Anal. Chem. 1982, 5 4 , 155R-170R (417) Kawamura, T.; Fukrrmachi, T, Acta Crystallogr., Sect. A (Denmark) 1979, A 3 5 , 831-835. (418) Pietsch, U. Exp. Tel:h, Phys, (Germany) 1980, 28, 75-78. (419) Uno, R.: Ishigaki. &I.“Accuracy in Powder Dlffraction”; op. cit.: pp 07-00. -. (420) Zickert, K.: Vandrey, J.-P.; Steil, H.; Herms, G. Exp. Tech. Phys. (Germany) 1980, 28, 63-68. DATA ACQUISITION, DATA COLLECTION
(421) Fischer, G. R.; Karie, W. T. Acta Crystallogr., Sect. A (Denmark) 1981, A37 (supp.), C-278 (Abstract 12.1-02). (422) Nazarov, Yu. N.; Fedorenko, Yu. G. Prib. Tekh. Eksp. (USSR) 1978, 27, 185; Transi. Instrum Exp. Tech (USA) 1978, 21, 1662-1663. (423) Coyie, R. A. “XIIth international Congress on Crystallography” (2-279 Acta Crystallogr., Sect. A (Denmark) 1981, A37 (supp.) (Abstract 12.104). (424) Hanson, J. C.; Watenpaugh, K. D.; Sieker, L.; Jensen, L. H. Acta Crystallogr., Sect. A (Denmark) 1979, A35, 816-621.
(425) Jenkins, R.; Banks, E. Acta Crystallaor., Sect. A (Denmark) 1981, A 3 7 (supp.), C-283 (Abstract 12.5-04). DATA ACOUISITION. POWDER DIFFRACTION DATA (426) Flala, J. Cesk Cas, Fvz. Sekee A (Czechoslovakia) 1979, 29, 178-179. (427) Morris, M. C.; MaMurdie, H. F.; Evans, E. H.; Paretzkin, 8.; deGroot, J. H.; Hubbard, C. R.; Carmel, S. J. Report NBS-MN-25-16; Nat. Bur. Standards: Washlngton, IX, 1979: 185 pp. (428) Morris, M. C.; MoMurdie, H. F.;Evans, E. H.; Paretzkin, B.; Hubbard, C. R.; Carmel. S. J. Report NBS-MN-25-17; Nat. Bur. Standards: Washington, DC, 1980; 110 pp. (429) “Powder Diffraction File”; JCPDS-International Centre for Diffraction Data: Swarthmore, PA. (430) Brindiey, G. W.; Brown, G. “Crystal Structures of Clay Minerals and Their X-ray Identification”; Mineralogical Society: London, 1980: pp 495. (431) Mendelssohn, M. J.; Milledge, H. J.; Walley, D. Acta Crystallogr.,Sect. A (Denmark) 1981, A37 (supp.), C-278-279 (Abstract 12.1-03). (432) Hubbard, C. R. ”Accuracy in Powder Diffraction”: op. cr.; pp 489-502.
Raman Spiectrometry Derek J. Gardlner Newcastle upon Tyne Polytechnic, Newcastle upon Tyne NE1 8ST, England
The period of this review is from late 1979 to late 1981. During that time around 3700 papers have appeared in the scientific literature dealing with many aspects of Raman spectrometry and extending its use to many new areas of investigation. This large number of publications is due in part to the appearance of 1;he proceedings of the 6th International Conference on Raman Sepctroscopyheld in Ban alore, India, 1978 ( I ) . Once again it has been necessary to e! highly selective in collecting material which has clear relevance to analytical chemistry for the review. Thus, for example, although there are a large number of publications dealing with biological molecules, many of which involve the use of resonance Raman effect, only a few are mentioned here as being of analytical interest. Where ossible, however, reviews in specific areas have been inclu ed to which the reader is referred for a more complete background. A statistical analysis of the development and applications of Raman spectroscopy from 1928 to 1978 has been published ( 2 ) and includes a useful glossary of the different types of Raman excitation. Also some general (3)and industrial (4) analytical applications have been briefly reviewed and the possibilities of using the Raman effect to probe the composition of planetary atmospheres has been discussed (5). The relatively new technique of Raman optical activity has been shown to provide both magnetic and stereochemical information and is expected to attract further interest (6). Raman intensities are fundaimental to quantitative analytical work and relative Raman intensities from molecular orbital calculations can be determined using CNDO/2, INDO, and EHMO methods (7, 8). As in the previous review in this series (9) a separate section dealing with solids hals not been included as many studies in this area are more properly considered as solid-state physics. However, the development of the laser Raman microprobe or MOLE, which has been applied principally to the analysis and characterization of particulate solids, now warrants a separate section. Nevertheless, solids cannot be dismissed without mentioning some of the more clearly analytical work that has been carried out. Teinsile stress has been shown to produce changea in the stretched Si-0 defect sites as well as in the main network structure of optical fibers (10) and at pressures up to 100 kbar the v(0-H) frequency of solid ethanol is markedly reduced due to strengthening of the H bonds (11). The use of Raman spectroscopy to identify cement phases has been reviewed (12)and the technique has been shown to be valuable for diagnosing white (but not gray) portland cement hydration (13). Water in bernalite has also been estimated (14). The AUOH):, minerals, gibbsite and bayerite, have been shown to be distinguishable through their spectra (15) and
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Raman spectroscopy is able to detect K2S04in excess KzSz07 where IR and X-ray methods fail (16). The technique has further been used in a comparativestudy of fossil and modern teeth constituents (17). Other examples of applications to solids include, the determination of lattice temperatures generated by laser heating of silicon crystals by analysis of the ratio of Stokes to anti-Stokes phonon scattering ( l a ) ,a ytudy of Mo and Co oxide catalysts supported on Si02 (19) and A1203(ZO), and an analysis of the species present in amorphous As-Si mixtures (21).
INSTRUMENTATION AND SAMPLING The techniques involved in Raman spectroscopy are continually being developed to improve sensitivity, to handle microsamples and thin films, and to extend application to ever more demanding sample systems. Raman difference spectroscopy now enables very precise measurement of frequency shifts in isotopic dilution studies (22,23)and a two-channel photon counting method for difference spectroscopy has been evaluated (24). A tunable (355-755 nm) pulsed Raman spectrometer has been developed having a pulse duration of 3.2 ns with a peak power of >lo0 kW which allows processes occurring in the picosecond time scale to be probed (25). The first experimental results of transient coherent Raman scattering from liquid MeCC1, have been reported (26). A system has also been developed for observing angular resolved Raman iacattering which uses fiber optic probes; it is hoped to prove to be a valuable technique for examining surface enhancement (effects (27). Methods of improving sensitivity are always $welcomeand the use of exit slit plane multiplex detection has been shown to give a X103 improvement (28). A useful talbulation of Kr+ laser plasma lines has also been produced (29). Microprocessor control and handling of spectral data proceeds apace (30),digital methods for curve smoothing and differentiation have been improved (31),and a computer-aided Bystem for interpreting infrared and Raman spectra, based on the GRISE program, has been statistically evaluated (32). Sample presentation is often critical in Raman spectroscopy and reports of new cells are worth noting. Detection of low concentrationsin microvolumes using both microcells (33)and a backscattering spinning cell (34) have been described. A new technique for dealing with highly absorbing liquids referred to as, “jet flow Raman spectroscopy”, has been used to observe the resonance Raman effect in aqueous CuC12 solutions (35). Multipass systems for gases (36) and easier to use cells for studying electrode and flow systems (37) have been described. Problems caused by local overheating when studying colored samples have often been overcome by spinning methods. However, a technique which involves placing
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a cylindrical lens before the sample, which creates a line focus thus reducing the laser power density, has been shown to be equally effective (38).A related approach has used fiber optics to spread the illumination over the sample surface (39). New cells have also been designed to cope with variable temperatures and high pressures (40,41) and some of the problems associated with using diamond anvil cells have been resolved (42).
Studies of thin films are inherently difficult with the Raman technique; however, conditions can be improved by utilizing surface electromagneticmodes and integrated optics (43,44). A total internal reflection method also has been examined and, using sapphire as the internal reflection element, spectra from polystyrene fiis of thickness 0.006-0.2 wm were obtained (45). Finally, remote Raman studies have been reviewed (46) and a LIDAR study of H 2 0 in the atmosphere has been made up to 1km with 30 m resolution using a frequency-quadrupled YAG laser source (47). The Raman and resonance Raman effects have also been used as detection systems in liquid chromatography (48-50).
LIQUIDS AND SOLUTIONS The liquid or solution phase is probably the most commonly studied phase in Raman spectroscopy. This section is restricted mainly to examples of solute characterization and detection in solutions, studies of liquids and solutions under nonstandard conditions, and studies of liquid crystals. The advantagesand disadvantages of using the technique,for water pollution studies have been discussed (51). A stopped-flow method has been used to observe the spectrum of the phenoxy radical produced by oxidation of phenol with Ce(1V) (52)and a temperature-jump study of nucleoside base solutions has been carried out (53). In some solutions solvent-solute interactions are extremely weak resulting in very small perturbation of the spectra. However, by using Raman difference spectroscopy small frequency shifts can be reliably detected. For example, shiftx as small as 0.06 cm-l have been detected in benzene-CSz, benzene-pyridine, and MezCO-CHCl, solutions (54). Electrolyte solutions and the nature of ion-solvent interactions continue to be of wide interest (55). A study of the effect of Na+ ion concentrationon aqueous solutions of a range of oxyanions suprisingly suggests peak area ratios are not necessarily the best measure of concentration (56). Detection M for SzOt- and 3 X M for SO2 limits between 8 X have been established for a range of sulfur oxyanions in aqueous solution (57) and a study of basic aluminosilicate solutions has been reported (58). Raman spectroscopy has further been used to determine stability constants in aqueous MgN02 and CaN02 (59). Nonaqueous solutions also have been investigated, and typical are studies of electrolyte interactions in formamide (60) and liquid NH3 (61). The mechanism of COz (62) and H20 (63) solubility in silicate melts also has received some attention. Several Raman studies on liquids and solutions at high pressures have been reported. The method has distinct advantages over infrared as the necessarily long path length hydrostatic cells can be used and the full vibrational spectral range can be examined using sapphire or diamond windows. Pressure effects on the polarized spectra of aqueous [Hg(CN),I2- from 0 to 8.5 kbar have suggested a mechanism for v(CN) splitting in the solid state (64). The n-alkanes, 2methylbutane, and 2,3-dimethylbutane have been shown to increase the ratio of gauche to trans linkages as a function of pressure (65, 66) and in a study of bromoalkanes, pressure-induced conformational volume changes have been determined (67). Reorientational correlation functions can be obtained from an analysis of Raman bandshapes and these have been investigated as a function of messure for the C6H6-CHC13systek (68). Studies of liauid crvstals have been reviewed (691. The accordian mode bf the h t y l chain of EBBA has been &signed and shown to be conformationally sensitive (70). Spectra of thin films of the nematic liquid crystals MBBA and NP-BA have been obtained from samples sandwiched between pretreated glass and quartz plates, and intensity ratios were shown to correlate with molecular orientation (71). A novel approach in this work has involved the use of resonance Raman scattering from @-caroteneembedded in liquid crystals ( 72). 166 R
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GASES AND MATRIX ISOLATION Pure rotation and vibration-rotation studies continue and have been shown to yield high precision molecular parameters (73). A useful review of the vibrational characteristics of nitrogen oxides has been published (74) and the feasibility of using the Raman technique to determine natural gas components has been demonstrated (75). Analysis of the gas headspace in harmacutical ampules is another novel application (76). zoncentration profiles in jet flows (77, 78) and a rapid method for determining gas temperatures from rotation spectra have been reported (79). Several studies of flames have appeared and a review of combustion diagnostics describes the methods involved (80). Temperatures in flames can be determined from the Nz spectrum (81)which appears to be superior in this respect to COz (82). The need to exercise care when measuring temperatures in flames producing fluorescin species has been emphasised by a study of NH3-02 flames f83). Temperature profiles of HBr inhibited flames also have been determined (84). In a study of a laminar flame-wall interface it was found unexpectedly that although there is a large temperature difference near to the wall and in the free flame, the concentration profiles of CHI, CO, and COz are similar in both locations (85). Work on molecular ions in noble gas matrixes has been reviewed (86). A novel analytical application of matrix isolation Raman spectroscopy involves spraying cuts from the effluent stream of an Ar gas chromatography column onto a cold finger. The cold finger rotates to freeze sequential cuts into 1mm diameter spots which are analyzed spectroscopically. In this way trace amounts of organic substances in water have been detected (87). Several polynuclear species have been characterizedBiz, Bi3,and Bi4 (88-90), Pb2,Pb3, and Pb4 (911,and Sn (92). The products of the O3 + C1 reaction have been trappei and identified (93) and the isotopic fine structure of A12C16has been examined (94). Matrix isolation spectra of group 2B fluorides and mixed halides have been observed (95) along with spectra of POC13 (96) and (SO), (97).
BIOLOGICAL MOLECULES AND POLYMERS The application of Raman spectroscopy to the study of biological species is growing rapidly. As a result only a few representative examples will be mentioned here along with those having a novel aspect. There are several reviews which adequately cover the material omitted. Both spontaneous (98, 99) and resonance Raman (100) applications have been reviewed along with studies of metalloproteins (101) and the uses of Raman difference spectroscopy (102). Protein structure and conformation has received considerable attention (103). Changes in the amide I11 region on addition of Ca2+ions have been interpreted in terms of increased a-helical content in troponin C (104) and it seems that eye lens protein studies may provide useful information on cataract formation (105). The possibilities of studying plant, bacterial, and mammalian cells continue to be explored (106); for example, accumulation sites and hydrocarbon composition in Botryococcus braunii have been determined (107) and ordering of cellulose chains within fiber cell walls has been indicated (108). The structure and composition of cell membranes can also be probed (109,110). Raman techniques have been used to construct phase diagrams for binary phospholipid systems using deuterated componentsas conformation indicators (111) and the effect of temperature on lysozyme-phospholipid interactions has been studied (112). The C-D stretching region of perdeuterated 1-monostearin can be interpreted in terms of a lamellar structure being preferred by lecithin-bile salt mixed micelles (113). Assignments for the a-Me and ester-Me vibrations in poly(methy1 methacrylate) have been established using deuterated derivatives (114). The effects of stretching polymer materials can be readily investigated. Quantitative information about molecular orientation in uniaxially stretched polystyrene films (115)and phase orientation in polyethylene have been deduced (116) from Raman spectra. Intensity data from such work has been used to calculate electrooptical parameters for solid n-hydrocarbons (117). Morphology of isotropic and oriented linear polyethylene has been studied (118). Polymers can be investigated at high pressures (119).
D.n* J.
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RAMAN SPECTROMETRY
k a bchmr In mS b pamnsm Of m k b y at Newcasus upon l y r e P-nk. England. Hs was born in Ipswich, SUWOL. and recaked hk B.Sc. db see ham London UnivasW in 1988. Rrm. as a r-rch student at K W s collegs. C a m b W . he waked with James J. Tvner ~1 VlLwaIbnai spectroocop(c studbs of me oxygen fluaides. receiving h k Ph.D. w e e h 1971. He h n moved to Ywk univemily i *e. 811 a teachhg fellow. he waked wnh Ronald E. Hestw on Raman studies of MI- I ten SBH hydrates and nonaqueaus saiutions. AH* 2 years. he t d up hls present iectveship at Newcastb upan Tyne where he teaches physical-inorganic chsm(sby. HISresearch llnerests include Raman sMies of eiecvolvtes in nmqueaus soiuHons and IlqMs at presswe.
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A higb mure phase of polyethylene has been shown to have a liquifcrystal structure and high pressure spectra of poly(tetrafluoroethylene) have heen reported (120). Laatly, hy measuring monomer-polymer spectra, kinetic data on styrene polymerization have been obtained (121).
RAMAN MICROSCOPY Since the last review in this series, the Raman microprobe or MOLE (molecular optic laser examiner) and Raman mim c o in~general have been widely used to study a variety of microscopic samples. Many reviews descrihing the technique and applications of the micro robe have been published ( Z Z - I B ) . Sample preparation ant'handing techniques have been developed (129) and com uterized image processing systems have been used to engance image quality (130). Analysis of thin-layer chromatography fractions has been undertaken (131)and a somewhat simpler Raman spectrometer microscope attachment has been evaluated (132). The microprohe has been used extensively in geoscience (133)and in mineralogy. Studies of talc microparticles have provided estimates of intrasheet dipoledipole interactions (134)and its use in cement chemistry has been demonstrated (135). The microprobe is ideally suited to studies of inclusions in solids. Apatite in garnet, britholite, oligoclase, and monazite in sapphire, microline in beryl, and diopside in diamond and in peridote have been identified (136). Fluid inclusions can he studied (137). Analysis of organic material in fossil inclusions in rocks bas revealed the presence of asphaltites, amophous carbon, ester c=O groups, aliphatic hydrocarbons, aromatic compounds, and nitrogen containing groups (138-140). Quantitative analysis of CH,, CzH6,C,Hs, CO,, N,, and HzS in the gaseous phase of hydrocarbon rich fluid inclusions in minerals (141)further demonstrates the potenial of this technique. Particulate contaminations in s nthetic fibers can be identified (142) and subvisible BaJO. crystals have been detected in sealed glasa ampules of parenteral solutions (143). Other applications include studies of hydrosulfuration catalysts (144) and carbon fibers (145). The microprohe has also been used to characterize cellular inclusions (146-148) and to identify kidney stone components (149). Finally the possibilities of using the microprobe to provide valuable analytical data on semiconductor devices (150)and integrated circuits (151) look very promising.
THIN FILMS AND SURFACES Techniques having the ability to probe structure and comition of thin films and surfaces have wide applicability. an spectroscopy is now developing as a realistic tool in this field (152). Interference enhanced Raman scattering has allowed thin films (5Ck350 A), amorphous semiconducting material ( 1 5 3 , highly absorbing films (154) and Ti and Ti0, films (-6 nml ~~.(1551 . ~to he ~ examined ~ , and totnl ...- internnl ?e.. flert& methods nre also showing promise (156). Surface adsorbed HzO.CO,, and C,H, (1.57) and pnitrobenzoic acid (158)have been studied on alumina. Other adsorption studies include ethynylbenzene on zinc oxide (159),acetylene on titanium dioxide (1601, pyridine on molybdate (1611, ammonia (162) and organic bases (163) on silica, pyridine (164).bromine and iodine (165),sulfur dioxide (166),and nitrogen dioxide (167) on zeolites, unsaturated hydrocarbons on nickel and
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silver films (168),water on platinum (169),and carbon monoxide (170) and ethylene and deuterated ethylene (171) on silica supported nickel catalysts. The effect of annealing silica films (172) and the determinations of built-in streas in silicon films on sapphire (173) rovide examples of thin film studies. Silver(I1) oxide has e! en detected down to -10 monolayers (174)and the anodic oxidation of GaSh, GaP, and GaAs in annealed films has been investigated (175). Aqueous corrosion of lead (176,177) and oxide formation on lead electrodes ( 1 78) has also been followed. Oxide films formed on iron based alloys and steel have been characterized at thicknesas
