Electron spin resonance - Analytical Chemistry (ACS Publications)

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ANALYTICAL CHEMISTRY, VOL. 50, NO. 5, APRIL 1978

(268) Zmijewska, W., Chem. Anal. (Warsaw), 21, 853 (1976). (269) Foldzinska. A,, Dybczynski, R., J . Radioanal. Chem., 31, 89 (1976). (270) Rakovic, M., &hgdicova, A., P r o m , Z., Gregora, Z.,Radiochem. Radbanal. Lett., 24, 317 (1976). (271) Jiranek, V., Bludovsky, R., Collect. Czech. Chem. Commun., 41, 2690 (1976). (272) Anand, S. J., Radiochem. Radioanal. Lett., 27, 313 (1976). (273) Singh, E. R., Steinnes, E., Proc. Soil Sci. SOC. Am., 39, 370 (1975). (274) Lois Gonzaiez. M., Gonzaiez Portal. A,. Baluia Santos. C.. Ouim.. Anal.. 30, 307 (1976). (275) Yotsuyanagi, T., Yasrnashita, R., Hoshino, H., Aomura, K., %to, H., Masuda, N.. Anal. Chim. Acta, 82, 431 (1976). (276) Miller, R. G., Doerger, J., At. Absorp. Newsi., 14, 66 (1975). (2771 Jones. A. H.. Anal. Chem.. 48.,~ 1472 (19761. i278j Thomas, V. W., Jr., Kirby, L. J., Nelson, I . C., Rep. U.S. Energy Res. Dev. Admin., BNWL-SA-5480 (1975). (279) Folsom, T. R., Hansen, N., Weitz, W. E., Jr., Parks, G. J., Jr., Appl. Spectrosc., 29, 404 (1975). (280) Megarrity, R. G., Siebert, 8. D., Analyst (London), 102, 95 (1977). (281) Leoni, L., Braca. G., Sbrana, G., Giannetti, E., Anal. Chim. Acta, 80, 176 (1915). (282) Barela, T. D., Sherry, A. D., Anal. Biochem., 71, 351 (1976). (283) Franke, J. P., de Zeeuw, R. A., Pharm. Weekbl., I l l , 725 (1976). 87. (284) Maltseva, M. M., Pavlovskaya, N. A., Gig Sanit., 1976 (9, (285) Garcia Olmedo, R., Garcia Puertas, P., Salesa Perez, M.. Masoud, T. A,, Lis0 Rubio, F. J., An. Bromat., 28, 1 (1976). (286) Manolov, K., Stamatova, V., Matschev, A.. Mikrochim. Acta, 1976 (II), 343. (287) Porritt, R. E. J., Bowles, C. J., Kelly, J. W., Radiochem. Radioanal. Lett., 26, 27 (1976). (288) Minczewski, J., Chwastowska, J., Pham, T. H. M., Ana/yst(London), 100, 708 (1975). (289) Sokolov, D. N., Nesterenko, G. N., Zav. Lab., 42, 1172 (1976). (290) Mancini, C., Riv. Combust., 29, 91 (1975). (291) Handa, A. C., Johri, K. N., Indian J . Chem., A, 14, 294 (1976). (292) Schiller, P., Skalova, A., Chem. Zvesti. 29, 745 (1975). (293) Tzouwara-Karayanni, S. M., Microchem. J., 22, 259 (1977). (294) Postel, W., Goerg, A., Drawert, F., Guvenc, U., Brauwissenschaft., 28, 301 (1975). (295) Beavin, P., Jr., J . Assoc. Off. Anal. Chem., 59, 830 (1976). (296) Mishima, M., Jpn. Anal., 24, 433 (1975). (297) Koizumi, H., Yasuda. K., Anal. Chem., 48. 1178 (1976). (298) Alder, J. F., Alger, D.. Samuel, A. J., West, T. S., Anal. Chim. Acta, 81, 301 (1976). (299) Langmyhr, F. J., Lind, T., Jonsen, J., Anal. Chim. Acta, 80, 297 (1975). (300) Himmers. T. A., Fresenius’ Z . Anal. Chem., 277, 377 (1975). (301) Johnson, C. A., Anal. Chim. Acta, 81, 69 (1976). (302) Greiner, A. C., Chan, S. C., Nicoison, G. A., Clin. Chim. Acta, 61, 335 (1975). (303) Koirtyohann, S. R., Wallace, G.. Hinderberger, E., Can. J . Spectrosc., 21 (3), 61 (1976). (304) Julshamm, K., Braekkan, 0 . R., At. Absorp. Newsi., 14 (3), 49 (1975). (305) Slavin, S., Peterson, G. E., Lindahl, P. C., At. Absorp. News/., 14 (3). 57 (1975).

(306) Morris, N. M., Clarke, M. A., Tripp, V. W., Carpenter, F. G., J . Agric. Food Chem., 24, 45 (1976). (307) Fiorino, J. A., Jones, J. W., Capar, S. G., Anal. Chem.. 48, 120 (1976). (308) Tsutsumi, C.. Koizumi, H., Yoshikawa, S., Jpn. Anal., 25, 150 (1976). (309) Bielig, H. J., Dreyer, H., Treptow, H., fluess. Obst., 42, 369 (1975). (310) Acantini, C., de Berman, S. N., Colombo, O., Fondo, O., Reva Asoc. Bioquim. Argent., 40, 222 (1975). (311) Oiejko, J. T., J . A m . OilChem. Soc., 53, 460 (1976). (312) Korkisch, J., Huebner, H., Mikrochim. Acta, 1976 (11). 311. (313) Vondenhoff, T., Min. Bl. GDC-fachgr. Lebensminelchem. Gerichtl. Chem., 29, 341 (1975). (314) Andersson, A. Swed. J . Agric. Res., 6, 145 (1976). (315) Morris, N. M., Tripp, V. W., TAPPI, 59, 146 (1976). (316) Giovannini, E., Principato, G., Rondelli, F., Anal. Chem., 48, 1517 (1976). (317) Bail, D. F., Barber, M., Vossen, P. G. T., Sci. TotalEnviron., 4, 193 (1975). (318) Davis, E. A., Hui, K. S., Durden, D. A,, Boulton, A. A,, Biomed. Mass. Spectrom., 3, 71 (1976). (319) Nadkarni, R. A.. Morrison, G. H., Radiochem. Radioanal. Lett., 24, 103 (1976). (320) Cornelis, R., Speecke, A., Hoste, J., Anal. Chim. Acta, 78, 317 (1975). (321) Gaudy, A., Maziere, E., Comar, D., J. Radioanal. Chem., 29, 77 (1976). (322) Brune, D., Bivered, B., Anal. Chim. Acta, 85, 411 (1976). (323) Leonhard!, W., Niese, S., Jaross, W., Schentke, K., Meissner, D., Isotopenpraxs, 11, 130 (1975). (324) Scheihorn, !I., Pfrepper, G., Geisler, M., J . Radioanal. Chem., 33, 187 (1976). (325) Korshunov, Y. F., Zhuk, L. I., Orestova, I. I. Gureev, E. D., Kist, A. A,, Zh. Anal. Khim., 31, 1962 (1976). (326) Steinnes, E., Anal. Chim. Acta, 78, 307 (1975). (327) Haldar, B. C., Tejam, B. M., J . Radioanal. Chem., 33, 23 (1976). (328) Wyttenbach, A., Bajo, S.. Haekkinen, A., Beitr. Tabakforsch., 8, 247 (1976). (329) Dermelj, M.. Ravnik, V., Kosta, L., Radiochem. Radioanal. Lett., 28, 231 (1977). (330) Gosset, J., Bock, P., Engelmann, C., Analusis, 4, 161 (1976). (331) Boulton, R. B., Ewan, G. T., Anal. Chem., 49, 1297 (1977). (332) Fassel, V. A,, Peterson, C. A,, Abercrombie, F. N., Kniseiey. R. N., Anal. Chem., 48, 516 (1976). (333) Hsieh, S. A. K., Wong, G., Ma, T. S., Mikrochim. Acta, 1976 (11), 253. (334) Lapitskaya, S. K., Sviridenko, V. G., Palarnarchuk, A. S., Zh. Anal. Khim., 30, 629 (1975). (335) Camera, V., Giubileo, M., Euratom Rep., EUR 5407 (1975). (336) Widua, L., Geisert, K., Schieferdecker, H., Ber. Kernforschungszentrum Karisruhe, KFK-EXT-23/76-1 (1976). (337) Flint, R. W., Lawson, C. D., Standil, S., J . Lab. Clin. Med., 85, 155 (1975). (338) Purdham, J. T., Strausz, 0. P., Strausz, K. I., Anal. Chem., 47, 2030 (1975). (339) Cesareo, R., Eur. J . Nucl. Med., 1, 49 (1976). (340) Rabe, R., Landwirtsch. Forsch. Sonderh., 32, 186 (1976). (341) Hutton, J. T., Norrish, K., X-ray Spectrom., 6, 6, 12 (1977). (342) Williams, C., J . Sci. Food Agric., 27, 561 (1976). (343) Rethfeid, H., Crossmann, G., Egels, W., Landwirtsch. Forsch. Sonderh., 32, 251 (1976).

Electron Spin Resonance John R. Wasson” Ellestad Research Laboratories, Lithium Corporation of America, P.O.Box 795, Bessemer City, North Carolina 280 16

Peter J. Corvan Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 275 14

This review covers the published literature from July 1975 t o July 1977 although a few citations of other work are also included. As the previous reviewer observed (1) the volume of literature in which electron spin resonance (ESR) information is contained is too extensive for even brief citations in a review of this nature. However, it is hoped that the publications cited do provide a useful guide to recent developments and applications of ESR spectroscopy to chemical systems. The Chemical Society (London) Specialist Reports on ESR spectroscopy provide excellent comprehensive reviews of relatively recent publications and are recommended sources 0003-2700/78/0350-092R$O 1.OO/O

for beginning literature searches. Computer searching Chemical Abstracts and the new CA Selects-Electron Spin Resonance (Chemical Aspects) published by Chemical Abstracts Service, Columbus, Ohio 43210, provides convenient approaches to current awareness of the ESR literature. The thesis literature, covered by Dissertation Abstracts, continues to be a source of experimental procedures and details relevant to work in ESR spectroscopy.

BOOKS (2-27) AND REVIEWS The book edited by Ivin (8) contains worthwhile reviews of spin labels and probes in dynamic and structural studies C 1978 American Chemical Society


John R Wasson is a senior research chemist in the research department of Lithium Corpotation of America. He was born in St. Louis, Mo., and received his education at the Universlty of MissourrColumbla (B S , 1963, M A , 1966) and Illinois Institute of Technology (Ph D, 1970) H e is the author or co-author of more than 100 research papers, reviews, and technical articles His publications and interests are in the areas of magnetic resonance spectroscopy, transition metal and organometallic chemistry, and inorganic polymers and colloids. He is a member of the American Chemical Society, American Association for the Advancement of Science, The Chemical Society (London), Phi Lambda Upsilon, and

Table I. Reviews Subject

Sigma Xi

Peter J Corvan is currently a research associate at the University of North Carolina4hapel Hill. He was graduated from the University of Vermont with a B S degree in chemistrv in 1971 and will receive a Ph D degree frLm the State University of New York-Albany in early 1978 His research interests include synthetic inorganic and organometallic chemistry, magnetic resonance, transition metal macrocyclic compounds, and highly conducting materials He is a member of the American Chemical Society and Sigma XI

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of synthetic and modified polymers, ESR studies of spinlabeled synthetic polymers, and ESR studies of dynamic flexibility of molecular chains. Spin labels and nitroxide probes are covered rather comprehensively in the volumes by Likhtenshtein (15) and Berliner (16). The symposium volume edited by Resing and Wade (13) provides a survey of applications of magnetic resonance in colloid and interface science. A number of texts (14,22,23)present various aspects of ESR spectroscopy as employed in bio-inorganic chemistry. Review articles are listed in Table I. For convenience, the references for Table I are collected separately in the bibliography.

APPARATUS AND TECHNIQUES A simple inexpensive circuit has been described (25) which digitally converts the frequency of a n NMR gaussmeter to gauss. Conversion of a Varian E-3 spectrometer 100 kHz to 1 MHz modulation has been reported (26). A modification of a Varian E-3 spectrometer for detection of transient species generated by light flashes, e.g., from a pulsed nitrogen laser, has been described (27) and applied t o triplet phenazine in a single crystal of fluorene. An ESR spectrometer has been employed (28) as a novel specific detector for the liquid chromatography of stable free radicals. An inexpensive method of improving magnet performance in ESR spectrometers has been reported (29). Nonuniformities of the modulation field and the radiofrequency field alter the CW saturation behavior of inhomogeneously broadened ESR lines. Corrections to ESR saturation data have been considered (30), both theoretically and experimentally. The application of the discrete Fourier transform to ESR spectral data processing has been described (31). The ESR spectrum of [Cr(NH ) Cl]C12 diluted into the corresponding cobalt(II1) camp!:; powder a t 295 and 77 K has been recommended (32) for the calibration of the magnetic field over the range 1-6 kG. A new design for a cell t o make simultaneous electrochemical and ESR measurements has been reported (33) as has a cell for anaerobic transfer of biological samples for low-temperature ESR studies (34). A novel approach for obtaining ESR spectra of alkane and alkene radical cations consists (35) of irradiating the hydrocarbon of interest with cobalt-60 y-rays in a pentane matrix a t 77 K. A substantial amount of the positive ions formed by irradiation will then be trapped as radical cations of the additive. Fairly pure ESR spectra of the radical cations may subsequently be obtained by taking the difference by computer between the ESR spectra before and after selective removal of the radical cation by illumination

Spin-labeled fatty acids in membrane structures Radical anion in solution Steady state and time resolved ESR studies of radiolytically produced radicals Radical reactions Radiation chemical studies of halogenoand nitro- uracils Polymer radicals produced by mechanical destruction ESR and theoretical chemistry Organometallic radical anions Transition metal, lanthanide, and actinide ions in solids Simple rotamers Spin-labels in biophysics Saturation transfer ESR Mineralized tissues Membranesspin-label studies Hydrogen-bonded systems -ESR, ENDOR Surface analysis Simple free radicals Liquid crystals Phase transitions in SrTiO, and LaAlO, Relaxation in antiferromagnetic resonance Spin relaxation in fluids Line broadening Zeolites Ion-exchanger solvent system One- and two-dimensionalsystems Spin-labels, lipid-protein interactions Polyethylene photodegradation Point defects in solids Organic radicals Iron in natural compounds General

S = 2 3d" ions Analytical applications Impurities in gems Thermal detection of ESR Enzyme-metal ion-substrate complexes Biological molecules Electrochemistry and ESR Linebroadening and spin-spin relaxation near magnetic critical points Origin of electronic properties of molecules Donor-acceptor complexes in excited states Phosphotransferases Heterocyclic radicals Free radicals in solids produced by ionizing radiation Laser magnetic resonance spectroscopy Rare-earth and other impurity ions in noncubic sites Medicinal chemistry S-state ions High-temperature spin dynamics l'roteins and peptidesspin-labels Long-range proton hyperfine coupling Iron-sulfur proteins Magneto-microwave effects Copper(11) bis-chelates Solids Donor-acceptor complexes (65A) Polymeric metal complexes, catalytic activity ( 6 6 A ) with light of suitable wavelength. A capillary method of determining translational diffusion constants of ESR active species has been described (36) which has advantages over other methods. The glass transition temperatures of a number of polymers have been determined by the ESR spin-probe method (37) and compared with literature values. Plasma polymers have been shown (38) to contain radical concentrations which depend on the structure

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of the monomer and the nature of the plasma. The use of ESR to determine fluorine atom concentrations in chemical laser systems where F atoms and F, are present has been reported (39). The exchange broadening in the ESR spectra of nitroxide radicals by molecular oxygen has been employed (40) as a method of monitoring oxygen concentrations. The precision of quantitative ESR determination of copper(I1) on ion exchange resins has been evaluated (41) and new sample preparation techniques have been developed. A study of the uptake of copper(I1) by AN-31 anion exchanger shows (42) that [ C U ( R N H , ) ~ ( H ~ O )is ~ ]formed. *+ The determination of the composition of mixtures of sodium chromite and chromic oxide by ESR has been described in detail (43). A comparison of vanadium determinations in petroleum fractions by ESR and atomic absorption spectrometry gave a good agreement between the two approaches (44). The behavior and arrangement of Gachsaran residue in a magnetic field during the carbonization process has been investigated (45) using vanadylporphyrin chelates as spin-probes. Some of the chelates were incorporated into the mesophase formed with the molecular plane oriented parallel t o the field. The tar mesophase obtained during the carbonization of oil-cracking residues has also been characterized by ESR spectroscopy (46). An ESR study of the ash, smoke, and tobacco of cigarettes revealed the presence of manganese (47). A new procedure for the fast detection of narcotics in urine incorporating an ESR spin-label and a drug-specific antibody has been reported (48).

SPECTRAL ANALYSIS The interpretation of the ESR spectra of organic and inorganic radical species continues to undergo development and refinement. Indeed, the refinements in the analyses of ESR spectra have enabled the obtaining of more detailed information than many of the earlier workers thought possible. Although theoretical developments have made many things possible, it is fair to say that the widespread application of computer techniques has been the enabling factor. A general computer program for calculating the parameters of generalized and phenomenological spin-Hamiltonians from experimental ESR data has been described (50). The program will analyze ESR data sets consisting of any number of transition frequency-applied magnetic field pairs obtained at any combination of frequencies, applied magnetic fields, magnetic field-crystal symmetry axis orientation, and AM, = h l , * 2 , . . . transitions. A method for the computer analysis of ESR data which is particularly useful when the off-diagonal terms in the spin-Hamiltonian are large has been reported (52) and applied to data for Gd(II1) in SmC13.6Hz0. A quick, accurate procedure (least-squares fitting) for analysis of ESR data has been developed (52) and also applied to data for Gd(I1I) in SmC13.6H20. .4combined polynomial regression and nonderivative search technique for ESR spectral analysis, particularly for broad band spectra, has been described (53). Methods of analysis of the spectra of radicals having large hyperfine interactions have been presented (54) and the utility of the analyses in determining the relative signs of the hyperfine interactions has been pointed out. A simple method for the calculation of resonance fields of triplet ESR transitions has been given (55) which are the solutions of the cubic equation with coefficients depending on the parameters D and E . This approach is useful for the simulation of ESR powder spectra, A useful FORTRAN IV program for simulating single crystal ESR spectra has been made available (56). Effects of quadrupole interaction on two- and three-pulse electron spin-echo modulation patterns has been studied (57) by calculating the modulation patterns for model systems. The broadening of second-derivative Gaussian and Lorentzian absorption lines has been calculated (58) as a function of modulation amplitude. This work has a bearing on the identification of the dominant lineshape in the case of spectra with mixed lineshapes. An analysis of europium(I1) spinHamiltonian parameters has been presented (59) along with a comparison of corresponding parameters for gadolinium(II1) systems. The ambiguity problems of the spin-Hamiltonian have been discussed (60) and second- and third-order relaxation formulas derived in the case of isotropic random rotation. A method has been developed (61)to analyze ESR spectra for the case when the quadrupole coupling and the hyperfine coupling are

of comparable magnitudes but much smaller than the Zeeman term. The dependence of the energy eigenvalues on the various polyadics occurring in the generalized spin-Hamiltonian have been examined (62). A method of analyzing the ESR spectra of radical pairs, which makes it possible to separate Lorentzian and Gaussian components of the linewidth, as well as to determine the D values has been developed (63). A theory for understanding the positions and widths of lines in the ESR spectra of triradicals dissolved in anisotropic environments has been developed (64) for systems with rapid molecular reorientation. The qualitative reliability of Coulson’s equations linking the bond angle and orbital hybridization on the central atom of triatomic radicals, e.g., NO2, has been established using sophisticated MO methods (65). The ESR responses of inhomogeneously broadened electron spin systems have been considered in detail (66) under the assumption that a spin temperature situation in the rotating reference frame obtains in the constituent spin packets. Expressions have been derived for the rapid passage and slow passage responses of such systems, including situations where magnetic field modulation and subsequent phase sensitive first harmonic detection is employed. Theoretical and experimental work on dynamic nuclear polarization with an inhomogeneously broadened ESR line has been reported (67). A theory has been presented (68) for the electron spin-echo in nonviscous solution of radicals whose ESR linewidth is inhomogeneously broadened by unresolved intramolecular hyperfine structure. Electron spin-echo may prove useful for examining the relaxation of spin labels in solution. The utility of ESR calculations by the eigenfield method has been further demonstrated (69)and two FORTRAN IV programs for the calculations have been described.

ORGANIC RADICALS Studies of organic radical species continue to be the dominant application of ESR spectroscopy. Many elegant investigations of free radical kinetics, conformations, and reactivity are reported every year. Since McConnell’s initial spin label work in 1965 (70), spin label and spin probe techniques have been extensively employed in various biochemical and other applications. The books cited earlier afford comprehensive reviews of the uses of spin labels. The anisotropic ESR spectra of CF3X-(X = C1, Br, I) radical anions have been observed (72)following y-irradiation a t 77 K of solid solutions of the parent compound in tetramethylsilane (TMS), neopentane and 2-methyltetrahydrofuran. The spectral resolution was best in TMS. The perfluorobutane radical anion, prepared by y-irradiation of the title compound in neopentane, has uF of the same order as found in the hypervalent inorganic radical anions SF;, PF;, SF4-,and F3NO- (72). The methylsulfinyl radical, CH,SO, has been identified in a y-irradiated single crystal of dimethylsulfoxide (73) and its conformational dependence shown to follow a p,B cos20 relation. The tetrafluoroethylene radical anion (74)and its cycloaddition to the neutral molecule have been characterized. The g-values of 1,4-benzosemiquinoneand durosemiquinone anions in methanol, ethanol, and n-butanol have been measured a t temperatures above the freezing point of the solvents. The rapid variation of g with T i n the high viscosity region has been assigned to slow tumbling effects (75). Jones has reported (76)the strongly temperature dependent ESR spectrum of the [16]annulene radical anion. The temperature dependence arises from two sources: (a) the sigma-pi interaction parameter, Q H , is a function of temperature and (b) the spin-density distribution within the molecule is also dependent upon temperature. The g-tensor anisotropy of DPPH in DPPH, has been investigated (77) and found to be in agreement with earlier work (78). The free radical HC(=O)-CH2, among others formed by x- or y-ray irradiated crystalline deoxycytidine-5’-phosphate has been identified by ESR and ENDOR techniques (79). The strong influence exerted by the crystalline environment on radical reactions has been demonstrated in an ESR and ENDOR study of free radicals in X-irradiated barbituric acid (80). The unique sulfur-nitrogen heterocycle thiadiazolothiadiazole forms a radical anion upon alkali metal reduction in ethereal solvents (82). The properties and MO parameters for several similar species have been compared. A number of nitroaromatic, e.g., 4-cyanonitrobenzene, radical anions


enriched with carbon-13 a t positions 1 and 4 have been examined. Throughout the series of radicals studied, the 13C hyperfine splitting constant, QC,, depended largely on the spin density on nitrogen (82). The formation of peroxy radicals in y-irradiated poly(methy1 methacrylate) can be interpreted in terms of the solubility and diffusion of oxygen into the polymer samples (83). The reaction of tetracyanoethylene with magnesium in T H F yields the TCNE radical which is weakly bound to the metal ion via the nitrogen end of the radical (84). Pulse radiolysis of aqueous micelle solutions has been studied (85) by time-resolved ESR. Chemically induced dynamic electron polarization (CIDEP) was observed in the spectra of the alkyl radicals produced. Photolyses of solutions of 2,3-, 2 4 - , 2,5-, and 3,4-pyridinedicarboxylic acids containing isopropanol (and in some cases, acetone) with a high pressure mercury arc lamp afford 1-hydropyridinecarboxylateanion radicals (86). In the absence of acetone, the heterocyclic compound is excited and then abstracts a hydrogen atom from isopropanol to form the radical. The abstracted hydrogen usually, but not always, becomes attached to the ring nitrogen. In the presence of acetone the reduction involves excitation of the acetone molecule to form two molecules of the hydroxyisopropyl, (CH3)&OH, radical. This radical is capable of quickly reducing many heterocycles, e.g., pyridine, to radicals, likely as a result of electron transfer to the heterocycle followed by protonation of the ring nitrogen. The l-hydro-2,5-pyridinedicarboxylate anion radical has been shown (87) to undergo a reversible, base-catalyzed dissociation of the N-H hydrogen. Related radicals produced by one-electron reduction of nicotinic acid, nicotinamide, and methyl nicotinate have also been reported (88). The ESR spectra of the radical cations of polycyclic hydrocarbon carcinogens have been compared with MO calculations of radical rr-electron densities (89). The preferred structure of the triethylenediamine cation radical is apparently a symmetric one (90) rather than a dynamic equilibrium between classical asymmetric structures. Irradiation of butadiene and isobutene in the presence of VC14 yields the organic radical cations (91). In the presence of oxygen, peroxy radicals are formed in both systems. The phenoxy and cation radicals derived from 4-methoxy- and 4-ethoxy-2,3,5,6tetramethylphenol have been investigated and conformations, linewidth alternation, and steric and spin density effects on rotational barriers assessed (92). The cation radicals derived from a series of alkyl-substituted bis(4-hydroxypheny1)- and bis(4-methoxypheny1)sulfidesusing the reaction of the parent compound with AlC13 in nitromethane have been studied (93) and the ESR results are consistent with a helical conformation of the cation radical, the degree of helicity changing with the degree of alkyl substitution. The diaminodurene radical cation CH3

CH3

CH3

CH3

Lf

has been examined (94) in dimethylformamide solution as a function of temperature. While a&lH,showed a negligible dependence upon temperature, U G H and U N varied linearly and the results have been analyzed for restricted rotation of the amino groups. A value of 10.0 A 1.7 kJ/mol for the twofold barrier was obtained together with a value for QN of 2.03 0.8 mT(1T = lo4gauss). The radical cation and radical anion have of dithieno[3,4-b;3’,4’-e]paradithin-1,3,5,7-tetraone(DPT) been investigated (95).

*

0

0

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Valinomycin forms ion pair complexes with ammonium and alkali metal salts of tetracyanoethylene in benzene (97). Alkali metal ion pairs of the o-chloranil radical can be prepared by interacting o-chloranil in T H F or other solvent with the appropriate metal mirror. The structures, signs of coupling constants, hyperfine coupling constants and g-values of the species have been described (98). The interpretation of linewidth effects in the spectra of triple ions, e.g., those generated by alkali metal reduction of 1:4 quinones, has been developed (99) and applied to a number of representative systems. Two types of triplet excitons have been discovered (100) in K(TCNQ) crystals corresponding to two independent rows of TCNQ- ions in the lattice. The ESR spectrum of the dication of pheophytin has been examined (101). The zero-field splitting parameters for the T I state of the protonated pheophytin are D = 0.0288 i 0.0009 cm-’ and E = 0.0046 f 0.0001 cm-l. The application of electric field oriented nematic mixtures of cholesteryl chloride and cholesteryl laurate to the ESR spectroscopy of triplet organic species, e.g., naphthalene, has been detailed (102). The single crystal spectra of the radical salt 3,3’-diethyl-Z,2’-selenacyanine[TCNQI2exhibit a linewidth dependence well represented by AH(0) = ( ~ (cos2 3 0 -1)’ p sin40 where 0 is the angle between the applied magnetic field direction and the normal to the magnetic layers in the system; (Y and p are temperature dependent parameters (103). The 2,Z‘-oxacyanine analogue has also been studied (104). Frequency-swept absorption ELDOR signals for the CH2COO- radical in zinc acetate depend upon Zeeman modulation frequency, the signals going from a positive to a negative sense as the Zeeman modulation frequency is varied from 100 to 1 kHz. A model for such behavior has been developed (105). Conformation dependence of y-proton coupling has been studied (106) on the basis of the hyperfine tensors determined by ENDOR for the three methyl protons of CH3CH(N+D3)COOD-trapped in an irradiated crystal of L-alanine. Photolysis of aqueous cadmium sulfide dispersions gives rise to the formation of the superoxide anion as demonstrated by trapping the 02-with 5,5-dimethyl-l-pyrroline-l-oxide(DMPO) (107). The synthesis and ESR spectra of a series of benzimidazole-3-oxyl-1-oxide free radicals has been described (108).

+

0

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I

? If computer techniques for spectral analysis are employed, the radicals can be used as spin labels. The ESR spectrum of the fluorinated nitroxide biradical CF3N(0.)CF2CF2N(O.)CF3 has been obtained on the pure liquid and in solution. When the pure liquid is rapidly frozen in liquid nitrogen, it forms a purple glass and its spectrum exhibits the .Ud, = fl and rt2 transitions of the triplet state. Upon warming the sample undergoes a phase transition at -140 “C to a yellow polycrystalline solid which is diamagnetic (109). The ESR spectra of the axial isomer of the steroid spin label 3doxyl-5a-cholestane has been obtained by computer subtraction of the equatorial isomer from a partially purified mixture of the two isomers. Analogous spin labels have also been prepared and characterized (110). An analysis of the ESR spectrum of the cholestane spin label in oriented bilayers of lecithin and cholesterol in the gel state have been reported (111). Monoamine oxidase can be determined (112) using spin labeled p-hydroxyamphetamine as a probe for the active site. The chlorpromazine radical cation (CH 2)3N M e 2

Satellite lines from naturally abundant I7O, 33S,and I3C have been detected. A simple MO model accounts very well for the properties of the radical ions. Correlations between long range coupling constants in ESR and NMR have been examined (96).

gg)@cl in oriented fibers of DNA pulled from a gel yields data explained in terms of a strongly immobilized label having one principal hyperfine tensor axis parallel to the axis of the DNA helix and the preferential orientation of the ions with their

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planes parallel to the DNA helical axis (113). The use of spin labels to determine polymer transition temperatures has to be performed with some caution. Increasing probe size can result in increasing transition temperatures (114). Di-tertbutyl nitroxide has been employed (115) as a probe for studying water and aqueous solutions. Zeolites exchanged with spin labels containing a cationic group have been investigated to obtain information on active sites and adsorbed species (116). Analytical expressions for the forms of the ESR spectra of a nitroxyl radical in the region of "slow rotations" (IO+ 2 T I lO-'s; T is the rotational correlation time) have been derived (117) and the effect of the degree of nonsphericity on the determination of average rotation frequencies in a model of a spherical radical has been analyzed. Analytical expressions for ESR lineshapes in the slow-rotation region have been obtained (118) for a symmetrical top nitroxyl radical using the adiabatic approximation and an arbitrary jump model. A study of the ordering and spin relaxation in a liquid crystalline solvent has been reported (119) in which perdeuterated Tempone was employed as the probe. Spin-lattice relaxation times (Z'J of the simple nitroxides 1-0xyl-2,2,6,6-tetramethyl-4-hydroxypiperidine (tanol), perdeutero-1oxyl-2,2,6,6-tetramethyl-4-piperidone (tanone), and 15Nsubstituted tanone have been measured (120) in sec-butyl benzene from +30 - -85 "C. At the highest temperatures, spin-rotation may be the dominant relaxation mechanism but a t all other temperatures relaxation rates are substantially shorter than predicted by known mechanisms. The type of analysis necessary to extract the Heisenberg exchange frequency of nitroxide radicals in solution whose ESR spectra are complicated by inhomogeneous broadening due to intramolecular proton hyperfine interactions has been discussed (121). ESR lineshape analysis of a partially oriented collection of long and essentially cylindrically symmetrical species has been described (122) in connection with the theoretical simulation of the ESR spectra of fibers of DNA spin labeled with the radical cation of chlorpromazine. The AMI = 0 ELDOR spectra of nitroxide radicals in amorphous polystyrene and polypropylene matrices display absorptions at Au = 13.5 and 27 MHz. The intensities of these signals are decreased by about 35% in perdeuterated polystyrene. This and the frequency establishes the signals to be matrix ELDOR which results when nonbonded protons interact with the resultant of the external field and the electronic field (123). ELDOR studies of a variety of nitroxide radicals have been employed (124) to discriminate between translational and rotational correlation times in liquids.

PARAMAGNETIC INORGANIC MATERIALS y-Irradiation of boron trifluoride in TMS affords the BF, radical (125) which had previously been claimed in irradiated NaBF4 The ESR parameters for BF; are in accord with those of the isoelectronic radicals CF3, NF3-, and FzNO. Phosphoranyl radicals, generated by y-irradiation of phosphorus compounds, have been extensively examined (126) and their electronic structures elucidated and substituent effects assessed. y-Irradiation of SF6 a t -196 "c yields SF, and SF6radicals-the latter can be removed by annealing a t -137 "C. The ClV SF5radical has -50% of the total spin density in the 2p, orbitals of the equatorial fluorines with the remainder in the sulfur 3s and 3p, orbitals (127). ?-Irradiation of BrF, in SF6affords the BrF6 radical (128). The F3NO- radical can be similarly prepared (129) as can be ClF6 (130). The dimer radical cation of dimethylselenide has been identified in a y-irradiated single crystal of the parent compound, its main ESR spectrum showing hyperfine coupling with 1 2 equivalent hydrogens (131). The irradiation of hexagonal BN with 550-kV electrons results (132) in a 3-boron center and consists of an electron trapped in a nitrogen ion vacancy. Photolysis of solid trifluoramine oxide, F3N0, at -196 "C produces the F2N0 radical for which the ESR data suggest a pyramidal structure (133). The interaction of elemental sulfur-33 with a partially hydroxylated MgO surface gives rise to the S; radical (134). The original analysis of the data for S has been modified using CNDO/SP calculations for both and S3- (135). Unusual spin resonance observations made on a sample of rare earth ion exchanged Y-zeolite have been attributed (136) to the presence of a ferromagnetic impurity and have been qualitatively explained in terms of the nonlinear behavior in

g3+

ferromagnetic resonance a t high power. XeCl in argon a t 4.2 K shows g - 1.962 and g 2.303. The g shifts relative to XeF are b i s e expected hu: to increased halogen spin-orbit coupling interaction and/or decreased chemical bonding on going from XeF to XeCl(137). y-Irradiation of triphenylphosphineborane yields the Ph3PBH2 radical (138) while y-irradiation of crystals of KPF6 containing traces of AsF6- gives the AsF,- radical (139). The laser magnetic resonance spectra of the NH2 radical have been measured (140) by using 15 far-IR frequencies and the results compared with those obtained using other techniques. The 85Rb-87Rbhyperfine structure anomaly for Rb atomic-like impurity states in a solid OP(NMeJ3 matrix has been investigated (141). ESR and other techniques have been employed in the characterization of inorganic ion-exchangers of the zirconium phosphate type, ZrM(P0&*4H20 (M = divalent metal ion) (142). X-ray irradiated calcium hydroxide exhibits an 0- center which in alkaline earth oxides is also known as a V- center (143). The ESR spectrum of 170-labeledNO3,- radical ions formed by y-irradiation of KN3 crystals doped with the l70-enriched potassium nitrate exhibits axial symmetry (144). ?-Irradiation of NaN03 enriched with 170-nitrateions yields the spectrum of neutral NO3 which has no observable nitrogen hyperfine splitting. It was suggested (145) that the NO3 radicals occupy sites of the parent nitrate ions in the crystals and are rapidly rotating about their C3 symmetry axis. X-irradiation of crystals of KHS04 leads to the formation of SO; and species identified as SO3- and SOz- (146). Se02- type radicals have been identified in single crystal and powder samples of yirradiated LiH3(Se03)2and LiD3(Se0& (147). The use of ESR line broadening to obtain chemically interesting information has undergone an initial development (148) which has been applied to studies of the dimerization of copper(I1) dithiocarbamates in a variety of solvents (148),the clustering of manganese ions in Mn(I1)-doped BaC12.2H20(149),and the concentration dependence of the ESR linewidths of Cu(I1) in diamagnetic powdered Ni(I1) diethyldithiocarbamate (150). The approach developed has also been employed to examine dipolar broadening of free radicals and to determine the number of free radicals in cigarette smoke (151). The optical detection of ESR of excited states in silver halides has been reported (152) as has a PdC1,'- center in a silver chloride crystal (153). Mixed AgCl-NaCl crystals y-irradiated at 77 K yield spectra which have been interpreted (154) as arising from Aj(I1) centers and a center associated with Ag(1) clusters. Ag, centers in photochromic glasses have been described (155). Paramagnetic IrCls4- and IrBrk- have been identified (156) as products of the light-induced decomposition of Ir(II1)-doped AgCl and AgBr single crystals. Ag(I1) centers, AgBrCli- and AgBr2Clt-, have been detected in AgBr,Cl,-, crystals a t helium temperatures (157). ENDOR experiments on Ti(I1) doped in CaF, afford covalency parameters for the TiFS6 center (158). The effect of an applied electric field on the ESR spectrum of Mn(I1) in SrC1, has been measured at 77 K (159). The electric field effect, which shows axial symmetry about the crystallographic (111)axes, can be explained by a displacement of the Mn(I1) ion along (111) directions. ESR spectra of Mn(I1) in the tetrahedral sites of the spinels CdY2S, and CdYzSe4as a function of temperature have been reported (160). A comparison with other compounds shows that the Mn hyperfine splitting depends u on the anionic environment and increases in the order Se2-, and 0,- which corresponds to a decrease of the covalent contribution to the chemical bonding. The powder spectra of Mn(4-methylpyridine N-oxide)6(C104)2 doped into the corresponding zinc, cadmium, and mercury compounds have been described (161) and the advantages of exact diagonalization of the spin-Hamiltonian matrix and multiple frequency studies pointed out. Isotropic g-values and hyperfine splitting constants for I4N of bis(dithiooxalato)nitrosyliron(I) have been determined in 16 solvents (162). Electron spin relaxation mechanisms and solvent coordination were assessed. ESR studies of high-spin Fe(II1) tetraphenylporphines having orthorhombic distortions have been presented (163) along with an improved method of interpretation. Crystals of Na4[(FeEDTA),0].12H20 have been studied, the spectra analyzed, and the exchange pa202 f 10 cm-l has been determined (164). A rameter J simple method has been presented for calculating the pa-

&,

-


rameters of the hole model for distorted octahedral low-spin t,: complexes (165). Explicit derivations of the expressions necessary to analyze the ESR spectra of low-spin heme iron centers have been described (166). A method for deriving a spin-Hamiltonian which describes ligand hyperfine structure of isolated Paramagnetic centers has been developed (167) and applied to ENDOR data for high-spin heme proteins. Planar low-spin CON#, Schiff base chromophores have been investigated (168) and it was concluded that the unpaired electron resides in a d orbital on the metal. The ESR spectrum of low-spin Eo(BPT), bis[l-methyl-3-(2-chloro6-methyl)phenyltriazine-l-oxide]cobalt(II),in crystalline Ni(BPT) exhibits very high intensity MI = =k1 and f 2 forbidden hyperfine lines. The cobalt nuclear quadrupole moment, derived from analysis of the spectrum, is one of the highest reported (169). Palladium(1) and -(III) centers have been characterized (170) in y-irradiated ammonium chloride single crystals doped with palladium(I1). The spectra of Rh2+ impurity centers in 170-enrichedMgO have yielded information about the behavior of this Jahn-Teller ion and covalency parameters (171). The ESR strain parameters of cubic Gd(II1) in CaF, have been measured using the ultrasonic strain modulation technique (UMER) in which 40-kHz strain modulation replaces the magnetic field modulation in conventional ESR (172). The x-band spectra of U(V) in tetragonal centers in NaF and LiF show that the effects of the nuclear quadrupole interaction are stronger than those of the magnetic hyperfine interaction (173). An analytical method for determining the parameters was developed. The triplet spectra of nine binuclear exchange-coupled vanadyl(1V) complexes have been reported (174) and the zero-field splitting parameter D related to the metal-metal separation. A paramagnetic center interacting with matrix protons gives rise to proton spin-flip transitions which lead to satellite lines in ESR spectra. The relative microwave power saturation behavior of allowed “main” and “forbidden” satellite transitions has been examined in Cu-63 doped CaCd(acetate),6H20 and PO?- in y-irradiated Na2HPO3.5H20single crystals. Differences in saturation can be explained semiquantitatively by the differential saturation theory of Shimizu (175). In basic (pH >12) solution Cu(I1) forms a soluble complex which has been formulated as planar Cu(OH),’- (176). The K-band spectra of 170-labeledCu(I1) oxinate and picolinate have been reported (177). The Jahn-Teller effect in Cu(I1)-doped hexaimidazolezinc(I1) dichloride tetrahydrate has been examined (178). A t 77 K the one-ion-per-unit-cell spectrum is indicative of tunneling between the three Jahn-Teller configurations. The structure and single crystal ESR spectra of Cu(imidaz~le),(NO~)~ have been described (179). Spin-lattice relaxation for Cu(I1) in nickel(I1) diethyldithiocarbamate has been treated theoretically and experimentally with reasonable agreement between the two (180). Single crystal ESR studies of six-coordinate bis(w-nitrophenonato)bis(4-methylpyridine)copper(II) in the corresponding zinc(I1) chelate have been reported (181). The calculations of the covalency parameters by means of the conventional LCAO-MO approach, based on metal hyperfine data, gives unreliable results. X-band ESR Faraday and Cotton-Mouton-Voigt effects in polycrystalline CuC1,.2Hz0 and (NH,),CU(SO~)~-GH~O have been described (182). A one-dimensional, spin-diffusive model has been employed (183) to account for the single crystal ESR data for N,N’-bis(trifluoroacetylacetone)ethylenediiminecopper(II). Dimeric C U ~ C ~in, ~[ -C 0 ( e n ) ~ ] ~ C u ~ C l ~ C 1 ~has . 2 Hbeen , 0 examined (184) a t X-, K- and Q-band frequencies a t selected temperatures in the range 2-77 K. The triplet species and the interdimer exchange frequency have been characterized. The weak exchange and dimensionality of CaCu,Cdl.,(1I x I0.9) has been probed by an ESR study (OAC)~.~H,O of single crystals and lineshape analysis (185). Copper(I1) porphin has been studied in single-crystal and polycrystalline triphenylene. The data are consistent with copper porphin replacing triphenylene molecules substitutionally (186). The ESR spectra of Cu(II)-DL-valine and DL-methioninecomplexes have been recorded in the solid state and solution. Kivelson’s theory was employed to explain the hyperfine linewidth in solution (187). Polymeric bis(d1-aaminobutyrat0)- and bis(1-asparaginato)copper(II) do not exhibit spin-exchange to 1.8 K (188) and the metal-ligand covalency is rather minimal. Time-averaged and other ESR data as well as 63Cu enrichment has contributed to the

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characterization of galactose oxidase (189). Copper cytochrome c has been shown to be six coordinate (190). Single crystal studies of Cu-doped dipiperidylthiouram disulfide and tetramethylthiouram disulfide have been interpreted (191) in terms of planar and tetrahedral coordination sites, respectively. ESR spectra have been employed (192) to obtain nuclear quadrupole coupling constants for copper in six square planar complexes, five with sulfur donors and one having both oxygen and sulfur donor atoms. The ESR data for Cu(I1)suLfur donor complexes have been surveyed (193) in connection with the relation of such data to the determination of the binding sites in the “blue” copper proteins. Pseudotetrahedral copper(I1) complexes have been extensively examined (193-195). Reference 195 contains an expanded listing of data for such compounds. A number of pseudotetrahedral Cu(I1) complexes exhibit novel single line solution spectra due to the small magnitude of the isotropic hyperfine coupling constant. It has been noted (194,195) that the “blue” copper proteins, if they could yield isotropic solution spectra, would have hyperfine coupling constants in the range -20-40 X lo4 cm-’, Le., they would exhibit only single line spectra.

NOMENCLATURE FOR ESR SPECTROMETRY We have compiled the following list of terms, their definitions, and abbreviations, which occur most frequently in papers on ESR spectrometry. The list is not complete and some of the definitions have been somewhat oversimplified. Anisotropic motion. Preferred rotation about one axis of a paramagnetic species. Anisotropy. Variation of a property with direction of the applied magnetic field. Axial symmetry. Obtains when a species has one %fold or higher order rotation axis. Bimodular cauity. .4microwave cavity which can be subjected to two microwave frequencies simultaneously. Cavity wavemeter. Device for measuring the microwave frequency. Delocalized. Implies that the unpaired electron density is spread over several atoms. Diamagnetic. Possessing no net electron magnetic moment. Dielectric absorption. Strong microwave field absorption by polar liquids, especially water. Such samples are said to be very “lossy”. Dipolar correlation time. The time taken for a spin system to rotate through one radian from its previous orientation due to “through space” interactions with neighboring spins. Dipolar interaction. Magnetic interaction between two magnetic moments by virtue of the effect of the magnetic field of one on the other. Electron s p i n resonance(ESR) spectrometry. Also called electron paramagnetic resonance(EPR) spectroscopy. The study of magnetic dipoles of electronic origin by applying (usually) fixed microwave frequencies to a sample residing in a varying magnetic field. Exchange coupled. Interaction of unpaired electrons associated with different sites. The energy of the interaction is characterized by the exchange integral, J . Flat cell. Quartz sample cell with flat faces -0.3 mm apart, commonly employed for solutions in polar liquids. Gauss ( G ) . Strictly speaking, a unit of magnetic induction while the oersted (oe) is a unit of magnetic field intensity. The practical equivalence of the two units has led to the common usage of the gauss as the unit of magnetic field intensity. 1 kG = 103G. 1 Tesla (T) = 104G. Gaussian lineshape. Shape of a spectral line whose hei ht as a function of frequency v is given by Z(v) = 1- exp[-b B(vo - v ) ~where ] vo is the frequency of the line center and the linewidth is Av = 2(ln 2)’j2/b. g-Value. Factor which expresses the size of the magnetic moment of a paramagnetic species; frequently, it is only a phenomenological parameter. The basic resonance condition is given by: hv = g/3H where h is Planck’s constant, I’ is the microwave frequency, g is the dimensionless g-value (or spectroscopic splitting factor), /3 is the Bohr magneton, and H is the applied field a t which resonant absorption occurs. Hall probe. Magnetic field measuring device employed for stabilizing the field of electromagnets. Hertz (Hz). Frequency of one cycle per second (cps). 1 GHz = 109 HZ.

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Hyperfine splitting. Splittings in the lines of an ESR spectrum arising from the interaction of the unpaired electron with nuclei in the vicinity. Interaction (dipolar) broadening. Concentration-dependent broadening of ESR lines resulting from magnetic interactions between paramagnetic species. Isotropic. A property which is the same independent of direction of the applied magnetic field. Isotropic spectrum. ESR spectrum in which the overall molecular tumbling is so rapid that all anisotropy in the spectrum is averaged out. Linewidth. The width of a spectral line, normally defined as the distance (in gauss) between the two points of half maximum height, i.e., the peak-to-peak separation in a first-derivative spectrum. Lorentzian lineshape. Shape of a spectral line whose hei ht as a function of frequency Y is given by I(v) = I - / [ l aB( y o - Y ) ~ where ] vo is the frequency of the line center and the linewidth is AY = 2 / a . Microwave. Electromagnetic radiation with frequencies of the order of 1O'O Hz = 10 GHz(-3 cm wavelength). Modulation. Superposition of a varying wavelike component onto some steady quantity, e.g., magnetic field modulation; introduction of a small component of the magnetic field whose direction varies with time in a wavelike manner a t a particular frequency. Orbital magnetic moment. Magnetic moment of an electron which is associated with its orbiting motion around a nucleus (or nuclei) in an atom or molecule. This magnetic moment is in addition to the spin magnetic moment. Paramagnetic. Possessing a net electron magnetic moment, Le., a t least one unpaired electron. Powder spectrum. ESR spectrum in which the molecular axes (and principal axes) have completely random orientations with respect to the applied magnetic field, as in a powder or frozen solution. The powder spectrum consists of the superposition of all the individual spectra from all the different orientations. Principal axes. The three independent directions (of the magnetic field) along which the g-value, or hyperfine interaction, has its minimum or maximum values. These values are the "principal values" of the g- or hyperfine tensors. Relaxation. Process by which an atom or molecule is an excited state falls back into its ground state. Saturation. Situation in which the rates of upward and downward energy level transitions induced by radiation are equal, so that no net energy is absorbed. S p i n density. The fraction of unpaired electron spin which is in the vicinity of a particular nucleus in the molecule. Spin-lattice relaxation time, TI. A measure of the time taken for the spin population t o return to its equilibrium value through interaction with fluctuating internal fields which surround it (the lattice). Spin-spin relaxation time, T,. A measure of the time to lose phase coherence, i.e., return to equilibrium through interaction with neighboring spins. It is inversely proportional to the linewidth. Spin-Hamiltonian. Quantum mechanical formalism employed for determining the energy levels of an unpaired electron. Spin-label. Stable free radical used as an environmental probe molecule. Spin-polarization. Mechanism by which unpaired electron spin on one atom or part of a molecule is transferred to another atom. This is accomplished by interaction between the unpaired electron and the paired electrons on the second atom. Superhyperfine splitting. Hyperfine splitting in the ESR spectrum of a transition metal ion caused by interaction with the ligand nuclei. Triplet states. Energy levels generated by two unpaired electrons which interact. Zero-field splitting. Occurs when the degeneracy of energy levels from paramagnetic species with S > l / z is split by the internal crystalline electric field present in the absence of an applied magnetic field.

+

ACKNOWLEDGMENT The authors gratefully acknowledge the support and encouragement of Professor William E. Hatfield of the Univ-

ersity of North Carolina-Chapel Hill. LITERATURE CITED

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99R

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Phys., 14, 327 (1976). (178) P. S. Rao and S. Subramanian, J . Magn. Reson., 22, 191 (1976). (179) D. L. McFadden, A. T. McPhail, C. D. Garner, and F. E. Mabbs. J . Chem. Soc.. Dalton Trans., 47 (1976). (180) L. K. Aminov, R. Kirmse, and B. V. Solovev, Phys. Status SolidiB, 77, 505 (1976). (181) D. Attanasio, J . Magn. Reson., 26, 81 (1977). (182) Y. Servant, J. C. Bissey, and S. Gharbage, ibid., 24, 335 (1976). (183) M. I.Scullane and H. C. Allen, Jr., ibid., 26, 119 (1977). (184) K. T. McGregor and W. E. Hatfield, J . Chem. Phys., 65, 4155 (1976). (185) R. Gaura, R. Adams, et al., J . Magn. Reson., 25, 299 (1977). (186) J. Bohandy and B. F. Kim, ibid., 28, 341 (1977). (187) B. N. Misra and S. D. Sharma, ibid., 24, 1 (1976). (188) H. W. Richardson, J. R. Wasson, W. E. Estes, and W. E. Hatfield, Inorg. Chim. Acta, 23, 205 (1977). (189) R. D. Bereman and D. J. Kosman, J . Am. Chem. Soc., 99, 7322 (1977). (190) M. C. Findhy. L. C. Dickinson. and J. C. W. Chien, ibid., 99, 5168 (1977). (191) R. A. Palmer, W. C. Tennant, M. F. Dix, and A. D. Rae, J . Chem. Soc.. Dalton Trans., 2345 (1976). (192) U. Sakaguchi and A. W. Addison, J . Am. Chem. SOC.,99, 5189 (1977). (193) H. Yokoi and A. W. Addison, Inorg Chem., 16, 1341 (1977). (194) J. R. Wasson, D. M. Klassen, H. W. Richardson, and W. E. Hatfield, ibid., 16, 1906 (1977). (195) J. R. Wasson, H. W. Richardson, and W. E. Hatfield, Z . Naturforsch. 6 , 32, 551 (1977). Literature for Table I (1A) J. Seelig, Biomembranes, 3, 267 (1972). (2A) N. Hirota, Int. Rev. Sci.: Phys. Chem. Ser. Two, 4, 85 (1975). (3A) R. W. Fessenden in "Fast Processes Radiat. Chem. Biol.. Proc. L. H. Gray Conf., 5th, 1973", G. E. Adams, E. M. Fielden, and B. D. Michael, Ed., Wiley. New York, N.Y., 1975, pp 60-75. (4A) P. B. Ayscough. T. E. English, and D. A. Tong, ibid., pp 76-81. (5A) P. Neta, ibid., pp 235-40. (6A) J. Sohma and M. Sakaguchi, Adv. Polym. Sci., 20, 109 (1976). (7A) P. T. Narasimhan, J . Sci. Ind. Res., 35, 11 (1976). (8A) P. R. Jones, Adv. Organomefal. Chem., 15, 273 (1977). (9A) H. A. Buckmaster and D. B. Delay, Magn. Reson. Rev., 4, 63 (1976). (10A) J. A. Ladd and H. W. Wardale in "Internal Rotation of Molecules", W. J. Orville-Thomas, Ed., Wiley, New York, N.Y., 1974, pp 115-55. (11A) F. Axel, Biophys. Struct. Mech., 2, 181 (1976). (12A) D. D. Thomas, Trends Biochem. Sci., 2, N62 (1977). (13A) K. Ostrowski and A. Dziedzic, "Biochem. Physiol. Bone, 2nd ed", G. H. Bourne, Ed., Academic Press, New York, N.Y., 1976, Vol. 4, p 303. (14A) B. J. Gaffney and S. C. Chen, Methods Membr. Bid., 8, 291 (1977). (15A) R. Blinc in "Hydrogen Bond", P. Schuster, G. Zundel, and C. Sandorfy, Ed.. North-Holland, Amsterdam, 1976 Vol. 2, p 831.

lOOR

ANALYTICAL CHEMISTRY, VOL. 50, NO.

5, APRIL 1978

(16A) J. H. Lundsford, Crit. Rev. Solid State Sci., 6, 337 (1976). (17A) T. A. Miller, Ann. Rev. Phys. Chem., 27, 127 (1976). (18A) M. Schara, “Proc. Int. Sch. Phys. “Enrico Fermi”, 1973”, pp 638-55, publ. 1976. (19A) K. A. Mueller, ibid., pp 201-54. (20A) H. Gasparoux and J. Prost, Ann. Rev. Phys. Chem., 27, 175 (1976). (21A) S.M. Rezende, AIP Conf. Proc., 34, 1 (1976). (22A) H. Gabriel, Hyperfine Interact., 2, 91 (1976). (23A) G. Fischer, Top. Curr. Chem., 66, 115 (1976). (24A) P. H. Kasai, ACS Monograph, 171, 350 (1976). (25A) M. I.loktev and A. A. Slinkin, Usp. Khim., 45, 1594 (1976). (26A) G. S.Bystrov, G. A. Grigor’eva, and N. I.Nikolaev, iba., 45, 1621 (1976). (27A) P. M. Richards, Ref. 18A, p 539. (28A) W. T. Roubal, Progr. Chem. fats Other Lipids, 13, 61 (1973). (29A) P. F. Kane and G. B. Larrabee, Anal. Chem., 49, 221R (1977). (30A) K. Tsuji, Am. Chem. Soc., Div. Org. Coat. Plast. Chem. Pap., 3 5 , 167 (1975). (31A) G. D. Watkins in “Point Defects in Solids”, J. H. Crawford, Jr., and L. M. Slifkin, Ed., Plenum, New York, N.Y., 1975, VoI. 2, p 333. (32A) B. Gaffney and C. McNamee, Methods Enzymol., 32, Part B, 161 (1974). (33A) F. Baer, A. Berndt, and K. Dimroth, Chem. Unserer Zeit, 9, 18, 35 (1975). (34A) W. Oosterhuis, Struct. Bonding, 20, 59 (1974). (35A) J. Smith in “Mod. Phys. Tech. Mater. Technoi.”, T. Mutvey and R. Webster, Ed., Oxford University Press, 1974, p 291. (36A) C. Rudowicz, Acta Phys. Pol., A47, 305 (1975). (37A) B. Flockhart, Proc. SOC. Anal. Chem., 9, 134 (1972). (38A) C. Scala, Aust. Gemmol., 12, 119 (1974). (39A) W. More, Pure Appl. Chem., 40, 211 (1974). (40A) 0. Shaltiel, At. Energy Rev., 12, 699 (1974). (41A) J. Villafranca, Met. Ions. Bioi. Systems, 4, 29 (1974). (42A) M. Rak, Biochemie, 57, 483 (1975). (43A) P. Sullivan, Magn. Reson. Rev., 3, 251 (1974).

(44A) K. Hauser, “Methodicum Chimicum”, F. Korte, Ed., Academic Press, New York, N.Y., 1974, Vol. 1, F’t. A, pp 318, 375. (45A) B. Kastening, Adv. Anal. Chem. Instrum., 10, 421 (1974). (46A) P. Narasimhan, J. Indian Chem. Soc., 52, 275 (1975). (47A) M. Seehra and D. Huber. AIP Conf. Proc., 1974, 24, 261 (1975). (48A) R. McWeeny in “Orbital Theory of Molecules and Solids”, N. Marsh, Ed., Oxford University Press, 1974, p 199. (49A) S.Nagakura, Excited States, 2, 321 (1975). (50A) M. Cohn, Ciba found. Symp.. 31, 87 (1975). (51A) B. Gilbert, Phys. Methods Heterocycl. Chem., 6, 95 (1974). (52A) H. Shields, Magn. Reson. Rev., 3, 375 (1974). (53A) K. Evenson and C. Howard, “Laser Spectrosc., Proc. Int. Conf. 1973”, R. Brewer and A. Mooradian, Ed., NTIS. Springfield, Va., 1974, p 539. (54A) J. Baker in “Cryst. Fluorite Structure”, W. Hayes, Ed., Oxford University Press, 1974, p 341. (55A) 0. Williams-Smith and S.Wyard, Prog. Med. Chem., 12, 191 (1975). (56A) D. Newman and W. Urban, Adv. Phys., 24, 793 (1975). (57A) P. Richards, NATO Adv. Study Inst. Ser., Ser. B , 7, 147 (1975). (56A) P. Knowles, Amino-Acids, Pept., Proteins, 7, 196 (1976). (59A) F. King, Chem. Rev., 76, 157 (1976). (60A) W. Orme-Johnson and R. Sands, “Iron-Sulfur Proteins”. W. Lovenberg, Ed., Academic Press, New York, N.Y., 1973, Vol. 2, p 195. (61A) Y. Servant, Magn. Reson. Rev., 4, l(1975). (62A) A. Shklyaev and V. Anufrienko, Zh. Strukt. Khim., 16, 1082 (1975). (63A) D. L. Beveridge in “Semiempirical Methods of Electronic Structure Calculation: Part B: Applications”, G. A. Segal, Ed., Plenum Press, New York, N.Y., 1977, Chap. 5. (64A) P. H. Kasai in “Solid State Chemistry and Physics”, P. F. Welier, Ed., M. Dekker, New York, N.Y., 1973, Chap. 6. (65A) 2. G. Suos and D. J. Klein in “Treatise on Solid State Chemistry”, N. B. Hannay, Ed., Plenum, New York, N.Y., Vol. 3, 1976, Chap. 9. (66A) E. Tsuchida and H. Nishida, Adv. Polym. Chem., 24, 1 (1977).

Emission Spectroscopy Ramon M. Barnes Department of Chemistry, GRC Tower 1, University of Massachusetts, Amherst, Massachusetts 0 1003

This 16th article in the series of biennial reviews of emission spectroscopy surveys with emphasis and format employed previously (2A)the emission spectrochemical literature appearing in refereed publications during 1976 and 1977. Books and eneral reviews of emission spectroscopy and closely relate$ subjects are considered in the first section, whereas specific reviews and texts are included in each of the five topical sections. Spectral descriptions and classifications are examined in the second section. An abbreviated instrumentation section follows, and standards, samples, calibrations, and calculations are evaluated in the fourth section. The emphasis on excitation sources reflects the size of section five. In the sixth section, important applications are explored.

BOOKS AND REVIEWS A number of excellent books and reviews of emission spectroscopy appeared during the past two years. Maintaining their position as the major sourcebooks for atomic spectrochemical analysis, the 5th and 6th volumes of “Annual Reports on Analytical Atomic Spectroscopy” continue to provide yearly review and commentary on published and conference activities in atomic absorption, emission, and fluorescence spectroscopy during 1975 and 1976 (13A,14A). These timely volumes consider all major emission and absorption instrumentation and applications. A 1977 supplement to the ASTM “Methods for Emission Spectrochemical Analysis” was published (IA), as were the plenary and invited lectures from the XVIIIth and XXth Colloquium Spectroscopicum Internationale edited by Robin (32A)and Rubeska et al. (33A),respectively. Of the recent books, Schrenk‘s text “Analytical Atomic Spectroscopy” includes instrumentation, procedures, and applications for combustion and electrical sources in spectrochemical analysis suitable for advanced undergraduate and beginning graduate students (34A).In contrast, Epstein’s practical monograph “Chemical Analysis by Emission Spectroscopy” is oriented toward technicians or hobbyists

(IOA).

0003-2700/78/0350-10OR$05.00/0

In “Trace Analysis: Spectroscopic Methods for Elements”, editor Winefordner combines chapters on optical, x-ray, nuclear, and mass spectroscopic methods into a comprehensive reference source (43A).In addition to the chapters on atomic spectroscopic methods written by Veillon (39A),and optical instrumentation by Elser (9A),O’Haver (25A,26A) d’iscusses sample handlin and other analytical considerations. Barnes e d i t e j a unique book, “Emission Spectroscopy”, consisting of 39 reprinted papers, patents, or excerpts from benchmark publications in emission spectroscopy during the past century complemented by an extensive and comprehensive bibliography and editorial commentary (3A).This volume provides an in-depth view of emission spectroscopy beginning before Kirchhoff and Bunsen, and covers developments in qualitative and quantitative emission spectroscopy, as well as the progress in the design and understanding of electrically generated excitation sources which range from arc and spark to high frequency plasmas. In keeping with the spirit of the American Revolution bicentennial celebration, Laitinen and Ewing included in “A History of Analytical Chemistry” a fascinating chapter on analytical spectroscopy opening with atomic spectroscopy (21A).Walsh also reviewed the progress in spectrochemistry during the past century (41A).Walker (40A)and Klinkenberg (19A)prepared chapters on atomic spectroscopy, while James (36A),Kantor (18A),and Pinta (30A)published chapters on emission spectroscopy. Laqua (22A)presented an excellent overall review of optical emission spectrochemical applications, and Winefordner et al. (42A)critically reviewed multielement atomic spectroscopic methods. Fike et al. (11A)considered some properties of flames and electrical discharges in high-temperature atomic and molecular spectroscopy, and Hastie (15A)discussed plasmas in “High Temperature Vapors”. Among translations, “Spectrochemical Analysis” by Torok et al. (37A)is available in an up-dated version of the 1974 Hungarian original. In “Spectrochemical Analysis of Pure

D 1978 American Chemical Society

Electron spin resonance - Analytical Chemistry (ACS Publications)

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