrochemistry (B103). LeDoucen and Boulet reviewed methods to determine IR band shapes of data obtained remotely from materials in the atmosphere (B104). Bobin and Moret-Bailly have reviewed the field of vibration/rotation FT-IR spectroscopy for spherical top molecules (B105). Flaud and Perrin have reviewed the application of FT-IR in the study of asymmetric top molecules (B106). Russwarm and Childers have reviewed the application of FT-IR in the analysis of materials in the vapor phase at the ppb level (B107). Connes has reviewed the historical account of the development of high-resolution astronomical and laboratory FT-IR spectrometry under the leadership of Jacquinot over the period 1964-1974 (B108). Korzeniewski and Severson have reviewed the applications of FT-IR in the study of catalytic reactions and related Analytical Chemistry, Vol. 68, No. 12, June 15, 1996
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adsorption phenomena on single-crystal electrodes (B109). Barnes has reviewed the techniques and applications of matrix isolation in air analyses (B110). Scheirs and Carlsson have reviewed IR, NMR, and colorimetric methods for detecting and characterizing hydroperoxide groups in oxidized polyolefins (B111). Wilks has reviewed and discussed potential IR applications of the region between 2 and 5 µm in the analysis of materials (B112). Man and Pan have reviewed the theoretical investigation of p-type IR detectors (B113). Pireaux has reviewed the application of electron-induced vibrational spectroscopy (H REELS) of polymer surfaces (B114). Helm has reviewed the utilization of IR in the analysis of semiconductor superlattices (B115). Nafie has reviewed the circular polarization IR spectroscopy of chiral molecules (B116). Quack has reviewed his recent work of rovibrational motion of molecules using IR spectroscopy (B117). Bulanin has reviewed the spectroscopy of molecules in liquid noble gases (B118). Crofton et al. have reviewed the study of hydrogen-bonded charged clusters using IR spectroscopy (B119). Moortgat and Griffith have reviewed the technique of cryogenic grab sampling associated with matrix isolation FT-IR (B120). Klaeboe has reviewed methods for studying molecular conformers by utilization of IR and Raman spectroscopy (B121). Sheppard reviewed the vibrational spectroscopic contributions to chemisorption and catalysis (B122). Turner et al. reviewed the recent advances in kinetic IR spectroscopy (B123). Goormaghtigh et al. reviewed the field of membrane protein structure determination utilizing FT-IR (B124). Clarke reviewed the application of IR in the analysis of detergents (B125). Spells reviewed the potential of techniques based on isotopic substitution, in particular mixed-crystal IR spectroscopy in the analysis of chain conformation and folding in polyethylene crystals (B126). Van Alsten has reviewed the application of attenuated total reflectance (ATR) FT-IR for measurement of macromolecule diffusion in situ over a wide range of diffusion coefficients and temperatures (B127). Walker and Hochstrasser have reviewed the methods, theory, and applications of ultrafast vibrational spectroscopy (B128). Mathies has discussed the application of vibrational spectroscopy in the analysis of bacteriorhodopsin (B129). Naumann et al. have discussed the identification and characterization of microorganisms by the utilization of FT-IR (B130). Sander and Kirschfeld have discussed the spectra of matrixisolated compounds containing strained three-membered ring systems (B131). Griffiths and Urban have reviewed the application of IR and Raman spectroscopies in polymer analysis (B132). Palmer et al. have discussed step-scan FT-IR studies of polymers and liquid crystals (B133). Fina has reviewed the results of IR analyses of Nylon 11 (B134). Bain has reviewed the field of sum-frequency spectroscopy (SFS), a nonlinear optical technique that yields vibrational spectra of molecules at interfaces (B135). Poliakoff et al. have reviewed the application of vibrational spectroscopy in supercritical fluids for polymer analysis (B136). Ryczkowski reviewed the application of IR for the analysis of N2O (B137). Doyle has compared the utilization of mid-IR and near-IR application in process analysis (B138). Xin and Gao have reviewed the developments of in situ molecular spectroscopy in the study of the active phases of 96R
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catalysts (B139). Bellini et al. have discussed the progress in far-IR precision spectroscopy (B140). Ciura have discussed the application of lasers useful in the far-IR region (B141). Chang and Wang have discussed the application of near-IR in monitoring polymer polymerization reactions (B142). FAR-IR TECHNIQUES AND APPLICATIONS Far-IR spectroscopy, because of its sensitivity to threedimensional order, continues to be utilized primarily as a tool to gain information regarding the physical structure of solid materials and geometry of molecules and macromolecules. Far-IR spectroscopy of condensed media, including topics on far-IR of liquids, nitro compounds, and liquid crystals, lowfrequency Raman spectroscopy, and latticelike models, was reviewed (C1). A method was discussed for the absolute determination of complex reflectivity in terms of far-IR reflection standards (C2). The development of a far-IR interferometer was described which allows dispersive Fourier transform spectroscopy to be performed in the reflection mode (C3). The far-IR spectra of chloromethyl methyl ether and three of the deuterium isotopomers were recorded, vibrational assignments were made, the barrier to internal rotation was estimated, and comparison to ab initio calculations were made (C4). The far-IR rotational spectra of deuterated methane were used to derive a dipole moment function (C5, C6). Far-IR and Raman spectra of pyridine derivatives at varying temperatures were used to monitor structural phase transitions and determine the nature of the intermolecular interactions (C7). Far-IR and Raman spectra of 1,3-dioxole and 4H-pyran were analyzed and contrasted with molecular mechanics calculations results predicting puckered and planar structures (C8, C9). Assignments were made of lowfrequency IR and Raman spectra of oxygen-bridged copper cluster complexes to deduce the structure of the metallic core (C10). The temperature dependence of far-IR reflection/absorption spectra of thin poly(ethylene oxide) films was used to study structural changes of the crystalline polymers (C11). Far-IR spectra of benzene-fluorinated benzene binary mixtures were contrasted with spectra of the neat liquids to show evidence of a short-lived complex (C12). Far-IR, low-frequency Raman, and phonon dispersion curves were used in a lattice dynamic study of 4-nitropyridine N-oxide and its deuterated derivative (C13). A far-IR reflectivity study of double-chain yttrium barium copper oxide superconductors was made from 10 to 300 K, showing changes in the phonon parameters hold similarly to the single-chain material (C14). A study of barium rare earth cuprate superconductors was done using temperature-dependent far-IR reflectivity (C15). Lattice dynamics calculations and far-IR spectra of lanthanide superconductors were studied (C16). Far-IR reflectivitiy of ceramic superconductors was used to show the effects of yttrium replacement on phonon-mode strength and critical temperature (C17). Techniques useful for obtaining far-IR transmission spectra of high-Tc superconductors and related synthetic precursors were discussed (C18). Evidence of polaron formation in superconducting cuprates was shown by far-IR reflectivity spectra (C19). The electron/phonon interaction and phase transition in layered indium sulfide selenide crystals was studied by far-IR (C20). Far-IR reflection spectra of barium lanthanide cuprates were used as evidence of phase separation in the samples (C21). The temperature dependence of lattice vibration spectra for mercury zinc tellurides was
measured at 90-295 K (C22). Far-IR transmission and reflection spectra of Rochelle salt together with Raman spectra were obtained in the temperature range between 15 and 300 K to determine soft-mode behavior (C23). The vibrational spectra of cadmium gallium sulfide solid solutions were studied by far-IR and Raman spectroscopies (C24). The application of far-IR and Raman spectroscopies to the analysis of zinc selenide sulfide layers was discussed (C25). Far-IR and Raman transmission spectra of silver tantalum iodide selenides were studied (C26). Raman and far-IR spectra of antimony germanium sulfide amorphous semiconductors were used to determine the local structure around the antimony atom (C27). Raman and far-IR spectra of betaine-calcium chloride dihydrate were investigated under hydrostatic pressure at various temperatures (C28). Polarized far-IR and Raman spectra of copper metagermanate single crystals were studied and band assignments made (C29, C30). Far-IR reflectivity data were used to study lattice modes of gallium telluride crystals (C31). A study of impurity-induced phonon disordering in cadmium zinc telluride alloys was done using far-IR reflectivity and Raman spectroscopies (C32). The temperature-dependent far-IR spectrum of liquid water was studied using a technique based on ultrashort electromagnetic pulses which is useful for highly absorbing liquids (C33). Far-IR reflectivity spectra of hydrogen-bonded ferroelectric potassium dihydrogen phosphate were measured using synchrotron radiation (C34). The quality of an ultrathin gallium indium arsenide superlattice was monitored by use of polarized far-IR reflectivity measurements (C35). A thesis reported the far-IR reflection/ absorption spectra of amorphous and polycrystalline gallium arsenide films (C36). Far-IR spectra of mercury cadmium manganese tellurides were obtained at 90 and 300 K (C37); defect and clustering modes of single crystals of these compounds were studied (C38). The low-energy magnetooptical properties of chromium mercury selenide was studied by far-IR spectroscopy in high magnetic fields (C39). Dipole-forbidden vibrational modes for NO and CO on copper were observed by far-IR reflectivity spectroscopy (C40). The far-IR reflection spectra of sillenite crystals and their solid solutions were measured and interpreted (C41). Far-IR reflectivity spectra of two isomorphous ferroelectric compounds were studied in the temperature range 90-330 K (C42). Far-IR reflection spectra of dielectric ceramics and some perovskites were measured at room temperature to investigate the effect of the crystal structure on the dielectric properties (C43). The interface composition in superlattices was assessed using far-IR reflectivity spectroscopy (C44). Far-IR absorption and reflection spectra of arsenic sulfide glass were measured at room temperature (C45). A balloon-borne far-IR spectrometer was used to obtain thermal emission spectra of HCl and HF in the atmosphere from 15 to 50 km. Vertical profiles for both compounds were derived for the period from 1983 to 1990 (C46). ON-LINE AND IN-PROCESS APPLICATIONS OF INFRARED SPECTROSCOPY A system for sorting waste plastics using near-IR reflectance spectra and neural networks has been developed at Sandia National Laboratories. Initial work has been successful in classifying near-IR spectra into five or six resin categories (D1). NearIR transmission spectroscopy combined with multivariate analysis was used in a single-screw extruder to monitor the concentration
of titanium dioxide, a white inorganic filler in molten poly(ethylene terephthalate) (D2). The potential of near-IR diffuse reflectance spectroscopy for quality control of the manufacturing process for a solid pharmaceutical preparation was investigated. Two approaches, a fiber-optic assembly and a spinning cell, were evaluated for the measurement (D3). An FT-IR spectrometer having a long absorbing path in an open-field mode was applied to the measurement of air quality in a semiconductor processing facility. The instrument was demonstrated to be a suitable instrument for the analysis of solvent vapors from the process (D4). A field study was performed to evaluate the relative merits of open-path FT-IR spectroscopy and various gas chromatographic approaches for the determination of organic vapors within operating process areas (D5). A noninvasive near-IR reflectance analysis method was developed to confirm the identity of blister-packed, film-coated, and non-film-coated tablets for clinical trial supplies (D6). The use of near-IR spectroscopy for the detection of particulates in recycled HDPE prior to extrusion was described. The method was successful in obtaining particle size distributions (D7). A nearIR spectrometer was interfaced directly to a polyurethane reactor with a fiber-optic immersion probe in order to quantify the isocyanate levels in the reaction mixture (D8). Near-IR reflectance spectroscopy was used to determine various physical characteristics of primary materials currently used in the pharmaceutical industry (D9). The possibility of applying near-IR reflectance spectroscopy to the integrated control of the production cycle of cefuroxime axetil tablets was investigated (D10). Near-IR spectra of Precambrian metagraywacke in the Black Hills, SD, demonstrate that reflectance spectroscopy can be used to monitor metamorphic grade (D11). A near-IR advanced control system has been controlling the gasoline blender at BP France’s Lavera refinery for more than two years (D12). Short-wavelength near-IR spectroscopy in the wavelength range 700-1100 nm was used to monitor cell density in a fermentation process (D13). The combination of a pattern recognition technique with near-IR spectroscopy to determine the conformity of a pharmaceutical mixture could be used in the routine checking of a pharmaceutical process (D14). By use of near-IR instrumentation designed specifically for the process environment, the isocyanate content of a urethane polymerization reaction was monitored in real time (D15). Results of monitoring polystyrenepoly(oxyphenylene) melt blends with near-IR spectroscopy using new fiber-optic probes and flow cell, robust calibration models, and faster multivariate routines were described (D16). Developments produced a single optical fiber probe designed for the chemical process industry which can be used directly in a feedstock stream (D17). A system for continuous in-line near-IR monitoring of molten polymer blends, copolymers, and polymer reactions was developed (D18). Stack gases of wood- and oilburning boilers operating at the Technological Research Center of Finland were analyzed by a commercial FT-IR gas analyzer system (D19). Sulfasalazine was determined by near-IR spectroscopy and multivariate analysis in reflectance mode with a fiber-optic probe (D20). A qualitative nondestructive technique for the identification of fibers was developed using near-IR spectroscopy and neural networks (D21). The difficulties encountered during an attempt to set up an on-line continuous near-IR measurement of sugar and solids in sugar syrups were discussed (D22). Tests of transient Analytical Chemistry, Vol. 68, No. 12, June 15, 1996
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IR spectroscopy as a monitor of cure levels of both coatings and bulk solid materials on the pilot or production lines of three different manufacturers were reported (D23). Applications of FTIR spectrometers at BASF for process monitoring were described, including spectrometer design, servicing, and operational aspects (D24). Near-IR transmission spectra recorded from poly(ethylene terephthalate) melt contained sufficient information to estimate the number of carboxylic end groups and the relative viscosity (D25). In response to industry need, a Cooperative Research and Development Agreement was established between the National Institute of Standards and Technology and Morton International Advanced Materials, to study the application of FT-IR spectroscopy to perform real-time, in situ quantitation of metal organic constituents in a multicomponent feed stream to chemical vapor deposition (CVD) reactors (D26). A technique for the on-line analysis of hydrophobic compounds in water or air combining IR absorption measurements and continuous extraction in one step was developed (D27). FT-IR spectroscopy was evaluated as a nonintrusive probe of CO and CO2 concentrations and average line-of-sight temperature and temperature profiles on a 500-kW oil-fired combustion test facility (D28). A computer algorithm, which matches the theoretical to measured IR reflectance spectra, was successfully employed to determine multiple thin-film properties of integrated circuits (D29). The development and application of an on-line process near-IR system that can be used to control gasoline blending, diesel fuel blending, and/or catalytic re-forming was discussed (D30). Open-path FT-IR spectroscopy was used to monitor workplace gas and vapor exposures and emissions from hazardous waste sites and to track emissions along fence lines (D31). In situ FT-IR absorption spectroscopy was used as a diagnostic tool to evaluate the gas phase above a heterogeneous reaction, black liquor char combustion (D32). The methodology and benefits of utilizing near-IR on-line spectroscopy to monitor a polyol reaction were discussed (D33). An algorithm has been developed for the detection of gaseous pollutants/chemical agents with single- or multiple-peak spectra using signal-processing techniques on FT-IR interferograms (D34). An electrothermal fountain was used to heat gas-phase samples at 300-400 °C to observe their near-IR emissions (D35). A nearIR instrument leased from Tecator, using single-strand fiber optics was set up in a brewing process environment and tested for its ability to measure in-line (D36). During an on-line test period, a prototype of the Bran+Luebbe InfraPrime System was used to generate calibration models for motor octane number in gasoline and to predict results for a continuous sample stream (D37). The on-line detection and identification of unexpected interferents in multivariate predictions of organic gases using FT-IR spectroscopy was discussed (D38). Fiber-optic-based FT-IR spectroscopy was demonstrated as a technique for remote in situ monitoring of concentration levels of organometallic species in gas delivery lines to metal-organic vapor phase epitaxy systems (D39). Seven hydrocarbons were determined continuously in gasoline engine exhaust over the U.S. Federal Test Procedure cycle using FT-IR spectroscopy (D40). Continuous in-line measurement of alcohol, extract, and calories helped improve the accuracy of blending high-gravity beer to specified targets (D41). A vent analyzer, based on an IR filter photometer, was developed which was required to monitor two components, ethane and ethylene, every 30 s in a multicomponent vent from an 98R
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absorption process (D42). A near-IR spectroscopy technique for the control of a lactic acid fermentation process has been proposed. Lactic acid, glucose, and biomass concentrations were determined by the near-IR spectroscopy method (D43). A nearIR camera was installed in an experimental setup for real-time plastic identification. The resulting images were processed in two different ways for rapid classification: singular value decomposition (D44) and multivariate image rank analysis (D45). ATR FTIR spectroscopy applied to the determination of individual sugar concentrations in real mixtures produced during starch hydrolysis gave acceptable results for the analysis of glucose and maltose but not for maltotriose or maltodextrins (D46). Ashland Petroleum Co. successfully used a near-IR process analyzer in closedloop feedback control at its St. Paul Park, MN refinery for the real-time determination of octane number (D47). Mass-transfer coefficients and equilibrium solubilities for the systems R-tocopherol-CO2, isophytol-CO2, and dihydroisophytol-CO2 were determined in the temperature range from 327 to 353 K and pressures up to 35 MPa by on-line near-IR spectroscopy (D48). IN SITU AND REAL-TIME ANALYSIS In Situ and Real-Time Infrared Analysis of Films and Surfaces. An instrument was developed to acquire polarized ATR IR spectra of supported monomolecular films in situ at the lipid/water interface (E1). An FT-IR experiment especially designed to study the growth of an organosilane layer at the interface between a solution and a flat silica surface was presented in an effort to determine the role played by organosilanes at the interface between polymers and flat glass substrates (E2). The study of bulk and interfacial material properties during thin-film deposition of amorphous, hydrogenated silicon nitride was accomplished using in situ ATR IR spectroscopy (E3). A diffuse reflectance FT-IR chamber suitable for in situ and simultaneous analysis of the IR and electronic response of sensors was tested and described in detail (E4). Information on the bonding of organic ligands to hydrous metal oxide surfaces, necessary to gain insight into the mechanisms of surface reactivity, was obtained by using ATR FT-IR spectroscopy (E5). The chemical oxidation of hydrogen-terminated silicon(111) surfaces in water was studied in situ with FT-IR in the multiple total internal reflection mode (E6). In situ ATR FT-IR spectroscopy was applied to the study of carboxylate-bearing, siloxane-anchored, self-assembled monolayers (E7). An FT-IR spectrometer was interfaced with a surface balance and a new external reflection IR sampling accessory, which permitted the acquisition of spectra from protein monolayers in situ at the air/water interface (E8). During the chemical vapor deposition of silicon carbide from methyltrichlorosilane, the gasphase species were analyzed in situ by absorption FT-IR spectroscopy (E9). A sample chamber was designed to simultaneously measure the dc resistivity and IR transmission of C60 thin films in situ while the films are doped with alkali metals (E10). In situ FT-IR reflection/absorption studies of the curing chemistry of polyimide thin films on Cr and Cu surfaces and of the thermal stability of the resulting thin-film interfaces when exposed to air at elevated temperatures were reported (E11). The adsorbed selfassembled submonolayer and monolayer structure, orientation, and chemical interaction at the interface of nonmetallic semiconductors were studied by IR reflection spectroscopy (E12).
ATR FT-IR spectroscopy was used to study amine- and sorbitan ester-based surfactant adsorption in situ at the solid/liquid interface (E13). The growth of thin films of corrosion products on Cu and Ni in flowing humid air was studied in situ by IR reflection absorption spectroscopy (E14). The adsorption of sodium dodecyl sulfate and sodium dodecylbenzenesulfonate, and the coadsorption of those surfactants with a probe species, benzophenone, at the sapphire/water solution interface were examined via polarized ATR FT-IR spectroscopy (E15). The process of vapor deposition polymerization of N-methylolacrylamide was observed in situ using FT-IR reflection absorption spectroscopy (E16). An emission FT-IR technique for epitaxial film thickness monitoring was developed and used for real-time measurement of growth rates and incubation times (E17). In Situ Electrochemical Studies. Polarization modulation FT-IR reflection absorption spectroscopy was used in situ to study the structure of octadecanethiol when adsorbed to gold electrode surfaces (E18). The chemical composition of the surface films formed on lithium in alkyl carbonate solutions was explored using surface-sensitive FT-IR spectroscopy in the external reflection mode (E19). Another study of the surface films formed on lithium was performed using in situ electromodulated IR reflectance or subtractively normalized interfacial FT-IR spectroscopy (E20). In situ FT-IR thin-layer spectroelectrochemistry was employed at a flat mercury-based electrode to obtain, uniquely, the spectrum of the reduced form of flavin adenine dinucleotide in neutral solutions (E21). Cyanate and thiocyanate adsorption processes were studied in situ using vibrational spectroelectrochemistry to study the structure and dynamics of the electrochemical double layer (E22). Step-scan interferometry was applied to the study of carbon monoxide adsorbed on platinum electrodes and to study the Fe(CN)63-/4- redox couple (E23). The electrochemical hydrodimerization of formaldehyde was studied by potential-dependent and time-dependent in situ FT-IR spectroscopy (E24). The adsorption of sulfate on gold(111) in acidic aqueous media was studied by in situ reflection/absorption spectroscopy as well as by scanning tunneling microscopy (E25). The photoelectrochemical characteristics of the p-silicon-potassium ferri-/ferrocyanide electrolyte interface were studied by in situ ATR FT-IR spectroscopy (E26). The nature of the strongly adsorbed species of ethanol on polycrystalline platinum was established using in situ FT-IR spectroscopy (E27). Oxidation of LiAsF6-acetonitrile and LiClO4-acetonitrile solutions containing 0.003-0.05 M H2O were studied on platinum and glassy carbon electrodes by in situ FT-IR (E28). A simple, convenient, and versatile thin-layer reflection FT-IR microspectroelectrochemical cell was described and characterized (E29). IR reflectivity measurements of the equilibrium phases in alkali metal-doped C60 films and single crystals were presented (E30). The investigation of the coadsorption of carbon monoxide with sulfur or bismuth atoms at a platinum electrode using in situ infrared spectroscopy and quantum chemical analysis was described (E31). In situ IR reflection spectroscopy with electrochemical modulation was used to study the structure of the double layer for the polycrystalline gold/dimethylacetamide interface (E32). An electrochemical and spectroelectrochemical study of the adsorption and oxidation of methanol on platinum single-crystal electrodes was carried out in alkaline media (E33). External reflection/ absorption infrared spectroscopy and ATR spectroscopy were used to perform in situ studies of conducting polymer electrodes (E34).
An integrated calcium fluoride crystal IR thin-layer cell was designed and applied to the identification of the electrochemical reduction product of bilirubin (E35). The IR spectra of molecules adsorbed on a silver electrode surface were studied by using the Kretschmann ATR method, where a thin metal film evaporated on an ATR prism was used as the electrode. The sensitivity of this technique was found to be ∼50 times higher than that of reflection/absorption spectroscopy (E36). The first instance of real-time monitoring of electrochemical dynamics by submillisecond time-resolved surface-enhanced ATR infrared spectroscopy was reported (E37). The electrooxidation and electroreduction of propargyl alcohol on platinum electrodes in acid solutions was studied using differential electrochemistry, mass spectrometry, and in situ FT-IR spectroscopy (E38). The redox process of poly(2-naphthol) films was studied using multiple internal reflection FT-IR spectroscopy (E39). Using in situ ATR spectroscopy, the anion content in polyaniline as a function of the pH and the electrode potential was determined (E40). In situ scanning tunneling microscopy and IR spectroscopy were used to study the electrooxidation of phenoxide to oligophenol on gold(111) electrode surfaces (E41). The characterization of the NO adlayers formed at platinum single-crystal electrodes in contact with acidic solutions of nitrite was performed using in situ IR spectroscopy (E42). The adsorption of phenol (E43) and 1,4-dibromobenzene (E44) on gold electrodes was studied using in situ IR spectroscopy and in situ surface-enhanced Raman spectroscopy. Irreversibly adsorbed cyanide adlayers on a platinum(111) electrode in basic sodium perchlorate electrolytes were studied by IR reflection/absorption spectroscopy (E45). The kinetic aspects of the oxidation of 2-propanol on platinum electrodes were investigated by in situ time-resolved IR spectroscopy (E46). The modeling of a spectroelectrochemical cell with radial liquid flow for in situ external reflection IR spectroscopy measurements was presented (E47). Adsorption of ethyl xanthate anions on a silver electrode was studied using in situ IR spectroscopy in a thin-layer flow cell (E48). In situ IR reflectance spectroscopy was used to study the electroadsorption and oxidation of ethanol at polycrystalline iridium and rhodium electrodes (E49). Reduced carbon dioxide on polycrystalline palladium and platinum electrodes in neutral solution was studied using in situ IR spectroscopy (E50). Construction of a reproducible, reliable, and rugged iridium-based microelectrode was described (E51). The utility of IR reflection/absorption spectroscopy for examining structure and bonding for model electrochemical interfaces in ultrahigh vacuum was illustrated, focusing specifically on the solvation of cations and chemisorbed carbon monoxide on platinum(111) (E52). The reaction processes of WF6 with photochemically deposited a-Si:H films were studied in situ using polarization modulation IR spectroscopy and quadrupole mass spectrometry (E53). Surface oxide species produced by the electrochemical pretreatment of a glassy carbon electrode were characterized using in situ IR spectroscopy and electrochemical techniques in aqueous water and deuterated water solutions (E54). In Situ Studies of Catalysis. Information on the bonding of organic ligands to hydrous metal oxide surfaces in order to gain insight into the mechanisms of surface reactivity was studied using in situ ATR IR spectroscopy (E55). In situ IR spectroscopy was employed to study the system of rhodium-exchanged NaX zeolite with different metal dispersion during syngas reactions Analytical Chemistry, Vol. 68, No. 12, June 15, 1996
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(E56). A double-chamber flow cell was developed and applied to the in situ IR study of chemical reactions in Ziegler-Natta catalyst systems (E57). The role of the catalyst support in methane reforming with carbon dioxide over rhodium catalysts was studied using in situ IR spectroscopy (E58). Carbon monoxide adsorption and oxidation over Cu2MnOx catalyst from room temperature to 373 K were studied using in situ IR spectroscopy (E59). Combined in situ IR and on-line mass spectrometric studies provided simultaneous information of the adsorbed species on V2O5-TiO2 catalysts and the composition of the reaction products during the selective catalytic reduction of nitric oxide (E60). The design and application of a new reactor for in situ IR spectroscopic investigations of heterogeneously catalyzed reactions was presented (E61). High-temperature in situ IR spectroscopy was used to investigate the surface species present on copper-ZSM-5 catalysts during the reduction of NOx with propylene in a lean environment (E62). The interaction of NO and CO on Rh-SiO2 and Ce-RhSiO2 catalysts were studied at temperatures up to 723 K using in situ IR spectroscopy (E63). Studies of a phosphine-palladium catalyst for the hydrocarboxylation of olefins were performed in situ using IR spectroscopy (E64). The reaction between [Ru3(CO)9(CCO)]2- supported on magnesium oxide and the alkylating agent CH3I was investigated in an attempt to understand its reactivity and mechanism using in situ IR techniques (E65). The formation of RhI(CO)2 from Rh6(CO)16 impregnated on SiO2 and its reactivity toward C2H4/H2 have been investigated using in situ IR spectroscopy (E66). Site-blocking effects in ethylidene decomposition kinetics on ruthenium(001) was studied using in situ reflection/absorption IR spectroscopy (E67). Selective catalytic reduction of NO by ammonia over vanadia-titania aerogels (E68) and catalysts (E69) was studied using in situ diffuse reflectance IR spectroscopy. An in situ IR cell capable of studying reactions over heterogeneous catalysts in the temperature range 77-773 K has been designed and applied to the study of formic acid adsorption on Cu-SiO2 catalysts (E70). The adsorption of formic acid on a polycrystalline silver catalyst after various degrees of oxidation was investigated using in situ IR spectroscopy (E71). A combined NMR and in situ IR spectroscopy catalytic study of the conversion of allyl alcohol over zeolite catalysts was reported (E72). In situ IR spectroscopy was utilized to identify adsorbed species on zinc copper chromium oxide and potassium carbonate promoted zinc copper chromium oxide catalysts (E73). Diffuse reflectance near-IR measurements on shallow-bed treated H-Y and H-ZSM-5 zeolite revealed the combination of stretching and bending modes of bridging OH groups as well as their combination with vibrational modes of the zeolite framework (E74). Diffuse reflectance in the mid-IR was used in situ in order to identify the active sites in the reaction of carbon monoxide and hydrogen over lanthanide-modified Rhalumina catalysts (E75). Carbon monoxide-hydrogen reactions over rhodium-titania catalysts at high temperature and pressure were studied using in situ IR spectroscopy (E76). IR spectroscopy was used in conjunction with kinetic measurements in order to clarify the mechanism of the methylation of aromatics over zeolitic catalysts (E77). The transformation of cyclohexene on dealuminated HY zeolites by using an IR reactor/cell coupled to a gas chromatograph (E78). Infrared and molecular simulation studies of adsorption of simple gases such as methanol and water on aluminophosphates were reported (E79). An in situ dynamic study of the hydrogena100R
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tion of but-1-yne on platinum-silica catalysts using IR spectroscopy was performed (E80). A metal reactor, designed to approximate a well-stirred tank reactor, was fabricated and applied in the in situ IR spectroscopic studies of heterogeneously catalyzed reactions (E81). A correlation between spectra and catalyst activity was investigated via in situ diffuse reflectance IR spectroscopy of probe molecules adsorbed onto CoMo-alumina hydrotreating catalysts (E82). A detailed investigation of a wellknown photoreaction, phenol photodegradation, in the presence of titania was carried out (E83). Measurements of OH fundamentals and combination bands were performed using in situ diffuse reflectance spectroscopy in order to investigate MFI-type zeolites (E84). The reactivity of adsorbed NO and CO was studied using combined in situ IR spectroscopy and mass spectrometry on rhodium-silica catalysts (E85). General Applications of in Situ IR Monitoring of Chemical Processes. The capability of fiber-optic ATR in the mid-IR using sapphire optical fibers provided a method to probe the chemistry occurring in harsh coal liquefaction streams as well as a diagnostic tool for the thermal testing of jet fuels (E86). Silver halide IR transmitting optical fibers were used in a noncontact mode to deliver and collect IR radiation from a thin liquid sample on a highly reflecting substrate. The system provided a quantitative IR spectrum with minimal sample preparation (E87). A strategy was tested for the monitoring of powder blending wherein samples were taken throughout the blender vessel and scanned by diffuse reflectance near-IR spectroscopy in order to determine homogeneity (E88). Polymeric materials, specifically polyurethanes, were investigated with the use of mid-IR transmitting optical fibers acting as internal reflection elements (E89). Real-time ATR IR spectroscopy was used to follow the conversion during acrylate polymerizations by measuring the presence of functional groups at finite depths from the crystal surface (E90). The mechanism of EPM peroxide vulcanizations in the presence of various bis(allyl) esters of aromatic diacids as coagents was investigated using IR spectroscopy in conjunction with equilibrium swelling techniques and atomic force scanning microscopy (E91). The formation of volatile Fe(CO)5 carbonyl from carbon monoxide and the steel walls of an in situ IR cell was studied as the cause of iron contamination of the samples analyzed in the cell (E92). Porous silicon was studied using in situ IR spectroscopy combined with photoluminescence, electroluminescence, and photomodulated and electromodulated IR absorption, when the porous layer was either chemically etched in HF or anodically oxidized (E93). A device for monitoring the surface temperature of materials processed in solar furnaces, based on an IR spectrometer, was used to measure the spectral reflectance or radiance of the samples (E94). A sensor fabricated using fluoride glass optical fibers was used for the in situ IR spectroscopic cure monitoring of epoxy composites (E95). The use of a mid-IR chalcogenide fiber to monitor the lamination of polymer prepregs in an autoclave was described (E96). A study of real-time in situ monitoring of the chemical states of cross-linked urethane solid rocket propellant during curing and aging using an embedded chalcogenide fiber-optic sensor coupled to an IR spectrometer was presented (E97). The potential of mid-IR spectroscopic methods combined with multivariate techniques to address the protein, polysaccharide, lipid, and microbe content of solid-state fermentations was explored (E98).
Remote qualitative identification of materials by vibrational spectroscopy through optical fibers was discussed (E99). Vibrational spectra and adsorption isotherms of sulfate, acetate, and oxalate on titania were measured in situ using a modified ATR IR method (E100). An ATR IR method was developed in order to quantitatively measure, in situ, the surface-facilitated degradation of tetraphenylboron in fully aquated clay pastes (E101). A range of vibrational spectroscopic techniques were used to monitor the supercritical fluid extraction and impregnation of polymers (E102). IR spectroscopy using reactive internal reflection elements was employed to examine some of the conformational characteristics exhibited in three flotation systems: CaF2-oleate, Al2O3-dodecyl sulfate, and KCl-octylamine (E103). The method of supercritical fluid extraction combined with IR spectroscopy was applied to the analysis of fiber finishes on fiber-textile matrices (E104). The polymerization of biphenyl (E105) and the polymerization of polyphenylene (E106) were studied in situ using external reflection IR spectroscopy. Comparative measurements were made using mid-IR reflection, near-IR reflection, and near-IR FT-Raman spectroscopy as different approaches for coupling a vibrational spectrometer to fiber-optic probes (E107). The detection of several gaseous species of chlorofluorohydrocarbons using fiber-optic evanescent field absorption spectroscopy was presented (E108). In situ IR absorption spectroscopy was used to monitor the condensable gases in a chemical vapor deposition system (E109). The use of tapered fiber for mid-IR evanescent wave spectroscopy for enhancement of sensitivity was presented (E110). In situ IR spectroscopy was tested as a method to monitor the UV curing of potential solventfree film coating polymers (E111). In situ UV, visible, and nearIR spectroscopy was used in order to monitor the conformational changes induced by organic vapors on thin films of camphorsulfonic acid fully doped polyaniline emeraldine salts (E112). A study of the epoxy resin-aromatic amine cure mechanism was performed using in situ near-IR spectroscopy (E113). The thermal degradation of polyacryonitrile was studied by a method of differential scanning calorimetry coupled to IR spectroscopy (E114). ENVIRONMENTAL ANALYSIS The use of IR spectroscopy has expanded greatly in the areas of atmospheric chemistry, remote monitoring, and open-path monitoring. The atmospheric work appears to be driven by concerns about gases with global warming potential, ozone depletion, and the Montreal Protocol on Substances That Deplete the Ozone Layer. The importance of the work in this area was highlighted by the 1995 Nobel Prize in Chemistry being awarded to Rowland, Molina, and Crutzen for their work in understanding the chemistry of ozone control in the stratosphere. Environmental and OSHA regulations are driving the interest in open-path and remote monitoring applications. Atmospheric Chemistry. The photodissociation of CF3C(O)Cl at 193 and 248 nm was examined by time-resolved IR and UV spectroscopy (F1). Heterogeneous reaction of gaseous NO2 and HNO3 with particles of NaCl were followed in real time using diffuse reflectance IR spectroscopy (F2). Atmospheric reactions involving CF3OO and CF3O radicals have been studied using longpath infrared spectroscopy (F3). The Cl atom-initiated oxidation of the chloroalkane CHCl3 yields the products HC(O)Cl, CO, and HCl (F4). Two photolysis pathways for ClOClO and ClOOCl were
determined using IR spectroscopy of cryogenically trapped Cl2O2 (F5). IR spectroscopy was used to study low-temperature polar stratospheric cloud model surfaces (F6) and characterize nitric acid hydrates and the heterogeneous reactions of N2O5 and HBr, which are related to ozone depletion in polar regions (F7). Diffuse reflection IR was used to measure the formation of nitrogen compounds on sodium chloride particles exposed to ambient Arctic air (F8). Collisional deactivation of highly vibrationally excited NO2 was studied using time-resolved Fourier transform infrared emission spectroscopy (F9). The photolysis of CH3SSCH3 and its implication in the chemistry of other atmospheric S compounds has been studied (F10, F11). The atmospheric chemistry of unsaturated carbonyls was studied, and the results indicate that reaction with OH and photolysis are two important atmospheric sinks for unsaturated carbonyl species (F12). The reaction between nitrate radical and 2-butyne has been followed with major products and reaction mechanisms discussed (F13). The formation of sulfate by air oxidation of sulfite, thiosulfate, and tetrathionate ions was studied (F14). Evidence for (H2O)2 in the atmosphere is presented (F15). The use of matrix isolation spectroscopy in the study of atmospheric chemistries is reviewed (F16). A number of experiments have been undertaken to more accurately determine spectral parameters of atmospheric gases. These properties such as assigned line frequency, line intensity, IR absorption cross section, and pressure-broadened line widths are critical in accurately identifying atmospheric species and determining column densities, mixing ratios, and global warming potential. The absorption coefficients are reported for CFCs (F17-F21), CH3Br (F20), SF6 (F21), CxFy species (F22), and ozone in the near-IR (F23). Other spectral parameters have been determined for CH4 (F24, F25), ozone (F25, F26), hydroperoxyl radical (F27), H2O ice, amorphous nitric acid solutions, nitric acid hydrates (F28), H2S (F29), cis,cis-peroxynitrous acid (F30), HNO3, ClONO2 (F31), and nitric acid-ice films (F32). A number of different instrumental techniques and lifting platforms, e.g., balloons, planes, and spacecraft, have been used to monitor atmospheric gases. A review on recent applications of FT-IR techniques for balloon-borne remote sensing is given, including a description of an instrument that uses the sun as the source (F33). Balloon-borne remote sensing of trace molecular species based on the mid-IR limb emission have been conducted (F34, F35). Also described is the Smithsonian far-IR spectrometer that measures thermal emission of gases from balloon and aircraft platforms (F36). A number of satellite-borne instruments are also under development or recently deployed (F37-F50). Tropospheric and stratospheric (F51, F52) temperature and water measurements have been conducted using IR sounders. Laserbased scanning spectrometers are also being employed in the study of atmospheric gases. Examples of near-IR diode lasers (F53-F57) and gas lasers (F58, F59) are reported. The sun (F60-F64), the moon (F64, F65), and stars (F66) have been used as spectrophotometer sources for quantitating atmospheric species. Quantitating atmospheric gases in both the time and space domains is also important in understanding the complex chemistries that occur in the atmosphere. FT-IR solar absorption was used to determine the composition of the 1992 tropical stratosphere (F67). The chemical composition of the lower stratosphere was measured using a balloon-based polarizing interferAnalytical Chemistry, Vol. 68, No. 12, June 15, 1996
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ometer in conjunction with overpasses of the UARS satellite (F68). The feasibility of using the nadir-viewing geometry for temporal and horizontal resolution of trace gases is reported (F69). Diurnal variations of some atmospheric gases showed that the daily variability of CO and O3 is too high to be used as surrogate standards for precision and accuracy of the IR technique whereas N2O may be used (F70). The column amounts of several trace gases during the 1991/1992 winter were measured using groundbased spectrophotometers and correlated to dynamic events in the stratosphere (F71-F74). Solar IR spectra recorded between 1980 and 1992 indicated increases in atmospheric burdens of CHClF2 (F75). Seasonal variations of CO vertical distribution were measured from IR solar spectra (F76). Temporal variation of ethane total column abundance above Mauna Loa, HI is reported (F77). Height distribution of methane in the troposphere and stratosphere were determined using a tunable diode laser heterodyne spectrometer (F78). Stratospheric (F79, F80) and mesospheric (F81) ozone amounts have been measured. The column abundance of N2O above Switzerland has been determined back to 1951 (F82). The long-term trend and variability of vertical column abundance of HCN above Arizona and Switzerland has been monitored (F83). Stratospheric concentrations of HF and HCl (F84, F85), HNO3 and O3 (F86, F87), ClONO2 (F87-F89), OH (F90), O3, nitric acid, CFC-11, and CFC-12 (F91) have been followed using several different techniques. Other studies of atmospheric species include the following: identification of ozone isotopes (F92), identification of the HNO3 3n9-n9 band Q-branch at 830.4 cm-1 (F93), fundamental band emission from the v ) 1 levels of CO isotopes (F94), and spectroscopic evidence against nitric acid trihydrate in polar stratospheric clouds (F95). Remote Monitoring. A number of advances in instrumentation technology and data analysis have been reported for remote monitoring of atmospheric components. Advances in hardware technology are described for a commercial instrument (F96). A new extractive FT-IR spectrophotometer is evaluated for assessing indoor air quality (F97). An aircraft-mounted multispectral IR is discussed and used in conjunction with advanced image processing for wide area surveillance (F98). Atmospheric pollutants can be remotely detected using emission spectra with as little as a 7 °C difference between the gas and a background IR emitter (F99). A mobile FT-IR spectrophotometer for monitoring air pollution has been described (F100, F101). The operational characteristics of a Brewer spectrophotometer and a tunable diode IR laser monitor for trace gas analysis in ambient air have been presented (F102). A FT-near-IR spectrophotometer has been evaluated for use in atmospheric monitoring of volatile organic compounds (F103). Imaging indoor gas concentrations by computed tomography and remote sensing by an FT-IR spectrophotometer has been demonstrated (F104). A commercial instrument based on the principle of gas filter correlation nondispersive IR absorption has been optimized to approach 1 ppb by volume precision in the measurement of CO (F105). The design, fabrication, and performance of a spectrophotometer based on prism-echelle designs with two-dimensional InSb detectors for detection of atmospheric-borne chemicals is discussed (F106, F107). Multispectral interference filter arrays may be applied to the development of compact non-dispersive IR sensors for gas analyzers (F108, F109). The feasibility of a FT102R
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near-IR spectrophotometer for atmospheric monitoring of volatile organic compounds has been demonstrated (F110). New light sources for atmospheric applications are being developed. Light-emitting diodes that emit between 2 and 5 mm can be used to analyze for CO2 and hydrocarbons (F111). NearIR diode lasers have been demonstrated for analysis of CO2 (F112) and ammonia (F113, F114). LIDARS systems are being designed and evaluated for remote detection of atmospheric pollutants that are based on mid-IR lasers (F115, F116), frequency tunable mid-IR lasers (F117), and nearIR lasers (F118). The IR Gas Cloud scanner visualizes the spatial distribution of gases that absorb between 2.5 and 14.0 mm with concentrations in the ppm range (F119). The application of advanced computer algorithms such as classical least squares and artificial neural networks (F120), principal component analysis (F121), probabilistic neural network and CLS (F122), ratioing algorithm (F123), and signal processing algorithms (F124) are all improving the ability of IR spectroscopy to detect gaseous pollutants in the atmosphere. Detection of acetone, methyl ether ketone, and sulfur hexafluoride has been accomplished by direct analysis of the FT interferogram which suppresses the broad-band detector signal so that a background spectrum is not required (F125, F126). The use of an FT-IR remote sensor for measurement of chemical emissions at a RCRA treatment, storage, and disposal facility is discussed (F127). A discussion on the measurement of several gases in the IR region is presented (F128). Methane emissions from a landfill were measured using a near-IR diode laser absorption spectrometer with a detection sensitivity of 65 ppb (F129). A midIR DIAL lidar instrument has been built for monitoring light hydrocarbons for petroleum exploration and pipeline monitoring (F130). The diffusive NH3 emission rate from a manure-spreading site was measured using an FT-IR spectrophotometer for remote sensing (F131). IR-based mobile instruments are being developed for the detection of chemical agents primarily for military use, but these systems have environmental applications also (F132, F133). The detection of non-CO2 greenhouse gases at a variety of sites and sources has been demonstrated using passive radiation and open-path radiation measurements (F134). Technical aspects of the EPA’s FT-IR development projects for toxic gas emissions are discussed (F135). Open-Path Monitoring. Open-path infrared spectrometers have received much attention during the past two years. Fieldproven FT-IR spectrophotometers with up to ppb sensitivity for atmospheric gases have been reviewed (F136). Instrumentation, practice, and application of open-path FT-IR atmospheric monitoring has been discussed (F137). The role of open-path spectroscopy in air-monitoring strategies has been evaluated (F138). The advantages, physical limitations, data analysis limitations, and application of open-path FT-IR atmospheric monitoring has been reviewed (F139). Factors involved in correct placement and use of open-path optical systems have been explored (F140, F141). The simultaneous use of two open-path FT-IR spectrophotometers can improve target compound detection limits, but other complexities are added (F142). On-site heated structures are demonstrated to be viable IR sources for open-path FT-IR detection of fugitive gas emission with signal-to-noise ratios and limits of detection comparable to conventional active IR systems (F143). Stray light can
be deleterious to the accurate determination of absorbance values in open-path measurements (F144). The effects of resolution on the IR spectra collected using an open-path IR spectrophotometer and its influence on quantitative analysis are presented (F145). The advantages of using a low-resolution FT-IR spectrophotometer for open-path atmospheric monitoring are discussed (F146). An IR open-path spectrophotometer was evaluated for issues relevant to industrial hygiene monitoring using an exposure chamber and a calibration cell (F147). Several techniques for generating valid background spectra in open-path FT-IR remote sensing have been discussed (F148, F149). Data reduction and analysis routines for open-path optical systems are being developed (F150, F151). The effects of resolution on the performance of classical least-squares algorithms applied to monitoring volatile organic compounds in open-path IR spectrometry are reported (F152). Digital filtering and pattern recognition methods applied to the FT-IR interferograms have been developed to detect methanol vapor in an open-path FT-IR measurement (F153). A method of generating synthetic IR spectra for testing and verification of chemical detection algorithms is presented (F154). The evaluation of open-path IR data using different quantification methods, libraries, and background spectra obtained under varying environmental conditions is discussed (F155). Quality control and quality assurance issues in open-path FTIR measurements have been discussed (F156-F159). Computed tomography is being coupled with open-path IR systems to map gas distributions (F160), plumes (F161), and chemical concentrations (F162). Open-path optical systems are being used to estimate VOC emission rates from area sources (F163), point sources (F164), pilot-scale site disturbances during remediation activities (F165), and test excavations (F166). Field measurements were performed to evaluate measurement of the concentrations of VOCs within operating process units (F167). Industrial and soil remediation sites were monitored by open-path IR spectrometry to determine the VOC concentrations (F168). Emissions from remedial activities at a Superfund site were followed using open-path IR spectroscopy (F169). Open-path FT-IR spectroscopy is being used to determine NH3 emission rates at a salt cake fine repository Superfund site (F170). Open-path FT-IR sensors are used to monitor air quality at the Camacari Petrochemical Complex in Bahia, Brazil (F171), VOC emissions from a waste water treatment plant at Tinker Air Force Base (F172), and urban (F173) and industrial (F174) sites in Germany. An open-path FT-IR spectrometer was evaluated for precision and accuracy and field tested in western Kentucky (F175). A portable open-path FT-IR system has been used to monitor pollutants in various locations in Taiwan as part of an effort to understand smog formation (F176). An open-path FT-IR method was able to detect HF, CF4, CO, COS, and SiF4 toxic gas emission at an aluminum smelting plant (F177). The use of open-path FT-IR spectroscopy to detect operational departures at a production facility plant was evaluated and then tested at a acrylonitrile-butadiene-styrene copolymer production site (F178). Environmental Monitoring. Sampling techniques for IRbased analysis in environmental laboratories have been reviewed (F179). GC/FT-IR was included in a review of chromatographic analysis of environmental samples (F180). IR sensors for environmental gas monitoring are reviewed (F181). A review of FT-
IR spectroscopy, field applications, and future improvements in monitoring air contaminants was presented (F182). The application of on-line FT-IR analyzers to complex waste streams has been described (F183). Methods for reliable quantitation of quartz and calcite in atmospheric aerosols by diffuse reflectance IR spectroscopy have been outlined (F184, F185). Sedimented atmospheric dust has been characterized using IR spectroscopy (F186). A quantitative method for ammonia bisulfate in fine particulate collected from ambient air onto Teflon filters has been developed (F187, F188). Infrared spectral features of atmospheric aerosol containing polyaromatic hydrocarbons and terpenes have been examined (F189). Low-temperature sulfuric acid aerosols that are representative of global stratospheric sulfate aerosols have been studied using IR spectroscopy (F190). SO2 emission in volcanic gases at Asama, Japan (F191), Mount Etna, Sicily (F192), and Vulcano, Italy (F193) have been measured because SO2 emissions may indicate impending eruption. Aerosols generated during the Mt. Pinatubo eruption are predominantly H2SO4-H2O droplets as determined by solar occultation IR spectra (F194). Soil samples were screened after modifying U.S. EPA Method 418.1 for the determination of total petroleum hydrocarbons using IR field techniques (F195). A fiber-optic IR reflectance probe has been used to detect diesel fuel marine dispersed on sea sand (F196). Soil vapors were sampled to detect subsurface contamination using a field-screening method based on a 10-m IR gas cell (F197). Principal component analysis was applied to IR spectra of Saale River sediments to determine main sediment components (F198). Diffuse reflectance IR spectroscopy and mass spectrometry have been used to detect the antiknock fuel additive (methylcyclopentadienyl)tricarbonylmanganese in soil with no evidence of significant decomposition over 8 months (F199). Near-IR spectroscopy has successfully measured the carbon, nitrogen, and phosphorous composition in seston from oligotrophic lakes (F200). A fiber-optic IR probe has been demonstrated for detection and identification of petroleum (F201). Field measurements of nitrous oxide and methane were made using a tunable diode laser (F202). Nitrous oxide fluxes from soils have also been measured using a long-path IR gas monitor (F203). The use of IR spectroscopy in the identification of poly(chlorobiphenyl) from environmental matrixes is described (F204). Methylmercury was determined by purge-and-trap gas chromatography/IR spectroscopy/atomic absorption spectroscopy in thiosulfate extracts of fish and sediment after NaBH4 derivatization (F205). A field-portable FT-IR instrument using a tapered IR fiber optic is demonstrated for analyzing unknown liquid hazardous waste (F206, F207). A compact infrared multigas sensor based on an array of integrated narrow bandpass filters and a PbSe detector array is demonstrated for simultaneous detection of CO and SO2 (F208). An extractive FT-IR spectroscopic stack-sampling technique is being developed by the U.S. EPA for determination of Title III air toxic emissions (F209). Results from a field test of a FT-IR continuous emission monitor at a TSCA incinerator are reported (F210). Concentrations of 11 different stack gases from wood and oil burning boilers were determined using a commercial FTIR gas analyzer with limits of detection found to range from subppm to a few ppm (F211). Extensive laboratory and field tests Analytical Chemistry, Vol. 68, No. 12, June 15, 1996
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were conducted in order to characterize important parameters for the development of a remote passive FT-IR determination of SO2 in heated smokestack plumes (F212). Chemical solvents vapors in a semiconductor production facility are measured using a long-path-length FT-IR spectrophotometer (F213). FT-IR technology was shown to be appropriate for evaluation of acid and solvent stack emissions in the semiconductor industry (F214). FT-IR spectroscopy has been applied to the continuous emission monitoring of cement kilns (F215). The performance and multicomponent analysis of chlorinated hydrocarbons in water using a mid-IR transparent silver halide fiber optic is presented (F216, F217). Further work in using ATR to measure diffusion of chlorinated hydrocarbons into polymer membranes showed the importance of understanding the diffusion for optimizing fiber-optic sensing systems (F218). Time domain information was used to aid in distinguishing between chemicals that have spectral overlap during analysis of trace organics in using sparging-IR techniques (F219). On-line coupling of HPTLC and FT-IR spectroscopy was used to determine edetic acid (EDTA) in water (F220). Total Dinocap content in water was determine using GC/IR and GC/MS (F221). Total CO2 in the range 3-10 mM has been determined in seawater, estuarine water, and freshwater using IR detection (F222). Infrared remote-sensing applications at waste water treatment plants are discussed (F223). Infrared combined with sparging was developed for monitoring volatile organics in waste water at the ppb to low ppm range (F224). The complexation of toxic metals in seawater and waste water solutions to Chlorella vulgaris algal biomass has been studied (F225). An IR study and freeze/ thaw treatment found a characteristic band at 670 cm-1 that gave strong correlation with sludge dewaterability and settleability (F226). Infrared techniques have been compared to conventional analyzers for the real time measurement of vehicle emissions (F227, F228). A FT-IR spectrophotometer remote sensor system has been developed for detection of tailpipe exhaust gases from moving vehicles in order to identify high-polluting vehicles (F229). An FT-IR spectrophotometer has been used in the real-time continuous monitoring of several exhaust gas components (F230). A diode laser system is suggested for dynamic analysis of exhaust gases during typical driving profiles (F231). Exhaust catalyst performance was monitored using IR spectroscopy to detect seven hydrocarbons (F232). Aircraft exhaust has been measured using tunable infrared diode lasers (F233), FT-IR emission spectroscopy (F234, F235), and FT-IR (F236). The application of FT-IR instrumentation for the measurement of non-methane organic gases in exhaust streams has been discussed (F237). The analysis of natural samples for aromatic compounds using GC/IR is reported (F238). GC/matrix isolation IR spectrometry was evaluated for characterizing nitrocresols and related compounds from air sample extracts (F239). Picogram levels (200800 pg) of dioxins and PCBs in groundwater were detected using a GC/cryogenic trapping FT-IR system (F240, F241). Diisopropylnaphthalenes have been examined using several hyphenated techniques including GC/IR because of their importance as potential environmental and food pollutants due to recycling (F242). Methodologies for analysis of PCBs in environmental matrixes using supercritical fluid extraction and chromatography for their separation with identification by IR spectroscopy are described (F243). 104R
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Standardless quantitative analysis of chemical compounds by IR spectroscopy may be performed from the calculated absorbance intensities of the absorption bands (F244). IR spectroscopy has been utilized to analyze fire gases from burning polyurethane foams (F245). IR spectroscopy is assessed for the measurement of greenhouse gases from terrestrial ecosystems with examples for N2O from fertilized grassland and CH4 from forest soil given (F246). IR spectroscopy was used to study pollutant gas absorption onto activated charcoal (F247). The results from measurement of ferrocyanide and oxy anion contents in simulated waste sludges by FT-IR reflection indicate the viability of this approach to characterize highly radioactive waste sludges (F248). IR spectroscopy and GC/MS revealed damage in hepatic DNA of fish exposed to toxic environmental chemicals (F249). Damage was inferred from spectral changes in NH vibrations of nucleotide bases and CO vibrations of deoxyribose. FOOD AND AGRICULTURE Infrared spectroscopies continue to find valuable applications in the food and agricultural industries. The applications include categorizing foods, determination of oil and fat content in food, process and product control, and fodder analysis for livestock production. Reviews of the use of mid-IR spectroscopy in food analysis (G1) and on-line quality and process control (G2) have been written. A technology review of methods using near-IR analysis in the corn milling and refining industry has been published (G3). Application of near-IR in the diary sector has been reviewed (G4). Infrared spectroscopies were used in authentication and classification of food products and determination of contaminant adulteration. Near-IR spectroscopy with principal component analysis was used to discriminate three different orange juice sources (G5) and investigate the adulteration of 65 authentic concentrated orange juice samples (G6). Discrimination of coffee beans from two different species was demonstrated using mid-IR spectroscopy (G7, G8), and the actual coffee content in some coffee mixtures was determined using near-IR and mid-IR spectroscopies (G9). Discriminant analysis in combination with midIR was used to authenticate fruit purees (G10) and used in conjunction with near-IR to authenticate commercial wheat flour (G11). Discriminant analysis with infrared spectroscopy was successfully applied to the authentication of vegetables oils (G12). Near-IR spectroscopy was applied to the detection of foreign substances in milk (G13). Contaminants in white sugar were identified using IR spectroscopy (G14). Attenuated total reflectance IR spectroscopy was investigated for quantitation of adulterants in olive oil (G15). Fat, protein, and lactose were quantitated in unhomogenizied raw bovine milk using near-IR (G16). Protein content was also determined using near-IR and a correlation developed previously for protein content in oil-in-water emulsions (G17). Meanwhile, homogenization efficiencies (G18, G19) and nonlinearities (G20) in IR milk analyzers were demonstrated to affect fat determination. Components that have interfering spectral regions also were demonstrated to affect milk analysis (G21, G22). An attenuated reflectance infrared spectroscopic technique demonstrated rapid quality control for fat and solids in sweetened condensed milk (G23). Trans fatty acids formed during biohydrogenation were quantified in cow milk fat as the methyl ester derivatives using
IR (G24). Two novel trans fatty acids were identified during the study. Near-IR analysis was used to determine fat, protein, and total solids in cheese without sample treatment (G25). Various sample handling and data treatment methods for determining moisture and fat in cheddar cheese using near-IR were compared (G26). Triglyceride levels in cheeses were investigated using capillary supercritical fluid chromatography/infrared spectroscopy/flame ionization detection (G27). “Flora” cheeses showed exclusively unsaturated triglycerides while saturated triglycerides were predominant in cheddar cheeses. Enzymic hydrolysis of milk was analyzed using diffuse reflectance near-IR (G28). Plated colonies of the microorganism Clostridium were identified using IR (G29). In the same study, Raman spectroscopy was used to determine the fat content of milk powder. Finally, near-IR was calibrated for determination of main constituentssprotein, fat, lactose, and total caseinsin goat’s milk (G30). A method for monitoring and predicting enzymic hydrolysis of κ-casein in milk was developed and tested using diffuse reflectance near-IR (G31). With just a few exceptions, near-IR continues to dominate the analysis of grains. Near-IR transmittance and reflectance were found to be comparable in accuracy and reproducibility for determination of protein, oil, and moisture in several grains and seeds (G32). Three commercial near-IR analyzers were compared for the determination of oil, protein, and glucosinolates in canola seeds and found to perform equally well (G33). High correlation with the total level of fatty acids was also found but was not good enough to enable routine use of the method to quantitate. NearIR reflectance was able to predict the wet-milling starch yield from corn with errors at least as good as the reference method (G34). Near-IR reflectance was also shown to determine the protein and oil content of oat cultivars with results well correlated to the reference techniques (G35). Near-IR transmittance of unground brown rice or milled rice adequately screened for amylose content in a breeding program (G36, G37). Protein measurements in rye were demonstrated using near-IR reflectance (G38). Near-IR reflectance at 1680 and 2230 nm can be used to determine hardness in wheat, which was found to be linearly related to grain moisture for hard but not for soft wheat (G39). The feasibility of using near-IR transmittance to perform single-kernel analysis in wheat was explored and showed a model accuracy of 0.85-0.93 with standard errors of prediction of 0.4-0.9% protein (G40). Positioning of the sample kernel in the instrument is a significant factor contributing to variance. Glucose, maltose, and maltodextrins are satisfactorily analyzed in extracts from a process of wheat transformation into sugar using an ATR accessory with a IR spectrophotometer (G41). Infrared photoacoustic spectroscopy showed good predictive ability for analysis of starch, protein, and lipid in single pea seeds (G42). The choice of validation procedures was shown important in using near-IR to predict moisture, proteins, and oils in soybeans (G43). An IR-based milk analyzer offers a rapid approach for the investigation of grain protein solubility (G44). Water uptake and retention in individual grain kernels were observed and mapped using D2O and IR microspectroscopy (G45). Vegetable oils can be differentiated using discriminant analysis with near-IR reflectance (G46), principal component analysis and near-IR (G47), and principal component analysis and mid-IR with the use of attenuated total reflectance (G48). An infrared method has been developed for determination of cis and trans contents
of fats and oils (G49). In addition to determining the total trans unsaturated fatty acid content in partially hydrogenated vegetable oils, the fatty acid composition can be established using GC/IR (G50). Dual-beam infrared thermal spectrometry used for the determination of trans fatty acid content in margarine showed an improvement in sensitivity of at least 2 orders on magnitude over the traditional IR technique (G51). The total dimer and polymer triglyceride level in used frying fats and oils was quantitated using near-IRS (G52). A quantitative method for peroxide values in vegetable oils has been described using IR (G53). IR spectroscopy was used to monitor the oxidation of edible oils and determining the oxidative state of the oils (G54). The absorption of oleic acid (G55) and soybean oil triglycerides (G56) on silicic acid has been studied using diffuse reflectance IR spectroscopy. Bread making has also been investigated using IR and nearIR spectroscopies. For example, five parameters important to the bread quality of wheat flour were explored using near-IR but only water absorption was successfully modeled (G57). However, nearIRS did successfully model moisture and protein in whole grains of bread wheat (G58). Investigation of the interactions between emulsifiers with gluten and amino acids (G59) revealed that the amino acid GLx in gluten is critical for complexation of gluten. Additional investigation into the interaction of emulsifiers with starch and flour and in dough provided data on the strength of bonding and the nature of the bonding emulsifier and dough component (G60). Attenuated total reflectance IR spectroscopy was demonstrated as a means of assessing quality of processed meat products by determining the protein-to-lipid ratio (G61). Protein and fat content in meat was determined using IR (G62). Fiber-optic nearIR instruments were shown to be suitable for determination of fat and moisture in salmon fillets while near-IR diffuse reflectance was used to determine fat, moisture, and protein contents in whole and ground fillets (G63). Near-IR reflectance and transmittance analyses were performed on sausage and sausage mixes for prediction of NaCl content (G64). The management of livestock fodder has also received attention using IR and near-IR spectroscopy. Near-IR reflectance was applied to prediction of the nutritive value of Mediterranean tree and shrub foliage (G65), total and phytate phosphorus in vegetable feed stocks (G66), chemical composition and energy value of compound feeds for cattle (G67), and analysis of fresh grass silage (G68). Calibration methods for using near-IR reflectance to discriminate fodders to improve accuracy and reduce calibration costs (G69) and for single- and multiproduct calibrations (G70) have been explored. Near-IR and mid-IR diffuse reflectance spectroscopies were compared for the quantitative determination of the composition of forages and byproducts (G71). Nutrient digestion of hay by cattle may be correlated with specific regions of the near-IR spectrum (G72). Plant studies were impacted by IR and near-IR spectroscopy. Quantitative and qualitative analysis of sugar beet leaves by nearIR can be used to study the influence of fertilizers and predict protein, nitrogen, and saccharides (G73). Compositional modification of the plasma membrane from spinach followed by horizontal attenuated total reflectance (HATR) IR could be associated with flower induction (G74). Nonstructural carbohydrate can be determined using near-IR (G75). Near-IR was used to study lipid concentrations in aerial plant tissue of maize (G76). Near-IR shows the potential for performing chemical analysis of Analytical Chemistry, Vol. 68, No. 12, June 15, 1996
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heterogeneous and biologically complex grasslands (G77). Chitinase activity in tall fescue grass seedlings was measured using near-IR (G78). On-line control of the brewing process has received the attention of several investigators. Near-IR transmission spectroscopy was used to determine glucose, maltose, maltotriose, nitrogen, free R-amino nitrogen, and β-glucans in wort as part of an effort in process control of mashing (G79). Even though midIR spectroscopy gave slightly better results in determination of fermentable sugars and nitrogenous compounds in wort, near-IR was recommended for in-line process control of mashing because of simpler sample handling (G80). Sample selection spectrophotometer calibration and standardization were discussed as it relates to multivariate calibration and calibration transfer of near-IR analysis in malting and brewing (G81). Near-IR reflectance spectroscopy was shown to be a rapid method for determination of glycogen (G82) and trehalose (G83) in pitching yeast. Alcohol content and original extract was monitored in the brewing process using near-IR with a single-strand fiber-optic accessory (G84). The use of near-IR in-line and density/sound velocity methodologies were compared for use in blending high-gravity beers (G85). NearIR transmittance for fast process and product control in breweries and malthouses has been reviewed (G86). First-derivative spectra in the mid-IR region can be used to determine ethanol content in beers (G87, G88). A near-IR method has also been developed for ethanol as well as maltose in beers (G89). Total soluble nitrogen and free amino nitrogen in beers can be predicted using dry extract spectroscopy with IR reflection, but bitterness was poorly correlated (G90). A qualitative description of constituents in spirits can be obtained using GC/IR/MS (G91). The effects of H2O, pH, ionic strength, and physical state in sugars and carbohydrates were explored in order to better understand calibration accuracy differences in near-IR seen between high-moisture and dried materials (G92). Spectral features that were characteristic for identification purposes to glucose, fructose, and sucrose in near-IR and mid-IR spectra (G93) were identified. Infrared spectroscopy was used to follow changes in heattreated soybean proteins (G94). Multistage retrogradation of potato starch was observed using IR spectroscopy where the firststage results from crystallizing amylose regions and the secondstage results from amylopectin crystallization (G95). Hydration of the water-insoluble high-Mr glutenin by IR and NMR revealed structural and molecular interaction changes (G96). Starch damage determination by four techniques including near-IR spectroscopy have been compared (G97). Acid-catalyzed hydrolysis of starch can be monitored using near-IR spectroscopy (G98). IR and Raman spectroscopy are capable of evaluating the loss of lignin and hemicellulose following specific pretreatments of plant fibers (G99). Protein conformations were explored using IR for the gobular proteins 11S and 7S from peas (G100) and β-conglycinin in soybeans (G101). The IR technique was more sensitive to some conformational changes than was circular dichroism. Glycosidic linkages and stereochemistry in several oligosaccharides in the crystalline state were studied using IR and Raman spectroscopies (G102). Rapid determination of the double-bond configuration and position in cyclic fatty acid monomers from heated flax seed oil is possible using GC/MS and GC/matrix isolation-IR (G103). The double-bond positional isomerization process in linseed oil 106R
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has been studied using UV, IR, and Raman spectroscopy (G104). IR spectroscopy was demonstrated as a quantitative method for determining food-grade mineral hydrocarbons in diet and tissue (G105). The quantitation of poly(ethylene glycol) in nutritional studies appears to be possible using IR (G106). IR spectroscopy and GC/MS were used to identify and quantify components in a commercial liquid smoke flavoring (G107). Identification of nonvolatile compounds in microwave susceptor packaging designed for browning foods in microwave ovens was accomplished using SFC/IR and SFC/MS (G108). COAL AND CARBON High Carbon Black-Loaded Samples. An easy sampling technique of wet grinding was devised to make KBr disks from insoluble, cross-linked elastomers for transmission IR examinations. The method was used to obtain satisfactory transmission IR spectra of some cured rubbers including samples with a high carbon black load (H1). External reflection FT-IR spectrometry in combination with partial least-squares regression allows qualitative and quantitative analysis of rubber materials with a high carbon black content (up to 35% w/w). The method developed proves to be reproducible and yields reliable qualitative information. The prediction potential of the method is shown to be sufficient for semiquantitative analysis (H2). Three novel methods of obtaining vibrational spectra of four different carbon black-filled polymers were evaluated: transmission IR spectroscopy using a diamond anvil cell, Raman spectroscopy using 780-nm excitation, and inelastic neutron scattering. None of the three methods was totally satisfactory, but for most purposes IR spectroscopy provides the best results in terms of spectrometer accessibility and the availability of suitable reference collections. Raman spectroscopy was successful in obtaining a spectrum only with one of the four polymers. Inelastic neutron scattering was successful in obtaining a spectrum with all four materials, but this success occurred only with respect to the hydrogenic part of the polymer, and for many materials, it is the herteroelements, O, S, and halogens, that determine the important physical properties of the compound (H3). Three IR spectroscopic methodssphotoacoustic, diffuse reflectance, and transmissionswere evaluated for the qualitative analysis of carbon fibers. The transmission spectra using a potassium bromide pellet are subject to interference by water in the KBr pellet. Extensive dehydration of a KBr pellet at elevated temperatures may cause chemical changes. In contrast, photoacoustic and diffuse reflectance methods are free of water interference. Both methods differentiate the near-surface region of a carbon fiber from its bulk, thus providing information about chemical structures in the near-surface. The photoacoustic, diffuse reflectance, and transmission spectra IR spectra of a carbon fiber have similar band frequencies (H4). FT-IR photoacoustic spectroscopy was used to study the distribution of the oxidation products between the surface and the bulk of the precursor carbon fiber during the stabilization process and to evaluate the degree of oxidation in the near-surface of the stabilized fiber. The distribution of the oxidation products is homogeneous during the first 70 min of the stabilization process. In the last 10 min of the process, however, the near-surface of the carbon fiber is completely oxidized, whereas the bulk has a lower degree of oxidation. It was also found that incomplete
oxidation in the near-surface of a precursor carbon fiber may cause inferior mechanical properties of the fiber (H5). The Kubelka-Munk theory was applied to the thicknessdependent diffuse reflectance of black-painted samples in the midIR. The calculated absorption and scattering coefficients are wavenumber-dependent. The reflectance of the nonideal backing also shows spectral features, which were attributed to the reflections from the boundary surface between the scattering medium and the substrate. The spectral dependence of scattering penetration depth is caused by the scattering and absorption processes. At some wavenumbers, the diffuse reflectance is independent of layer thickness, because of particular values of the parameters of the applied theory (H6). Coal Analysis. The results of applying a least-squares procedure with polynomials are given to obtain a mathematical model of the IR spectra of coals, useful for smoothing, band resolution, peak finding, and data compression (H7). Seven West Virginia coals as well as their N-methyl-2-pyrrolidinone soluble extracts and residues were examined by diffuse reflectance FT-IR spectroscopy. The nature of the OH bands in the raw coals is different from those in the extracts where the OH groups exhibit weaker hydrogen bonding. It is also found that the extracts and residues have the same aliphatic-to-aromatic ratio but more OH groups than their parent raw coals. This indicates that the total OH group content is increased in the extracts and residues after extraction (H8). The gradual changes of the main functional groups of coal samples after chemical pretreatment and solubilization were examined by FT-IR and diffuse reflectance IR spectroscopy. Pretreatment included heating at 300 °C (decarboxylation), oxidation with performic acid, esterification of surface carboxyl with triethyl orthoformate followed by LiAlH4 reduction, Omethylation with (CH3O)2SO2, reduction K-THF-propanol, and reductive methylation with K-THF-CH3I (H9). A set of pyridine-soluble coal extracts, previously characterized by FT-IR spectroscopy using the KBr pellet technique, were characterized using FT-IR diffuse reflectance IR spectroscopy. The aromatic-to-aliphatic CH band area ratios were plotted against the aromatic-to-aliphatic ratios of Ch contents determined by 1H NMR, thus allowing the determination of average absorption coefficients. This quantity varied with coal origin but also differed from that obtained using KBr pellets. This latter procedure produced superior correlations and was preferred for accurate quantitative work (H10). Fourier self-deconvolution improves the qualitative and semiquantitative analysis of FT-IR spectra of coals and their N-methyl2-pyrrolidinone extraction products. Several samples of coals (rank ranging from 85.6 to 92.4 wt % C) were studied. Four spectral regions were selected for discussion, and several ratios were calculated. These data led to a comparison of the structural characteristics of the coals and of their extraction products. The results are discussed in relation to the various trends observed in the samples, the possible relations with Gieseler fluidity of coals, and the sizes of molecular orientations in the relevant cokes obtained by pyrolysis at 1000 °C (H11). A curve-fitting technique based on parameters derived from the literature was demonstrated capable of providing useful and reliable data about coal structure and functional group concentrations when applied to selected regions of the FT-IR spectra of coal (H12).
Dry-phase oxidation of two subbituminous coals and a lignite was carried out in a fluidized-bed reactor at 200 °C, at different oxygen partial pressures and reaction times up to 4 h. The formation and evolution of various oxygenated functional groups (ester, carboxyl, ketone, hydroxyl) was investigated by FT-IR spectroscopy using a curve-resolving procedure and acetylation of coal samples. The development of alkali solvolysis of the coal as a function of reaction time was studied and the average molecular weight of regenerated humic acids (RHA) extracted from the oxidized coal was determined. The lower molecular weight of RHA extracted from highly oxidized coal samples suggests that besides the buildup of various oxygenated functional groups, the development of alkali solvolysis also results from concomitant “depolymerization” of the coal cross-links and formation of ester groups hydrolyzable in basic solution. The FT-IR results were correlated with the development of alkali solvolysis. Some oxidation pathways are proposed (H13). A modified Leitz hot stage fitted to a Spectra-Tech microscope and interfaced with a Nicolet 20-SXC FT-IR spectrometer was used to collect IR spectra from a series of heat-treated coal or kerogen samples. Spectra were collected in the reflected light mode prior to and then during or after heat treatment. This provided a means to monitor organic functional group changes or depletion resulting from heat treatment. The IR spectra obtained were similar to diffuse reflectance IR spectra. A significant portion of the surface coke generated during pyrolysis of oil shales may originate from migration of hydrocarbons to the particle surface, where they disproportionate to volatile matter and semicoke rather than strictly from surface coking of vapor-phase hydrocarbons (H14). The applicability of the reflectance micro-FT-IR technique to analyze the distribution of functional groups in coal is discussed. The spectra of a series of coals from lignite to anthracite obtained using reflectance micro-FT-IR were compared with those of the same materials but obtained using transmission micro-FT-IR and KBr pellet techniques. This comparison shows that (1) band absorbances in the transmission mode are much higher than those in the reflectance mode, (2) band peak positions are the same in the transmission and reflectance modes as long as KramersKroning transformation is applied, and (3) the 700-900-cm-1 aromatic-dominated region has higher absorbance in the reflectance than the transmission mode. The results indicate that reflectance spectra can be utilized to characterize functional groups in organic matter under most conditions. The ease of sample preparation, the potential to analyze large intact samples, and the ability to characterize areas as small as 30 µm are the main advantages of reflectance micro-FT-IR (H15). Infrared microspectroscopy was employed for the in situ examination of coal macerals during oxidation. From a comparison of reconstituted spectral data based on the individual maceral characteristics with those extracted from powdered bulk sample, the reactivity of powdered coals cannot account either for the mechanisms occurring at the maceral level or for possible maceral/maceral or mineral/maceral interactions during oxidation. In addition, the coupling of IR spectrometry to a microscope provides more accurate quantitative data on the intensity of IR bands, which are usually perturbed either by diffusion or water adsorption on KBr pellets. The data presented confirm that coal is a highly heterogeneous material not only from a sedimentology or composition standpoint but also from the reactivity standpoint (H16). Analytical Chemistry, Vol. 68, No. 12, June 15, 1996
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A modified method is described for the determination of the aromatic, naphthenic, and paraffinic carbon contents of blended base oils by IR spectroscopy. These oils are blends of mineral base oils and linear alkylbenzenes (LAB) or heavy alkylated benzenes (HAB). The Brandes equation has been modified to account for the absorptivity of LAB/HAB, using 13C NMR data as a reference. The results obtained by applying the new equation to such blends agree well with those obtained by NMR. This new method can be used for rapid and convenient quality control during base oil production (H17). Diamond-Like Carbon Films. The influence of hydrogen incorporation on the microstructure of hydrogenated amorphous carbon (R-C:H) films has been studied in detail by applying several complementary methods, i.e., elastic recoil detection analysis (ERDA), hydrogen evolution, and IR absorption measurements, to two series of samples prepared by two different techniques, representative of diamond-like and polymer-like R-C:H. The analysis of the changes of the IR vibrational spectra over a large frequency range upon annealing at increasing temperatures up to 600 °C allowed one to obtain insights into both the C-H and C-C bonding modifications (H18). Data on the optical response of amorphous carbon layers are presented. The layers investigated range from well-insulating polymer-like layers via hard “diamond-like” layers to well-conducting graphite-like layers. The spectral range investigated covers parts of the far-IR, the mid-IR, the near-IR, and the visible spectral regions. The data are presented and discussed in terms of parameters of commonly accepted dispersion models and absorption assumptions (Penn model, Lorentzian oscillator model, Urbach edge, Tauc edge). Special attention is paid to the refractive index dispersion behavior. The influence of contaminations such as nitrogen and oxygen is investigated (H19). Polycrystalline and homoepitaxial diamond films deposited from 12C- and 13C-containing gases were characterized by FT-IR spectroscopy. Some spectral structures in the known C-H stretch band at ∼2850 cm-1 omnipresent in polycrystalline films are related to the incorporation of N. In homoepitaxial diamond films, the isotopic replacement of C, H, and N by 13C, 2H, and 15N reveals that a CH center without N participation is responsible for a new vibrational absorption band observed at 3123 cm-1 in the spectral vicinity of the previously observed 3107-cm-1 absorption band in natural diamond. The bond-centered position can be excluded for this vibrational transition. New H-related electronic transitions were observed in the near-IR at ∼7300 cm-1 (H20). A computer-controlled rotating polarizer ellipsometer, operating in the IR spectral region between 3.00 and 3.75 µm, has been developed for the in situ characterization of amorphous hydrocarbon (R-C:H) thin films, deposited from methane in a rf plasmaenhanced chemical vapor deposition reactor. Spectroscopic IR ellipsometry permits insight into the chemical-bonding structure of R-C:H coatings by the nondestructive detection of IR-stimulated C-H stretch vibrations. It is shown that the sp2 CHx-to-sp3 CHx ratio, the content of bonded hydrogen, the IR line width, and the real refractive index of the films depend on the negative self-bias voltage, which is formed at the samples during the deposition process. A transition from R-C:H films with polymer-like properties to hard R-C:H films was attained at a self-bias voltage of ∼-75 V (H21). Diamond-like carbon (DLC) films, prepared by the dual-ion beam sputtering method on a glass substrate, were thermally 108R
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annealed in vacuum for 30 min at 300, 400, 500, and 600 °C, respectively. Electrical resistivity, IR transmittance, and Raman spectroscopy were used to characterize the films before and after annealing. The results showed that the vacuum thermal annealing caused a decrease and even the removal of bond-angle disorder and an increase of the sp2 C-C-bond-dominated crystallite size and/or number in the films. This then led to decreases in both film resistivity and optical transmittance of the specimens. The most substantial changes in the structure and in electrical and optical properties occurred at a temperature higher that 400 °C. The annealing effects of diamond-like carbon films in vacuum are nearly the same as those in hydrogen or in nitrogen atmospheres (H22). A new deposition method with laser-induced controlled vacuum arc (Laser-Arc) was used for the thin-film deposition of DLC films onto different material (ZnSe, KRS-5, Corning 7059, KBr, KCl, NaCl). Carbon films between 50 and 200 nm thick deposited at different deposition rates (0.1-2 nm/s) and pulse durations (37 µs, 200 µs) were studied. The coated substrates were characterized by UV/visible, near-IR, and Fourier transform IR spectroscopy in the wavenumber range between 400 and 50 000 cm-1 (H23). Raman spectroscopy, FT-IR, and scanning tunneling microscopy (STM) were used to study diamond-like nanocomposite (DLN) and metal-containing DLN (M-DLN) films. The FT-IR spectra showed no appreciable absorption from the C-H stretch vibration band in DLN when 1-kV rf bias voltage was applied. Thermal annealing (450 °C for 2 h) of (a) DLN and Cr-DLN films caused no change in the Raman spectra while (b) for Pt-DLN films there was a blue shift of both the crystalline (G) and microcrystalline (D) graphite-like features, increase in the ID/IG intensity ratio, and a decrease in the line widths. The changes observed were more pronounced in the film with the highest Pt concentration. The STM image of this Pt-DLN film revealed a structure of aromatic graphite rings (H24). Diamond-like carbon film, prepared by the dual-ion beam sputtering method, was irradiated by 110-keV Fe+ ions up to a fluence of 1 × 1017 ions/cm2. The IR absorption spectrum, the electrical resistivity of the film, Raman spectrum, Auger electronic spectroscopy, and reflection electron energy loss spectroscopy were used to characterize the film before and/or after the irradiation. The 110-keV Fe+ ion irradiation led to the breaking of C-H bonds and, consequently, the decrease of sp3 C-H and sp2 C-H bonds. The irradiation also led to the decrease of the bond-angle disorder and the growth in size and/or number of sp2 bond-dominated crystallites in the film. More serious damage was introduced in the near-surface region of the film, and thus more graphite-like structure was formed in this region (H25). Analysis of C60/C70 Fullerenes. The IR spectrum of solid C60 exhibits many weak vibrational modes. Symmetry breaking due to 13C isotopes provides a possible route for optically activating IR-silent vibrational modes. Experimental spectra and a semiempirical theory on natural abundance and 13C-enriched single crystals of C60 are presented. By comparing the experimental results with the theoretical results, the authors exclude this isotopic activation mechanism from the explanation for weakly active fundamentals in the spectra (H26). The harmonic vibrational frequencies of C60 have been calculated at the local distance level by using analytic second derivatives. The calculated values for the observed IR and Raman transitions are in good agreement with the experimental values
and suggest that there are a number of misassigned bands based on thick-film IR and Raman measurements. The calculated transitions have been used to provide tentative assignments to the peaks observed by inelastic neutron scattering and highresolution electron energy loss spectroscopy (H27). The symmetry coordinate treatment of the intramolecular vibration of C60 is developed. The symmetry coordinate is useful to calculate the weighted phonon spectrum and the IR spectrum of isotopically mixed 13Cn12C60-n. The calculated oscillator strength of the intramolecular vibration is not consistent with the IR spectrum observed by Zakhidov et al. The partial substitution causes no drastic change except broadening of the main bands and appearance of weak bands. The calculated weighted phonon spectra are similar to those reported by Deaven and Rikhsar. The effect of symmetry breaking due to the partial substitution of 13C on the intramolecular vibrations as well as on the isotope shift of the superconducting transition temperature (Tc) of the C60 superconductor is discussed (H28). A survey of solvents with a wide variation of solvolysis for C60 and a broad variation in dielectric constant was made for possible red shifting of the linear absorbance spectra. Initial analysis shows that very small shifts are achieved. Molar extinction spectra were measured for C60 in each solvent in both the standard mode and with an integrating sphere. Comparison of the two methods has shown strong scattering effects (H29). High-resolution Raman spectra excited from 1.45 to 1.75 eV are presented for solid C60 films and crystals prepared by four methods. Intersample comparison shows that imperfections introduced in sample preparation can lower symmetries sufficiently to activate silent modes, while oxygen has no visible effect. Unusual resonance and broadening effects observed near 1.6 eV indicate the existence of a weak electronic transition. Explicit calculations for C60 molecules having one or two 13C atoms reproduce the observed spectra and show that isotopic symmetry lowering is manifested in lifting the Hg degeneracies and activation of silent modes through mixing with nearby Raman-active modes (H30). The far-IR transmission of polycrystalline C60 and C70 compacts has been measured from 3 to 330 cm-1 as a function of temperature. Both intrinsic and impurity-induced absorption bands are identified in these samples. The low-temperature phase of C60 is observed to have two IR-active transitional modes at 40.9 and 54.7 cm-1. Samples of C60 exposed to air before cooling to low temperatures contain several additional bands which have been identified with absorbed H2O vapor. A large isotope shift is observed for some of the bands when H2O is replaced with D2O, consistent with rotational or vibrational behavior. For C70, one strong intrinsic band is centered at 21 cm-1 and four much weaker bands occur at 28, 32, 52, and 64 cm-1 (H31). The authors report the measurement of IR transmission of large C60 single crystals. The spectra exhibit a very rich structure with over 180 vibrational absorptions visible in the 100-4000 cm-1 range. Many silent modes were observed to have become weakly IR active. The authors also observed a large number of higherorder combination modes. The temperature (77-300 K) and pressure (0-25 kbar) dependencies of these modes were measured and are presented. Careful analysis of the IR spectra, in conjunction with existing Raman-scattering data showing secondorder modes and existing neutron-scattering data, allowed the selection of the 46 vibrational modes of C60. The authors were
able to fit all of the first- and second-order data seen in the present IR spectra and the previously published Raman data (∼300 lines total), by using these 46 modes and their group theory-allowed second-order combinations (H32). The gas-phase IR emission spectra of C60 and C70 were recorded by FT-IR spectroscopy. The measurements were carried out in the temperature range 500-950 °C, and the band positions were extrapolated to 0 K. In addition to the strong fundamental bands, numerous weak features were observed. The authors attribute these weak bands primarily to binary combination modes (H33). The molecular nature of solid C60 permits observation of very sharp higher-order Raman and IR spectra quite different from the broad features generally observed in solid-state crystals. Observation of these higher-order spectral features together with symmetry-lowering 13C isotope substitutions permits experimental identification of all 46 intramolecular vibrational modes. Knowledge of these mode frequencies and their symmetries provides important information for the interpretation of many experiments including those related to the superconduction of alkali metaldoped C60 compounds (H34). A study of the Raman and IR spectra of the sp2-bonded carbon clusters C60 and C70, performed in the framework of a threeparameter bond-charge model based on a transferable interaction potential, is presented. A consistent calculation of the relative amplitudes and of the static polarizability has been performed with only one additional parameter besides those entering the dynamics. The calculated spectra are compared with the existing experimental data for C60 and C70. Very good agreement is found for the Raman spectrum of both clusters, whereas the agreement for IR spectra is less satisfactory (H35). The authors report results of IR reflectivity and transmission measurements in the spectral range from 50 to 5000 cm-1 for crystallographic {111} and {100} planes of C60 single crystals between 80 and 460 K. The spectra turned out to be highly anisotropic due to differences in geometric resonances. The geometries used allowed detailed simultaneous study of the four IR active F1u fundamental modes together with some weak silent modes and the whole set of second- and third-order combination modes from an analysis of the reflection/transmission response (H36). Absorption spectra are detected for C60- and C602- produced electrolytically in solution at room temperature. Theoretical analysis of the spectrum of C60- by CNDO/S calculations gives an interpretation of the characteristic near-IR bands, the weak visible bands, and the strong bands in the UV region. The emission spectrum of C60- is a mirror image of near-IR absorption band. The nature of the spectrum of C602- is characterized by an orbital picture similar to that of C60- (H37). The authors consider IR absorption in charged and photoexcited C60 using a Su-Schrieffer-Heeger model supplemented by a force field model to treat molecular vibrations. Intensities are calculated by assuming the principal cause of the absorption is the charged phonon effect. The authors’ calculated frequencies for C60 and C60-6 are in good agreement with the experimental results but the calculated intensities are at best in qualitative agreement. For photoexcited C60 and C60-, the calculations indicate a number of additional IR peaks which are in principle accessible to experiment (H38). Analytical Chemistry, Vol. 68, No. 12, June 15, 1996
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The IR spectra of CO2 and N2O absorbed on C60, graphite, and diamond films were recorded at low temperatures. The IR spectra of absorbed CO2 and N2O indicate that only one absorption site is present for all three allotropes. When CO2 is absorbed on C60 and graphite, removal of degeneracy of the ν2 vibrational mode occurs. When N2O is absorbed on the three absorbents, there is no removal of degeneracy of the ν2 vibrational mode, which appears as a single band. Large spectral shifts of the ν3 band and longer desorption times are recorded for both CO2 and N2O adsorbed on C60, relative to the small spectral shifts and shorter desorption times recorded on graphite and diamond. These results indicate a strong interaction of these adsorbates with C60 compared to the other carbon allotropes (H39). A large amount of CO2 absorption in C60 solid was found under a supercritical CO2 treatment. Absorption kinetics show that the process is significantly slower than normal physical adsorptions and is accelerated with increasing temperature. The CO2 IR absorptions are observed at 2329 and 651 cm-1, suggesting a strong interaction between CO2 and C60. Differential scanning calorimetry (DSC) thermograms show a remarkable effect of the CO2 absorption on the orientational phase transition at 250 K of C60 crystals (H40). Thin films of C60 were deposited at 78 K on KBr(100) substrates prepared by cleaving in ultrahigh vacuum. The thickness of the film was monitored by recording the IR spectrum of C60 at different polarizations. FT-IR spectra of CO and CO2 adsorbed on the C60 film were measured under ultrahigh vacuum conditions. At pressures of
