5 Part (ii) INFRARED AND RAMAN SPECTROSCOPY By D. A. Long (School of Chemistry University of Bradford) FACED with the task of reviewing a field in which over three thousand papers were published last year this reporter finds himself somewhat in sympathy with one of Oscar Wilde’s maxims,’ ‘It is a sad thing that nowadays there is so little useless information’. There is of course implicit in this sentiment an acknowledgment of the value of so much that has been published. Perhaps this admission will serve as a general apology to those whose recent contribu-tions to spectroscopy have not survived the whims of personal selection or the restrictions on space. The new-style Annual Report requires in the language of the art phil-osopher a movement from realism towards idealism and expressionism.The varied nature of this particular subject has not lent itself to portrayal entirely in the new style and while for some topics a bold and no doubt subjective selection has been made for others an unashamedly detailed survey seemed more appropriate. The three thousand or so abstracts covering this field for the year 1968 may be compared with the mere eight hundred or so that it was necessary to survey for the two-year period 1962-1963 when preparing an earlier Annual Report2 on this topic. Although the year under review has seen no dramatically new advance in i.r. and Raman spectroscopy the continued expansion of the number of publications in this field is adequate testament to its value and interest for the chemist. The number of papers reporting Ranian spectroscopic studies is growing rapidly reflecting the impact that gas laser sources have made in this field.Lasers continuously tuneable over a limited frequency range are now available and it is an exciting prospect that CW lasers continuously tuneable over the whole visible region may become available for Raman spectroscopy. The potential applications of existing gas lasers to some aspects of Raman spec-troscopy have yet to be exploited. The study of rotational and vibration-rotation Raman spectra under high resolution and the Raman spectra of matrix-isolated species are two examples. The ease with which good quality Raman spectra can now be obtained from a minute amount of sample (which no longer needs to be colourless) will lead to Raman spectroscopy playing a role fully complementary to that at present enjoyed by i.r.spectroscopy in the laboratory of the analytical and preparative chemist particularly the inorganic Oscar Wilde ‘Complete Works,’ Collins London 1966 p. 1203. D. A. Long Atirr. Reports 1963. 8 84 D. A. Long chemist. A demand will soon be created for a laser-Raman instrument of modest price and intermediate performance. It is disappointing to have to record that the intriguing phenomena produced by giant-pulse lasers namely the stimulated inverse and hyper Raman effects have received little attention from chemists although they all open up novel possibilities. Several books and numerous reviews whose subject matter falls in the general field of i.r. and Raman spectroscopy have appeared.Only a limited and necessarily somewhat pcrsonal selection can be mentioned here. Schuler3 has written a review of Raman spectroscopy and lasers which includes a good coverage of the stimulated Raman effect. The excellent bibliography deals Rot only with the normal and stimulated Raman effects but also normal and stimulated Brillouin scattering and self-trapping. Bloembergen4 has written an authoritative review of the stimulated Raman effect and other phenomena which arise from the nonlinear third-order polarisation in the electric field strength. A survey of multiphoton spectroscopy byPetticolas5 includes aspects of the stimulated inverse and hyper Raman effects. A monograph entitled ‘Quantum Electronics’ by Yariv6 deals with the theoretical background to lasers and nonlinear optics.Adams7 has published a valuable critical survey of the i.r. and Raman spectra of metallic and organometallic compounds. Metal-halogen vibrational frequencies,8 far 4.r. spectros~opy,~ and i.r. spectroscopylO of aqueous solutions have all been the subject of reviews. Solid-state Studies.-The solid state is certainly the state of matter most frequently investigated by i.r. and Raman spectroscopy. The gas laser used in conjunction with a double monochromator makes it extremely easy to obtain the Raman spectra of solid compounds and a feature of the past year has been the substantial increase in Raman studies of the solid state. Excellent Raman spectra may be obtained from a minute amount of solid sample contained, for example in an ordinary melting-point tube and placed at the focus of a laser beam.Raman spectroscopy of solids is well on the way to becoming as routine an operation for the chemist as i.r. spectroscopy and will prove no less valuable. Indeed since low-lying frequencies are more easily obtained, Raman spectroscopy may often prove more valuable for the inorganic chemist. Where single crystals are available the laser makes it possible to illuminate along a given crystal axis with a defined state of polarisation and measure the intensity of Raman scattering essentially at right angles for each plane of polarisation. Systematic variation of the directions of illumination and 3 C. J. Schuler ‘Laser-Induced Spontaneous and Stimulated Raman Scattering,’ in Progress in Nidear Energy Series I X ed.H. A. Elion and 0. C. Stewart Pergamon Press, Oxford 1968 vol. 8 part 2. * N. Bloembergen Amer. J . Phys. 1967 25 989. 13 A. Yariv ’Quantum Electronics,’ John Wiley and Sons New Ynrk 1967. W. L. Petticolas Ann. Rev. Phys. Chenr. 1967 18 2 3 3 . D. M. Adams ‘Metal-Ligand and Related Vibrations,’ Arccjld London 1967. R . J. H. Clark Halogen Chenr. 1967 3 8 5 . J. W. Brasch Y. Mikawa and R . J. Jakobsen Appl. Spectroscopic Rep. 1968 1 187. lo F. S. Parker Progr. Infrared Spectroscopy 1967 3 75 Part (ii) Irlfuarcd and Hariiarz Spectroscopy 85 observation and the plane of polarisation of the incident beam enables the scattering tensor to be determined for each vibration. An unambiguous assignment of frequencies to symmetry classes can then usually be made.Measurements of this kind made previously using mercury-arc excitation were not only extremely laborious to obtain but usually inaccurate as a result of convergence errors and the ill-defined state of polarisation of the incident beam. The application of laser-Raman spectroscopy to single-crystal studies was pioneered by Porto and his co-workers.ll Their study of calcite has shown that the anomalies found by many previous workers are attributable to imperfect experimental procedure; it is salutory to note in passing that these anomalies had been given sophisticated theoretical explanations by a number of people. A recent paper12 discusses in detail the chemical applications of singlc-crystal Raman spectroscopy and shows that it can lead to unambiguous assignments whereas polarisation measurements on liquids or solutions (assuming a suitable solvent to be available) usually do not; e.g.polarisation measurements on an octahedral species MX6 in solution will distinguish v1 from v2 and v5 but v2 and v5 cannot themselves be unambiguously dis-tinguished in this way. Beattie and Gilson report single-crystal studies of KzPtC16 KzPdC16 KzSnC16 CSzGeCl6 and (NH4)sTeCb (all with octahedral anions) and K2PdC14 and (NH4)2PtC14 (square-planar anions) which coilfirm previous assignments. Other systems investigated were mercury(1) chloride, cassiterite anatase rutile gallium trichloride aluminium tribromide and molybdenum trioxide. The method relies on the validity of predictions of the Raman scattering tensor resulting from factor group analysis.The procedure is not without its complications and many pitfalls can beset the unwary. These include birefringence crystal imperfection dichroism the resonance Ramaii effect twinning enantiomorphism and internal reflection. The use of isotopic substitution and the examination of spectra at different temperatures can make valuable contributions to Raman studies of oriented single crystals. A recent typical example is the work of Rousseau et on Na14N03 and Na15N03. Earlier investigations of the Raman spectrum of sodium nitrate had revealed apparent anomalies in the scattering tensors for some modes and had left the assignments of the external modes in doubt. Using a laser source these workers found that apart from small intensity contributions in some orientations which are probably due to depolarisation effects arising from the birefringence of the crystal; the polarisability tensors of both internal and external modes are in accord with the selection rules.By comparing the spectra of Nal4N03 and Na15N03 they were able to assign the two external modes unambiguously. One of these is a libration and the other a translation of the NO- ion. A pure libration should show no nitrogen-l 1 S. P. S. Porto J. A. Giordmaine and T. C . Damen Phys. Rev. 1966 147 608: S. P. S. Porto P. A. Fleury and T. C . Damen Phys. Rev. 1967 154 522. I. R . Beattie and T. R. Gilson Proc. Roy. Soc. 1968 A 307 407. l3 D. L. Rousseau R. E. Miller and G. E. Leroi J . Cheni. Phys. 1968 48 3409 86 D. A . Long isotope independence since the centre of gravity of the NO; remains un-changed during the vibration whereas the translation should exhibit a shift.The calculated shift is small and is not observable at normal temperatures since the two lines are broad. Cooling to 35°K produced sufficient sharpening of these lines to reveal a frequency shift of the right order between Nal4N03 and Na15N03 for one frequency (98 cm.-l) and not the other (185 cm.-l). A brief selection of other crystals whose Raman spectra have been studied includes naphthalene anthracene,14 tungstates molybdates,l5 and rhombic sulphur.16 Ferroelectric materials have also been much investigated by both i.r. and Raman spectroscopy. Recent studies include BaTi03,17 NaN02,lS glycine silver nitrate,lg triglycine sulphate,20 potassium dihydrogen phos-phate,21 and SbSI.22 Raman spectroscopy has been proposed as a valuable method of studying transitions in solids,23 e.g.the of the Raman spectrum of a single crystal of SrTiO3 down to 2 5 " ~ . The results for a nominally pure single crystal are in accord with an ideal cubic perovskite structure (point group Oh) at higher temperatures with a transition at 110"~ to a tetragonal phase most probably C 4 h or D 4 h . Both phases show no first-order Raman scattering. An impure crystal undergoes different phase transitions as the temperature is reduced; it is probably tetragonal at 7 8 " ~ with point group S4 C4 or C 4 v and changes to a crystal structure of lower symmetry than tetragonal at lower temperatures. A selection of other spectroscopic studies of phase changes merit mention.Sodium nitrate shows a A transition at 267.7"~ when long-range order dis-appears. In the ordered structure the Raman-active totally symmetric stretching mode of the nitrate is i.r.-inactive but it is permitted for the lower site symmetry of the disordered lattice. The intensity of v1 in the i.r. can there-fore serve as a qualitative measure of short-range order. An i.r. over the temperature range 150"-300"c shows a band in the correct frequency range whose intensity variation with temperature is in accord with the vanish-ing of long-range order but gives no sharp change in short-range order in the transition region. The laser-excited Raman spectrum of crystalline quartz has 14 M. Suzuki T. Yokoyama and M. Ito Spectrochim.Acta 1968 24 A 1091; C. H. Ting J. Chinese Chem. SOC. Formosa 1967 14 1 17. ls R. K. Khanna W. S. Brower B. R. Guscott and E. R. Lippincott J. Res. Nut. Bur. Stand. Sect A. 1968 72 81. 16 A. T. Ward J. Phys. Chem. 1968 72 744. 17 M. DiDomenico jun. S. H. Wemple S. P. S. Porto and R . P. Bauman Phys. Rev., 1968,174,522 ; M. DiDomenico jun. S. P. S. Porto and S. H. Wemple Phys. Rev. Letters, 1967 19 855; D. L. Rousseau and S. P. S. Porto Phys. Rev. Letters 1968 20 1354. 18 E. V. Chisler and M. S. Shur Izvest. Akad. Nauk S.S.S.R. Ser.$z. 1967 31 1098. 19 P. S. Narayanan and A. V. R. Warrier Proc. 1st Internat. Conf. Spectroscopy Bom-20 I. Savatinova and P. Simova Optika i Spektrraskopiya 1968 24 218. 21 M. S . Shur Izvest. Akad. Nauk S.S.S.R. Ser.jiz. 1967 31 1042. 22 R. Bline M. Mali and A. Novak Solid State Comm. 1968 6 327. 23 R. Loudon Adu. Phys. 1964 13 423. 24 W. G. Nilson and J. G. Skinner J. Chem. Phys. 1968 48 2240. 35 W. L. Craft and L. J. Slutsky J. Chem. Phys. 1968 49 638. bay 1967 2 312 Part (ii) Infrared and Raman Spectroscopy 87 been studied26 over the temperature range - 196 to 615"c. A weak mode of A1 symmetry with a room-temperature Raman shift of 147 cm.-l grows in intensity and moves towards zero Raman shift as the a-p phase transition is approached. This mode clearly plays a fundamental role in the phase transi-tion but a full explanation could not be given. 1.r. and Raman ~pectroscopy~~ have been used to study the red to yellow phase transition in mercuric iodide for which the transition temperature at normal pressure is 127"c.Raman spectroscopy28 was employed to show that at normal temperatures and pressures in excess of 13 kilobars the red form of mercury(n) iodide changes to the yellow form with a spectrum identical with that obtained above 127"c at normal pressure. Schutte and Heyns29 have reported a series of low-temp-erature i.r. studies of structural changes with phase transitions in several ammonium salts. For example they find that in (NH4)2Cr207 free rotation of NH4f is indicated above 2 6 8 " ~ but this becomes hindered at lower tempera-tures. The transitions liquid-+solid I+sslid I1 in CF4 have been studied by i.r. and Raman spectros~opy.~~ Phase I appears to be a plastic crystal. The influence of external factors on the spectra of crystals has been the subject of some interesting studies.In their paraelectric phases (Oh) the first-order Raman spectrum is forbidden for SrTi03 and KTa03 but an electric field applied along a (001) direction induces C4v symmetry and renders all the phonons first-order Raman-a~tive.~~ ScotP2 has shown that the Bu modes of Caw04 and CaMo04 which are both i.r. and Raman-inactive in unstrained material become i.r. active and exhibit Eu characteristics under xz or y z shear strain and Au characteristics under xy shear strain. Such effects must be taken into account in interpretation of previously published i.r. spectra from crystals which may not be strain-free. Raman studies of polariton spectra have recently assumed importance. Polaritons arise in polar crystals from photon-phonon interactions.They give rise to Raman shifts in the scattering in the near-forward direction. The frequency shift is zero in the forward scattering direction but increases as the angle between the direction of observation and the forward direction varies over a small range typically 0.6-3.4". Raman scattering from polaritons was first observed by Henry and H ~ p f i e l d ~ ~ in GaP and subsequently in 211034 z6 S. M. Shapiro D. C. O'Shea and H. Z. Cummins Phys. Rev. Letters 1967,19 361. 27 A. J. Melveger R. K. Khanna B. R. Guscott and E. R. Lippincott Inorg. Chem., 1968 7 1630. 28 J. W. Brasch A. J. Melveger and E. R. Lippincott Chem. Phys. Letters 1968 2, 99; C. Postmus V. A. Maroni J. R. Ferraro and S. S. Mitra Inorg. Nuclear Chern.Letters 1968 4 269. 29 C. J. H. Schutte and A. M. Heyns Chem. Phys. Letters 1967,1,487; C. J. H. Schutte and A. M. Heyns ibid. 1968 1 511 515; C. J. H. Schutte ibid. p. 585. 30 R. P. Fournier R. Savoie F. Bessette and A. Cabana J . Chem. Phys. 1968 49, 1159. 31 P. A. Fleury and J. M. Worlock Phys. Rev. 1968 172,613; R. T. Schaufele M. J. Weber and B. D. Silverman Phys. Letters 1967 25 47. 32 J. F. Scott J . Chem. Phys. 1968,48 874. 33 C. H. Henry and J. J. Hopfield Phys. Rev. Letters 1965 15 964. 34 S. P. S. Porto B. Tell and T. C. Damen Phys. Rev. Letters 1966,16,450 88 D. A. Long and quartz35 by Porto and his co-workers. The theory of polariton spectra has been the subject of several recent papers.36 The importance of polariton spectra stems from their potential as tuneable sources of radiation.Such a source could be afforded by the angular dependence of the frequency of spontaneous Raman scattering involving polaritons but it would be of very low intensity. However stimulated Raman scattering involving polaritons would provide a tuneable source which was intense and coherent. It should be remarked that the ability to observe Raman scattering from polaritons, involving as it does observations so close to the forward direction is a striking example of the unique value of the laser for Raman investigations. Such observations could not have been made with conventional sources. The Raman spectra of the semi-conductors G ~ A s ~ ~ GaSe,38 and InSb39 have been studied and interpreted. Phonon dispersion curves for various silicon carbide polytypes have been plotted from Raman spectra data.40 Second-order Raman spectra of the alkali-metal halides are now being reinvestigated with laser excitation.Using a helium-neon laser and a double inonochromator the second-order Raman spectrum (0-400 cm.-l) of NaCl can be directly recorded in 20 min. whereas Toronto mercury arc excitation required a 48 hr. exposure a striking example of the revolution wrought by lasers. Recent studies include NaCl4I and KI.42 A theoretical ~tudy4~ has been made of the second-order Raman spectrum of CsF. Two different assumptions about the polarisability tensor lead to predicted spectra which while they are distinguishable experimentally have in common the unusual feature that they consist almost entirely of very sharp clearly separated lines.1.r. studies include NaC144 and LiF.45 It is interesting to note that two papers46 report that when gas lasers are focussed into LiF or NaCl single crystals lines attributable to multiple phonon processes are observed. The theory of the Raman effect in metals has received attention.47 Raman scattering from Be and AuA12 has been studied.48 In a Raman of 35 S. P. S. Porto Phys. Rev. 1967 162 834; J. F. Scott and S. P. S. Porto ibid. 161, 903. 36 E. Burstein S. Ushioda and A. Pinczuk Solidstate Comm. 1968,6,407; R . Ruppin and R. Englman J . Phys. (C) 1968,1,630; R . Fuchs and K . L. Kliewer J. Opt. SOC. Amer., 1968 58 319. 37 B. Tell and R . M. Martin Phys. Rec. 1968 167 381. 38 J. L. Brebner R. Loudon J. P. Russell and C.T. Sennett Proc. 1st Internat. Conf. Spectroscopy Bombay 1967 2 507. 39 J. Pons-Corbeau and J. Jouffroy Bull. SOP. Frartc. Mineral. Cristallogrphie 1967, 90 498. 40 D. W. Feldman J. H.Parker jun. W. J. Choyke and L. Patrick Phys. Reu. 1968, 173 787. 41 M. Krauzman Compt. rend. 1968 266 B 186. 42 M. Krauzman Compt. rend. 1967 265 B 689. 43 J. R. Hardy and A. M. Karo Phys. Rev. 1968 168 1054. 44 T. Kubota K. Hisano and 0. Matumura J . Phys. SOC. Japan 1968,25,642. 45 Z . G. Akhvlediani Izuest. Akad. Nauk S.S.S.R. Ser. $z. 1968 32 37. 413 G. Heilmann Z . Phys. 1968,215,43 1 ; G. Heilmann Z . Phys. ibid. 214,402. 47 D. L. Mills A. A. Maradudin and E. Burstein Phys. Reil. Letters 1968 21 1178. 48 D. W. Feldman J. H. Parker jun. and M. Ashkin Phys. Rev.Letters 1968,21 607. 49 A. Pinczuk and E. Burstein Phys. Rev. Letters 1968 21 1073 Part (ii) Infrared and Ranian Spectroscopy 89 InSb surfaces surface electric field-induced and resonance-enhanced Raman scattering from LO phonons has been observed and leads the authors to suggest that surface electronic properties may be studied by Raman spectro-scopy. The theory of Raman scattering from solids has been the subject of several papers.50 The interesting field of i.r. and Raman spectra induced or modified by impurities in crystals continues to grow. The introduction of impurities into the lattice of alkali-metal halides will modify the vibrations of the whole crystal lattice and may produce local or quasi-local vibrations associated with changes in the motion of neighbouring atoms.There have been interesting developments in the Raman spectroscopy of such crystals Stekhanov and E1iashberg5I reported the observation of quasi-local vibrations in the Raman spectra of KCl with Br- I- or Li+ impurities (0.1-0-5 mole %) the most characteristic feature being a strong line around 200 cm.-l. Stekhanov and Mak~imova~~ also reported quasi-local vibrations in the Raman spectra of KC1 doped with Na+ Cs+ or Rb+ (0-54-7 mole 7;). Recently Kaiser and MOckeP carried out a careful study of the Raman spectra of extremely pure KC1 and KC1 doped with 0.7 mole % KI. They found no trace of a line around 200 cm.-l and no evidence for an impurity-induced first-order Raman effect. They did find a Raman line at ca. 212 cm.-l in KCl :I- ( 0 3 %) coloured by exposure to a cobalt source.Since Stekhanov et al. had noticed that the mercury arc used in their experiments coloured the crystals it was concluded that the line at 212 cm.-l is associated with a colour centre in a doped crystal. Observations of Raman scattering from colour centres in pure crystals have been reported by Worlock and port^,^^ but there is no evidence for strong sharp localised modes of vibration. However, in KCl-KBr mixed crystals (20-80% KCl) a first-order spectrum has been reported by Porto et al.,55 the main feature of which is a band in the region 120-155 cm.-l of Alg symmetry. A first-order impurity-induced Raman spectrum has also been reported56 for KL with 2 mole % KN02. The theory of first-order Raman scattering by substitutional defects in alkali-metal halides has been treated by Benedik and Nardelli.57 There have been many i.r.studies of impurity-induced spectra. The following selected list of publications representative of the kinds of systems investigated shows how wide ranging these studies are U centres (H-50 A. K. Ganguly and J. L. Birman Phys. Rev. 1967 162 806; C. H. Ting Spectro-rhim. Acta 1968 24 A 1177; M. Hass and H. B. Rosenstock Appl. Optics 1967 6 , 2079; J. R. Hardy ‘Phonons Perfect Lattices Lattices Point Imperfections,’ Scot. Univ. 6th Summer School 1965,245; J. C. Decius J . Chem. Phys. 1968,49 1387. j1 A. I. Stekhanov and M. B. Eliashberg Soviet Phys. Solid State 1965 6 1 1 . 52 A. I. Stekhanov and T. I. Maksimora Soviet Phys. Solid State 1966 8 737. 53 R. Kaiser and P.Moeckel Phys. Letters 1967 25 749. 54 J. M. Worlock and S. P. S. Porto Phys. Rev. Letters 1965 15 697. 56 1. W. Shepherd A. R. Evans and D. B. Fitchen Phys. Letters 1968,27 171. 57 G. Benedek and G. F. Nardelli Phys. Rev. 1967 154 872. J. P. Hurrell S. P. S. Porto T. C. Damen and S. Mascarenhas Phys. Letters 1968, 26 194 90 D. A. Long impurity) in alkali-metal halides;58 rare-earth doped and hydrogenated CaFz showing spectra characteristic of rare-earth +HA ion pairs;5g OH- and OD-in alkali-nietal halides;60 atomic hydrogen in CaF2;61 BH4- and NH4f in alkali-metal halides;62 divalent anion and cation impurities in KCl;63 0 2 - in KBr;64 BO; in alkali-metal halides;65 CO;- NOS NO, and CO in alkali-metal halides;66 ZnS with Cu A1 or Ag A1;G7 silicon doped with boron and lithium;6s NaCl doped with AgCl and CuCl;69 simple mass defect effects resulting from natural 35Cl and 37Cl isotopic abundance in NaCl and LiF;70 the effect of an electric field71 on Li-doped KBr.The theory of impurity-induced i.r. spectra has also attracted attention.72 An interesting application of solid-state Raman spectra has recently been made by Bernstein and co-~orkers.~~ They have observed the vibrational frequency of 0,- in seven different alkali-metal halide hosts. The observed frequency varies with the host lattice. Plots of voo (the 0-0 electronic transi-tion frequency) us. the vibrational frequencyof 0,- are linear for a given cation and the lines for all cations intersect at the same point which corresponds to voo and the vibrational frequency for the free 0,- ion.The i.r. spectra of the various forms of ice have been studied.74 75 High-resolution Studies.-The study under high resolution of rotational and 58 D. Baeuerle and B. Fritz Phys. Status Solidi 1967 24 207; X. X. Nguyen Phys Rev. 1967 163 896; J. B. Page jun. and B. G. Dick Pliys. Rev. 1967 163 910; D Baeuerle and B. Fritz Solid State Comm. 1968 6 453. 59 S. Yatsiv S. Peled S. Rosenwaks and G. D. Jones Opt. Properties Ions Cryst., Conf. 1966 409. 6O A. I. Stekhanov and T. I. Maksimova Fiz. Tverd. Tela 1967 9 3668; M. L. Meist-rich U.S. Clearinghouse Fed. Sci. Tech. Inform. 1967; R. G. Grisar K. P. Reiners, K. F. Renk and L. Genzel Phys. Status Solidi 1967 23 613; M. E. Bauer and W. R. Salzman Phys. Rev. Letters 1967 18 590.61 R. E. Shamu W. M. Hartman and E. L. Yasaitis Plzys. Rev. 1968 170 822. 62 E. H. Coker and B. H. Campbell Proc. S. Dakota Acad. Sci. 1965 44 128; E. H. 63 D. N. Mirlin and I. 1. Reshina Fiz. Tverd. Tela 1968 10 1129. 64 0. Sild Eesti NSV Tead. Akad. Toim. 1968 17 203. 65 T. Mauring Eesti NSV Tead. Akad. Toim. 1968 17 232. 66 M. S. Pidzirailo and I. M. Khalimonova Ukrain. fiz. Zhur. 1967 12 1063; R. Metselaar and J. van der Elsken Phys. Rev. 1968,165 359; W. A. Morgan E. Silberman, and H. W. Morgan Spectrochim. Acta 1967 23 A 2855. 67 H. Kukimoto S. Shinonoya T. Koda and R. Hioki J. Phys. and Chem. Solids, 1968 29 935. 68 M. Balkanski J. Phys. (Paris) Colloq. 1967 2 8 , 69 R. Weber and F. Siebert 2. Phys. 1968 213 273. 70 M. V. Klein and H. F. Macdonald Phys.Rev. Letters 1968 20 1031. 71 R. D. Kirby and A. J. Severs Solid State Comm. 1968 6 613. 72 G. Benedek and A. A. Maradudin J. Phys. and Chem. Solids 1968 29 423; S. Takeno Progr. Theor. Phys. 1967 38 995; V. G . Koval'chuk Ukrain. fiz. Zhur. 1968, 13 437; T. C. Tak U.S. Atomic Energy Comm. 1967 Nuclear Sci. Abstr. 1967 21, 47027; T. P. Martin Phys. Rev. 1968 170 779. 73 J. Rolfe W. Holzer W. F. Murphy and H. J. Bernstein J. Chem. Phys. 1968 49, 963; W. Holzer W. F. Murphy H. J. Bernstein and J. Rolfe J. Mol. Spectroscopy 1968, 26 543. Coker and D. E. Hofer J. Chem. Phys. 1968 48 2713. 74 E. Whalley and J. E. Bertie J. Colloid Interface Sci. 1967 25 161. 75 J. E. Bertie H. J. Labbe and E. Whalley J. Chem. Phys. 1968,49 775; J. E. Bertie. H . J. Labbe and E.Whalley ibid. p. 2141 Part (ii) Infrared and Raman Spectroscopy 91 vibration-rotation spectra is a very important source of structural information yielding rotational and centrifugal distortion constants in the ground and excited vibrational states Coriolis coefficients anharmonicity constants etc. High-resolution i.r. spectroscopy is a well-developed technique but the selection rules are such that some molecules can only be studied by Raman spectroscopy. Even where i.r. spectroscopy is also applicable the selection rules are not identical with those for Raman spectroscopy and by and large, the Raman bands contain more information than the corresponding i.r. bands. Unfortunately experimental difficulties have in the past severely limited the experimental study of Raman spectra under high resolution.There was an important period of activity in this field in the 1950s when development of improved mercury lamps and mirror-type Raman cells with multiple cone collection made possible a series of elegant studies mainly by Welsh and S t ~ i c h e f f ~ ~ and their collaborators. The natural linewidth of the 4398 8, Hg line is ca. 0.2 cm.-l and so it is not possible to study with mercury-arc excitation systems with rotational spacings less than this; indeed the practical limit has been 0.245 cm.-1. Consequently this period of activity came to an end in the main when those relatively few molecules to which this limitation did not apply had all been studied. Other limitations were that the sample must be colourless and available in litre quantities.Thus as one author has recently said ‘High-resolution Raman spectroscopy still represents an as yet relatively untapped source of structural information’. The gas laser is potentially able to provide a sufficiently monochromatic source for Raman excitation to enable high-resolution Raman spectroscopy to be exploited to the full. Already the gas laser in its normally commercially available forms affords narrower line widths than the mercury arc (He-Ne, 6328 8, 0.04 cm.-l; Ar+ 5145 A 0.15 cm.-l) and very much narrower line-widths can be achieved with appropriate precautions albeit with a large drop in power. Despite this engaging prospect of virgin ground there appear to have been no publications dealing with laser-excited high-resolution Raman spectra of previously unstudied systems.Attention has so far been devoted to the prob-lems relating to sample illumination and scattered light collection and detec-tion. A recent series of papers traces the rapid progress in the solution of these problems. In 1965 Weber and port^^^ reported that they had obtained a good photographic record of the pure rotational Raman spectrum of methyl-acetylene at 0.5 atm. with an exposure time of 58 hr. using a cell (actual volume 340 ~ m . ~ ) with Brewster angle windows placed inside the cavity of a helium-neon laser of 20 mw output power. The volume of gas effective in producing scattering was only 0.59 ~ m . ~ compared with 3000 C M . ~ in a conventional mercury arc set-up but the exposure time was about 10 times longer.In 1967, Weber Porto Cheesman and Barrett78 showed that with a multipass Raman 76 B. P. Stoicheff ‘Advances in Spectroscopy,’ Interscience New York 1959 91. 77 A. Weber and S. P. S. Porto J . Opt. SOC. Amer. 1965 55 1033. 78 A. Weber S. P. S. Porto L. E. Cheesman and J. J. Barrett J Opt. SOC. Amer. 1967, 51 19. 92 D. A. Long cell inside the cavity of the helium-neon laser the photographic exposure time for rotational spectra were comparable with the classical mercury arc arrange-ment. They also made experimental tests of the effectiveness of various sample-illumination arrangements using a normal cell either inside or outside the cavity and found that the best arrangement was for the laser beam to be focussed into the cell inside the cavity. The illuminated volume effective in scattering is less than 10-7cm.3 in this arrangement and for a gas at normal pressure only 1011 molecules are involved.This optical arrangement the allied problems of collection of the scattered radiation and the superiority of pulse counting detection systems were fully discussed by Barrett and Adam~7~ in 1968. The two later papers present excellent pure rotational (02,N2,C02, CH3CzCH) and vibrational rotation spectra (02,N2 C02) directly recorded with the sample inside the cavity of an argon-ion laser with an intra-cavity power of 3-5 w at 4880 8 or 5145 A. Satisfactory pure rotation spectra using He-Ne 6328 A excitation (80 mw) and vibration-rotation spectra using Ar+ 4880 A excitation (1200 mw) can be recorded when the sample is placed outside the laser cavity at the focus of the laser beam and an additional con-cave mirror beyond the sample is adjusted to externally resonate the output laser beam through the sample.This sampling system is used on some commercially available Raman spectrometers with laser sources. Clearly then we can look forward to an expansion of activity in high-resolu-tion Raman spectroscopy. Although in the immediate future intensity con-siderations may restrict much of the work to excitation with the argon-ion laser where linewidths are only marginally less than that of the 4358 8 mercury line the need for only micro-samples and the partial removal of the restriction on colour open up interesting possibilities. The pure rotational Raman spectrumso of propyne and [2H4]propyne and the vibration-rotation Raman spectrums1 of [1,1 ,l-2H3]ethane have recently been investigated using con-ventional mercury-arc excitation.In high-resolution i.r. spectroscopy the current trend is the gradual refine-ment of an already well-established technique. Recent improvements in resolving power are leading to re-examination of the rotational and/or vibra-tion-rotation spectra of a number of relatively simple moIecuIes long familiar to those in this field. As a result new or improved values of many molecular constants are becoming available; the fine structure of bands can be more fully interpreted and better values of Coriolis coefficients may be obtained. A typical example is the recent study of the vibration-rotation bands of methylacetylene and [2Hl]methylacetylene by Thomas and Thompson.82 This has yielded values of aA and aB relating the rotational constants A and B in different vibrational states for a number of vibrations and all the Coriolis 79 J.J. Barrett and N. 1. Adams J . Opt. SOC. Amer. 1968 58 31 1. 8o S. I. Subbotin R. Kh. Safiullin V. I . Tyulin and V. M. Tatevskii Oprika i Spek-81 D. E. Shaw and H. L. Welsh Canad. J . Phys. 1967 45 3823. 82 R. K. Thomas and H. W. Thompson Spectrochim. Acta 1968,24 A 1337; R . K. Thomas and H. W. Thompson Spectrochim. Acta 1968 24 A 1353. troskopiya 1968 24 82 Part (ii) Infrared and Raman Spectroscopy 93 coefficients. Other molecules studied during the period under review include : C Z D ~ ~ ~ HF DF HCl and DCl,89 CH3F,So CH3Br,S1 CH3D,92 1°BF3 and 11BF3,93 13CH335C1 and 13CH337C1,94 trans-NzF~,~~ NF3,96 ~1H6]cyclopropane,97 HN3 HNCO HNCS and their deuterium derivative^,^^ allene,g9 and CH3C1.10° Griffiths and ThompsonlOl have considered the problems that arise in the analysis of the rotational spectra of symmetric-top molecules when the K structure is not resolved.Essentially the problem is that if resolution is in-complete and the K structure is not measurable the observed (average) posi-tions of the J lines will be determined by the intensity distribution within the K sub-structure of each J transition and this may vary significantly with J. It emerges that there are differences between prolate and oblate tops. For prolate tops @<A) the plot of v/(J + 1) us. (J + 1)2 will be linear with the intercept (2B - ~ D J K K ~ ) very close to 2B and the slope close to -405.With oblate tops the plot of v/(J + 1) us. (J+ 1)2 will lead to incorrect values of the rotational constants. The authors report new measurements on the rotational i.r. spectra of the prolate tops CD3F CD3Br and CDd CH3CN and CD3CN, and CH3CCH and CH3CCD. The values of B and DJ which they obtain are compared with microwave determinations and explanations are given of any differences. The rotational spectra of the oblate tops CHF3 and trimethyla-mine were also investigated. The microwave values of the rotational constants were used to calculate the apparent shift in the position of J lines due to unresolved K structure as a function of J. This shift increased from 0 to 0.20 cm.-l over the range J = 0 to J = 70.Only when this shift is corrected for 12C180,83 15N160 and 14N160,84 15N2180,85 12C16O2 and 13C1602,86 C2H2,87 83 C. Chackerian jun. and D. F. Eggers jun. J . Mol Spectroscopy 1968 27 59. 84 D. B. Keck and C. D. Hause J . Mol. Spectroscopy 1968,26 163. 85 J. L. Griggs jun. K. Narahari Rao L. H. Jones and R. M. Potter J . Mol. Spec-86 A. e Silva and M. Helena Ann. Phys. (Paris) 1967 2 217. 87 J. F. Scott J . Opt. SOC. Amer. 1968 58 142. 88 S. Ghersetti and K. Narahari Rao J . Mol. Spectroscopy 1968 28 27. 89 D. U. Webb and K. H. Rao J . Mol. Spectroscopy 1968,28 121 ; A. A. Mason and Alvin H. Nielsen J . Opt. SOC. Amer. 1967 57 1464; A. J. Perkins Spectrochim. Acta, 1968,24 A 285. R. Anttila and M. Huhanantti Canad. J . Phys. 1968 46 2025; W.E. Blass and T. H. Edwards J . Mol. Spectroscopy 1968 25 438. 9l R. Azria and C. Joffrin-Graffouillere Compt. rend. 1968 266 B 75. 92 C. Betrencourt-Stirnemann C. Alamichel and G. Graner Compt. rend. 1967, 93 C. W. Brown and J. Overend Canad. J . Phys. 1968,46 977. 94 J. L. Duncan and A. Allan J . Mol. Spectroscopy 1968 25 224. 95 S. Tung King and J. Overend Spectrochim. Acta 1967 23 A 2875. 96 G. W. Chantry H. A. Gebbie R. J. L. Popplewell and H. W. Thompson Proc. Roy. SOC. 1968 A 304 45; R. J. L. Popplewell F. N. Masri and H. W. Thompson, Spectrochim. Acta 1967 23 A 2797. troscopy 1968 25 34. 265 B 549; E. C. Leisegang and D. G. Parkyn J . S . African Chem. Inst. 1968 21 64. 97 J. L. Duncan J. Mol. Spectroscopy 1968 25 449. 98 B. Krakow R. C. Lord and G.0. Neely J . Mol. Spectroscopy 1968 27 148. 99 N. Van Thanh Ann. Phys. (Paris) 1967 2 241. loo M. Morillon-Chapey G. Graner and C. Alamichel Compt. rend. 1968 266 B, lol P. R. Griffiths and H. W. Thompson Spectrochim. Acts 1968 24 A 1325. 240 94 D. A . Long is a satisfactory linear plot of v/(J + 1) us. (J + 1)3 obtained which leads to the microwave values of Bo and DJ. In the case of trimethylamine an un-corrected plot leads to value of BO significantly lower than the microwave value. Inorganic Structural Studies.-The study of vibrational i.r. and Raman spectra to establish assignments of fundamental frequencies and to deduce symmetry or structure is well known and continues to be a major interest of chemical spectroscopists. The principles remain unchanged and the practice remains substantially the same apart from developments resulting from laser excitation of Raman spectra e.g.oriented single-crystal Raman spectroscopy which is discussed in another section. There seemed little point consequently in merely selecting at random a few examples since they would serve no more purpose than to illustrate already well-known principles. An attempt has therefore been made to present a reasonably complete survey of structural spectroscopic studies for smaller inorganic compounds ; most aspects of the extensive field of transition-metal complexes have had to be excluded on space considerations but complex halides have been treated fairly fully. 1.r. and Raman studies102 of XeOzF2 have been interpreted in terms of C2, symmetry with a molecule of pseudo-bipyramidal structure with the two fluorine atoms axial to the xenon and the two oxygen atoms with a lone pair in equatorial positions.The i.r. and Raman spectra of XeF6 have been studied.103 The i.r. spectrum shows more bond-stretching bands than would be expected for Oh symmetry. 1.r. studies of 104 alkali-metal aluminium hydrides MAlH4 (M = Li Na IS, Rb Cs) show that in solution A1H4 has a distorted tetrahedral structure and in the solid state the symmetry is lowered to C2,. A bridge structure is postu-lated. H H Force-constant calculations have been madelo5 for AU2C16 and it is found that the bridge bond stretching force constant is 73% of the terminal bond whereas in Al~Cl6 it is ca. 50%. The Raman and i.r. spectra of poly-crystalline TlAu(CN)2 suggestlo6 that while the Au(CN)2 grouping is linear, strong interaction with the T1 leads to an overall symmetry of C2,.Stammreichl07 has used Raman spectroscopy to determine the Hg-Hg lo2 H. H. Claassen E. L. Gasner H. Kim and J. Huston J . Chem. Phys. 1968,49,253. 1°3 H. Kim H. H. Claassen and E. Pearson Znorg. Chem. 1968,7 616; E. L. Gasner lo* T. G. Adiks V. V. Gavrilenko L. 1. Zakharkin and L. A. Ignateva Zhur. priklad. 105 D. M. Adams and R. G. Churchill J . Chem. SOC. (A) 1968 2141. 106 H. Stammreich B. M. Chadwick and S. G. Frankiss,J. Mol. Structure 1968,1 191. 107 H. Stammreich and R. Teixeira Sans J . Mol. Structure 1967 1 5 5 . and H. H. Claassen Inorg. ,Chem. 1967 6 1937. Spektroskopii 1967 6 806 Part (ii) Infrared and Raman Spectroscopy 95 stretching frequency in a series of mercury(1) salts and has discussed the varia-tions in relation to bond lengths.Raman spectra of mixtures of HgI2 with either molten HgC12 (220") or HgBrz (260") have been interpretedlo8 in terms of formation of mixed halides HgICl and HgIBr. Assignments have been made for yellow Hg212 yellow HgI2 and red HgIz from the Raman spectra of the s01ids.l~~ The far -i.r. spectra of these compounds and also HgC12 HgBr2, Hg(CN)2 HgO (red and black) and HgS (red and black) have been investi-gated.ll0 The formation of Hg(CN)I Hg(CN)312- and Hg(CN)21=- in aqueous solutions of NaCN and NaI to which Hg(II) has been added has been detected by Raman spectroscopy.lll The i.r. and Raman spectra of (H3N)zAgf and (H3N)2Hg2+ have been studied.l12 The metal-N skeletal vibrations give intense Raman scattering but the lines are very broad and only weakly polarised in aqueous solution; this is attributed to strong hydro-gen bonding between the ammine group and the solvent cage.Normal co-ordinate calculations were carried out for these ammines and for the isostructural dimethyl derivatives MezCd MezSn2+ MezHg MezTl+ and Me2Pb2+ and also for (F3C)zHg; variations in force constants are interpreted. 1.r. studies113 are in accord with a structure with twisted azide groups (CZ for Hg(N& and a symmetric trans-structure (C2h) for Hgz(N3)~. The i.r. and Raman spectra of Hg(CD3)2 have been reported for the first time for the liquid state.l14 Addison and coworkers115 have studied the i.r.and Raman spectra of solutions of zinc(II) cadmium(Ir) and mercury(I1) nitrates (and some halides) in acetonitrile. The nitrate spectra show strong perturbation of nitrate ions by solvated cations but only for Hg(I1) was a metal-oxygen frequency observed. In concentrated solutions of the zinc nitrate the principal zinc species is [Zn(MeCN)2][N03]2. 1.r. and Raman studies116 of aqueous solutions of Hg(N03)z and mixtures of Hg(NO&HzO and KN03 are con-sistent with the presence of Hg(N03)f and Hg(N03)~. 1.r. studies117 of various isotopic boroxines H3B303 in the gas phase support a non plan~(C3~) configuration rather than a planar model (D3h). Vibrational assignments have been made for some methyldiboranes.l18 The gas-phase i.r. spectra of MeBFz (and nitromethane) have been analysedllg in detail in terms of a theoretical model with free internal rotation.Cryoscopic and ebullioscopic evidence that Me2A.lF and EtzAlF exist as tetramers is supported by the i.r. 108 J. H. R. Clarke and C. Solomons J . Chem. Phys. 1968,48 528. log R. P. J. Cooney J. R. Hall and M. A. Hooper Austral. J. Chem. 1968 21 2145, ll1 J. Coleman R. A. Penneman L. H. Jones and I. K. Kressin Inorg. Chem. 1968,7, 112 M. G. Miles J. H. Paterson C. W. Hobbs M. J. Hopper J. Overend and R. S . 113 D. Seybold and K. Dehnicke 2. anorg. Chem. 1968 361 277. 114 J. L. Bribes and R. Gaufes Compt. rend. 1968 266 C 584. 115 C. C. Addison D. W. Amos and D. Sutton J . Chem. SOC. (A) 1968 2285. 116 A. R. Davis and D. E. Irish Znorg. Chem. 1968 7 1699. 117 F. A. Grimm L.Barton and R. F. Porter Inorg. Chem. 1968 7 1309. 118 J. H. Carpenter W. Jones R. W. Jotham and L. H. Long Chem. Comm. 1968,881. 119 W. J. Jones and N. Sheppard Proc. Roy. SOC. 1968 A 304 139. E. Decamps and A. Hadni J. Chim. p h j ~ . 1968 65 1030. 1174. Tobias Znorg. Chem. 1968 7 1721 96 D. A . Long and Raman spectra120 which also indicate that the AhF4 skeleton in these compounds is a planar 8-membered ring with D4h symmetry. The i.r. spec-trum121 of Ph3AI contains four AI-C frequencies and is consistent with a cen-trosymmetric dimeric structure. In an i.r. study1Z2 of Friedel-Crafts halides, heptane solutions e.g. of TiBr4-AIBr3 mixtures showed no detectable concen-tration of complexes such as TiBr3+ AIBr4- which have been assumed to be active catalysts of isobutene polymerisation.Raman studies123 of InCI2 suggest that in the molten state and probably also in the solid state the structure is In+InC14-. The i.r. spectra124 of benzene solutions of GaCl2 and GaBrz confirm the previously established ion-pair structure GaS(GaX4)- but the tetrahalogenogallate ion has symmetry lower than T d probably CzV. A speculative interpretation of the situation in benzene solution is that the gallium(1) ion has a co-ordination number of five being co-ordinated both to a benzene ring and to two of the chlorines in the anion. Beattie and co-w o r k e r ~ ~ ~ ~ have extended their earlier studies of Group 111 trihalides. The Raman and i.r. spectra of Akdh-6 AlzIs Ga2Br6 Ga2I6 and In& have been recorded in various phases and by extension of normal co-ordinate calcula-tions already developed for GazCIs complete assignments were made for all the compounds studied.Greenwood et aZ.,126 have investigated the i.r. and Raman spectra of the chloride bromide and iodide of indium(I1r). Their spectra support the bridged dimeric structure In216 with four-co-ordinate indium for the iodide by analogy with the spectra of GazBrs. The spectra of the chloride and bromide however indicate that in these two halides the indium is six-co-ordinate in a polymeric layer lattice. W a l t ~ n l ~ ~ has investi-gated the halides of thallium(rrr). A dimeric structure has been postulated for carbon suboxide polymer at room temperature from i.r. studies.12s 1.r. and Raman spectra129 support a CzV structure for the nitromethane anion in NaCH3NOz.An analysis of the group of bands in the Raman spectrum130 of liquid CC14 at ca. 775 cm.-l previously assigned to v3 and v1 + v4 shows that this group of bands arises almost entirely from difference bands and that the fundamental v3 although present is very weak. Silicon difluoride has recently been shown131 to be a relatively long-lived species (ca. 2 min.) and it has been possible to study the lZo J. Weidlein and V. Kreig J . Organonretallic Chem. 1968 11 9. lZ1 H. F. Shurvell Spectrochim. Acta 1967 23 A 2925. 192 P. Schmidt M. Chmelir M. Marek and B. Schneider Coll. Czech. Chem. Comin., lZ3 J. H. R. Clarke and R. E. Hester Chem. Comm. 1968 1042. 124 E. Kinseila J. Chadwick and J. Coward J . Chem. SOC. (A) 1968 969. 125 I.R. Beattie T. Gilson and G. A. Ozin J . Chem. SOC. (A) 1968 813. 126 N. N. Greenwood D. J. Prince and B. P. Straughan J . Chem. Soc. ( A ) 1968 1694. 127 R. A. Walton Inorg. Chem. 1968,7 640; ibid. p. 1927. 128 J. Wojtczak L. Weimann and J. M. Konarski Monntsh. 1968 99 501. 129 M. J. Brookes and N. Jonathan J . Chew?. SOC. (A) 1968 1529. 130 J. T. Kenney and F. X. Powell J. Chetn. Phys. 1967,47 3220. 131 V. M. Khanna R. Hauge R. F. Curl jun and J. L. Margrave J . Chetn. Phys. 1967, 1968,33 1604. 47 5031 Part (ii) Infiaved and Raman Spectroscopy 97 i.r. spectrum of the gas and determine two of the three fundamental frequen-cies (v1 and v3) for this molecule (symmetry CW). Combination of these frequencies with microwave data (v2 and centrifugal stretching constants) enabled a complete quadratic force field to be calculated.The relatively complicated i.r. spectra of gaseous silacyclobutane and [1 l-2H2]silacyclo-butane in the range 24-300 cm.-l have been analy~edl3~ in terms of a double minimum potential for the ring-puckering vibration. The potential barrier is calculated as 440 & 3 cm.-l and the dihedral angle of the puckered ring as 35-9 & 2" for silacyclobutane. Vibrational assignments133 have been made for the organogermanes CsHsGeBr3 and CsDsGeBrs. The far 4.r. spectra of a number of binuclear tin-metal compounds have been studied1Z4 to determine tin-metal frequencies. Whereas the Sn-Sn frequency is weak the tin-metal frequency in the heteronuclear tin-metal compounds is invariably reasonably strong.The vibrational spectra of zirconium tetrachloride indicate a poly-meric structure of ZrzCls units (symmetry D2h) and the spectra of Zr(N03)4 can be interpreted as for Sn(N03)4 and Ti(N03)4 with a zirconium co-ordina-tion number of 8 (symmetry D2d).135 An interesting Raman spectroscopic study136 of the chlorine isotopic structure of the totally symmetric Ti-Cl stretching frequency in Tic14 shows that it could not have originated from a simple tetrahedral molecule ( T d ) . An associated complex of lower symmetry (DM C2h or GV) with a chlorine-bridged dimer structure is suggested. Clark et aZ.13' have studied the MXs2-and MX4Yz2- ions (M = Ti Sn; X = Cl Br I). yield a band at ca. 1 . 5 ~ attributed to the solvated electron. Two Raman and i.r. studies139 of N2F4 agree in their conclusions that both trans(C2h)- and gauche(C2)-isomers are present at both ambient and lower temperatures and that both forms have similar energies.The i.r. spectrum of di-imide N2H2 has been analysed140 in terms of a planar trans-conformation. Provisional assign-ments have been made for the perchlorylimide anion (assumed GV) from i.r. studies141 of Kzf4NC103 and KPNC103 and for the anion HNClO3- (Cs symmetry) from i.r. spectra142 of KH14NC103 KH15NC103 KD14NC103, 1.r. reflection spectra of solutions of alkali metals in liquid 132 J. Laane and R. C. Lord J . Chem. Phys. 1968 48 1508. 133 J. R . Durig B. M. Gibson and C. W. Sink J. Mol. Structure 1968 2 I . 134 N. A. D. Carey and H. C. Clark Chem. Comm. 1967 292. 135 J . Weidlein U. Mueller and K.Dehnicke Spectrochim. Acta 1968 24 A 253. J. E. Griffiths J . Chem. Phys. 1968 49 642. 137 R. J. H. Clark L. Maresca and R. J. Puddephatt Znorg. Chenr. 1968 7 1603. 138 D. F. Burow and J. J. Lagowski J. Phys. Chem. 1968 72 169. 139 D. F. Koster and F. A. Miller Spectrochim. Acta 1968 24 A 1487; J. R. Durig I4O A. Trombetti Canad. J . Phys. 1968 46 1005. *41 A. I. Karelin Yu. Ya. Kharitonov and V. Ya. Rosolovskii Zhur. priklad. Spek-142 A. I. Karelin Yu. Ya. Kharitonov and V. Ya. Rosolovskii Zhur. priklad. Spek-and J. W. Clark J. Chem. Phys. 1968 48 3216. troskopii 1968 8 256. troskopii 1968 8 458 98 D. A. Long and KD15NC103. Goubeau et ~ 1 . ~ 4 ~ state that force-constant calculations144 for NC1032- suggest a double N-Cl bond and a single C1-0 bond.Force-constant calculations based on i.r. frequencies suggest that the geometry of N203 is not unequivocally known. The vibrational assignments for the hyponitrite ion have been revised as a result of further i.r. studies.145 The fundamental frequencies of NFClz have been assigned and c0rrelatedl4~ with those of the isoelectronic molecule CHFC12. Two groups of ~pectroscopists~~~ have intrepidly determined the Raman spectrum of NC13 and agree in finding four frequencies (two polarised) as expected for a pyramidal GV structure. Temperature-intensity i.r. studies14* of PF5 at - 85-25"c show that a band at 301 cm.-l previously assigned as a fundamental is a difference band. Raman and i.r. spectra149 of the solids PC15,SnCh and 2PC15,SnCh support the formulations [PCI4]+[SnC15]- and [PC14+]z[SnC162-] previously advanced on 31P n.m.r.evidence. The vibrational spectra150 of MePC14 suggest that in the solid the structure is MePC13'Cl- whereas in non-ionising solvents the compound is monomeric probably with CzV symmetry. 1.r. and Raman studies151 of polycrystalline PH41 and PDd yield assignments for internal and external modes and barrier heights for phosphonium ion re-orientation in the lattice. The vibrational spectra of solid diph~sphinel~~ are consistent with a trans-structure ( C Z ~ ) . Gas-phase i.r. studies153 of AsF5 confirm a triangular bipyramid structure. The i.r. and Raman spectra of solutions of AsC13 and AsBr3 in tributyl phosphate (TBP) have been interpreted154 in terms of formation of complexes AsC13,2TBP and AsBr3,2TBP.The Raman spectra155 of aqueous solutions containing [0H-]/[As1I1] in the range 3.5-15.0 give evidence for four species As(OH)3 AsO(OHz)- AsO~(OH)~- and AsO~~-. N.m.r. studies show AsC15,PC15 to have the ionic structure [PCh]+[AsCl6]-. The Raman spectrum156 of this compound contains a line attributable to PCl6- formed photochemically. The Raman spectra of solid SbCl5 indicates157 the existence of two forms. The spectrum of the low-temperature form is similar to that of 143 J. Coubeau E. Kilcioglu and E. Jacob Z . anorg. Chem. 1968 357 190. 144 W. A. Yeranos and M. J. Joncick Mol. Phys. 1967 13 263. 145 M. N. Hughes J . Inorg. Nuclear Chem. 1967 29 1376. 146 R. P. Hirschmann L. R. Anderson D. F. Harnish and W. B. Fox Spectrochim. 14' P. J. Hendra and J.R. Mackenzie Chem. Comm. 1968 13 760; M. Delhaye, 14* Sister R. M. Deiters and R. R. Holmes J . Chem. Phys. 1968 48 4796. 149 P. Reich and W. Wieker Z . Naturforsch. 1968 23 737. 150 I. R. Beattie K. Livingston and T. Gilson J . Chem. SOC. (A) 1968 1 . 151 J. R. Durig D. J. Antion and F. G. Baglin J . Chem. Phys. 1968,49 666. 152 S. G. Frankiss Inorg. Chem. 1968 7 1931. 153 S. Blanchard Commis. Energie Atom. (France) Rapport 1967 No. CEA-R 3195. 154 J. E. D. Davies and D. A. Long J . Chem. SOC. (A) 1968 1757. 155 T. M. Loehr and R. A. Plane Inorg. Chem. 1968,7 1708. 156 W. Wieker and A. R. Grimmer Z . Naturforsch. 1947 22 983. 157 K. Olie C. C. Smitskamp and H. Gerding Inorg. Nuclear Chem. Letters 1968 4, Acta 1968 24 A 1267. N. Durrieu-Mercier and M.Migeon Compt. rend. 1968 267 B 135. 129; I. Savatinova and M. Markov Zhur. priklad. Spektroskopii 1967 7 599 Part (ii) Infrared and Rnman Spectroscopy 99 SbC14f in SbC14F and indicates octahedral co-ordination with either a dimeric structure in which two octahedra have one common edge or an ionic structure [SbC14]+[SbCl~]-. The spectrum of the high-temperature form is very similar to that of liquid SbC15 and justifies the assumption that it is composed of trigonal bipyramidal molecules of SbC15. Nitrato-complexes of bismuth(Ir1) have been studied by Raman and i.r. spectroscopy.158 The spectra are con-sistent with a nitrate of CzV symmetry and bidentate co-ordination. Intensity measurements indicate the existence of stepwise complexes containing one to four nitrates per bismuth.A water molecule is also bound to the bismuth. The Raman spectra of liquid NbF5 and TaF5 show no evidence159 for polymerisa-tion. The i.r. spectra in the range 500-200 crn.-l of NbC15 NbBrs TaC15, TaBr5 and wc15 lead to interesting conclusions.160 The dimeric form is retained in solution for NbC15 and TaCl5 but whereas wc15 is a dimer as a solid it may dissolve as a monomer in nonpolar solvents. Some earlier assignments are questioned. The i.r. spectra of a number of compounds con-taining the cluster (Nb&l12)n+(n = 2,3,4) have also been studied.lS1 C2 Symmetry has been proposed for H2S2 and force constants calculated.lSZ The i.r. spectrum of thionitrosyl chloride163 shows that it has the structure NSCl (C,) and not SNCl. The i.r. and Raman spectra of SS have been investi-gatedlS4 and assignments made on the basis of the known puckered ring structure ( D 3 d ) .There have been several spectroscopic studieslS5 of the Group VI monohalides M2Xz (M = S,Se; X = C1,Br); assignments have been clarified and none of the results contradict the gauche structure of CZ sym-metry. Other sulphur compounds investigated include several trimethylsul-phonium and trimethylsulphoxium compounds166 and [(CF3)zCF]zSF2 and CF3SF3 ;IS7 vibrational assignments have been made. Spectroscopic studiesl68 confirm a regular octahedral structure (Oh) for gaseous UFS but in the solid a tetragonal D4h distortion is observed. In solution vibrational spectralS9 of Mo(CN)s4- and W(CN)s4- are consistent with a square Archimedian anti-prism structure of symmetry D4d but in the crystal the symmetry is lower ( D 2 d ) .Assignments have been made170 for WCb. 158 R. P. Oertel and R. A. Plane Inorg. Chem. 1968 7 1192. 159 H. Selig A. Reis and E. L. Gamer J . Inorg. Nuclear Chem. 1968 30 2087. 160 R. A. Walton and B. J. Brisdon Spectrochim. Acta 1967 23 A 2489. 162 Numan Zengin Comm. Fac. Sci. Univ. Ankara 1967 16 9. 163 A. Mueller G . Nagarajan 0. Glemser S. F. Cyvin and J. Wegener Spectrochim. Acta 1967 23 A 2683. 164 J. Berkowitz W. A. Chupka E. Bromels and R. Linn Belford J . Chem. Phys. 1967, 47 4320. 165 E. B. Bradley C . A. Frenzel and M. J. Mathur J . Chem. Phys. 1968 49 2344; P. F. Hendra and P. J. D. Park J . Chem. SOC. (A) 1968,908; E. B. Bradley M. J. Mathur, and C. A. Frenzel J. Chem.Phys. 1967 47 4325. 166 J. A. Creighton J. H. S. Green D. J. Harrison and S . M. Waller Spectrochim Acta 1967 23 A 2973. 167 K. Sathianandan and J. L. Margrave Indian J. Pure Appl. Phys. 1967 5 464. 168 R. Bougon Commis. Energie Atom. (France) Rapport 1967 No. 3235. 169 K. 0. Hartman and F. A. Miller Spectrochim. Acta 1968 24 A 669. 170 J. C. Evans and S. Y . S. Lo J. Mol. Spectroscopy 1968 26 147. R. A. Mackay and R. F. Schneider Inorg. Chem. 1968 7 455 1 00 D. A . Long The i.r. spectroscopy of HF vapour throws doubtlil on the existence of a trimer although higher polymers do contribute to the absorption. The first vibrational spectrum of a planar x2Y6 molecule has been r e p ~ r t e d l ~ ~ for dimeric ICh. Raman studies173 of IF7 and ReF7 in the vapour state confirm D5h symmetry for both species.The vibrational assignments of IF6f have been the subject of conflicting r e ~ 0 r t s . l ~ ~ 1.r. and Raman spectra of the solid CsIF6 indicate175 that IF6- does not have the symmetry Oh. The vibrational spectra of the complexes pyridine-bromine and pyridine-bromine chloride that whereas in nonpolar solvents they are predominently un-ionised, in polar media there exists the equilibria 2PyBrX + (Py2Br)+ + (BrX2)-X = Br or Cl). I-Ili7 and stretching frequencies in iodine and iodine bromide complexes with pyridine and related compounds have been studied by i.r. spectroscopy and the results interpreted in terms of strength of donor-acceptor interaction. Spectroscopic studies179 of the salts [R4NJf[BrHBr]-(R = Me Et Pr Bu or pentyl) in the solid and in various solvents show that the anion may be linear symmetric or linear unsymmetric depending on the environment.Vibrational assignments have been made180 for ICN. The i.r. spectrum of Br2O is in accordlsl with C2 symmetry. The Raman spectrum of the permanganates has been observed1g2 for the first time by use of helium-neon excitation. The vibrational spectra of solid per-rhenic acid183 is consistent with the structure HORe03 (C3,) but in aqueous solutions of 80 % concentra-tion complete dissociation to Re04- occurs. Complex halides have been much investigated and although space pro-hibits a fully comprehensive account they do merit reporting in some depth. 1.r. evidence suggests184 the existence of a flat symmetrical BaCli ion in BaC12-NaC1 systems.Raman studies have been made1s5 of MgCV- CdCI,, CdClF CdBr, and CdI The far 4.r. spectra of anions of general formula ZIIB~,C~~-~~- ZnBrnIn2- and ZnCln14-n2- have been recorded and inter-preted.186 The assignments for AlC1 have been ~1arified.l~~ A Raman study 171 D. F. Smith J . Chem. Phys. 1968 48 1429. 172 H. Stammreich and Y. Kawano Spectrochim. Acta 1968 24 A 899. 174 K. 0. Christe and W. Sawodny Inorg. Chem. 1968 7 1685; J. L. Hardwick and 175 K. 0. Christe J. P. Guertin and W. Sawodny Inorg. Chem. 1968 7 626. 176 S. G. W. Ginn I. Haque and J. L. Wood Spectrochim. Acta 1968 24 A 1531. li7 J. Yarwood and W. B. Person J. Amer. Chem. SOC. 1968,90 594. 178 Y. Yagi A. I. Popov and W. B. Person J . Phys. Chem. 1967 71 2439. lSo S. Hemple and E.R. Nixon J . Chem. Phys. 1967 47 4273. ls1 C. Campbell J. P. M. Jones and J. J. Turner Chem. Comm. 1968 888. lB2 P. J. Hendra Spectrochim. Acta 1968 24 A 125. H. H. Claassen E. L. Gasner and H. Selig J . Chem. Phys. 1968,49 1803. G. E. Leroi ibid. p. 1683. J. C. Evans and G. Y. S. Lo J . Phys. Chem. 1967 71 3942. K. I. Petrov V. A. Bardin and V. G. Kalyuzhnaya Doklady Akad. Nauk. S.S.S.R., la4 J. R. Chadwick P. J. Cranmer and H. C. Marsh J . Inorg. Nuclear Chem. 1967,29, lB5 J. E. D. Davies and D. A. Long J . Chern. SOC. (A) 1968 2054. lS6 G. B. Deacon J. H. S. Green and F. B. Taylor Austral. J . Chem. 1967 20 2069. Is7 D. E. H. Jones and J. L. Wood Spectrochim. Acta 1967 23 A 2695. 1968 178 1097. 1532 Part (ii) Infrared and Raman Spectroscopy 101 of molten cryolitelEE at 1030" suggests the existence of the equilibrium AlFs3- + AlF4- + 2F-.The Raman spectra of chloride melts indicate189 that in the system InC12-LiCl-KC1 Inch- and are present; in Inch-LiCl-KCl InCl.52- and -InCls2- are present ; and in BiC13-LiCl-KC1, BiC14- BiC1s2- and a little BiCls3- are present. Although (Bu2NH2)3BiCls and (BuNH3)2BiCl5 contain the expected complex anion (BuNH3)3SbCls does not contain SbCls3- but has the structure Raman intensity mea~urem.ents~~1 on aqueous solutions containing various ratios of chloride ion to bismuth reveal the existence not only of BiC14-, Dick2- and BiCk3- but also species containing three two and possibly one C1- per BPI; with bromide ions BiBrs3- and not BiBrs5- is the highest species formed.1.r. and Raman studies of complex halides of tin titanium, and tellurium indicate1g2 the trigonal bi-pyramidal structures for the ions SnC15- SnBrs- and TiC15- but a symmetry lower than square pyramidal for Tech-. For (Et4N)Te3C113 the probable structure is (Et4N+)(TeC13+)3(Cl-)4 whereas (Et4N)TizCh appears to contain the chlorine-bridged structure Ti9Clg-. The Raman spectra of the molten complexes SF4SbF5 SeF4SbF5, SeF4AsF5 and TeF4SbF5 indicatelg3 ionic formulations [SF3]+[SbF6]-, [SeF3]+[SbFs]- and [SeF3Ii-[AsF6]- for the first three; the situation is less clear for the fourth but plausible alternatives are ionisation into distorted ions TeF3+ and SbF6- or a fluorine-bridged structure. The Raman spectra of complex anions of formula MXs2- (M = Se Te; X = C1 Br r) have been recorded in the solid phase and in solution;194 evidence was found for SeBr5-in solutions of SeO2 in concentrated HBr.The vibrational spectra of the tetra-halogeno-complexes of MnII have been studied assignments made and force constants cal~ulated.1~5 The intensities of the Raman frequencies of PtCls-have been reinvestigated and previously reported anomalies discussed and ~1arified.l~~ Vibrational assignments based on On symmetry have been madelg7 for Ucls2- and ThC162- from Raman and i.r. spectra. Thallium halides and complex halides have been the subject of a number of studies.198 lS8 C. Solomons J. H. R. Clarke and J. O'm. Bockris J. Chem. Phys. 1968 49 445. lSg J. T. Kenney and F. X. Powell J . Phys. Chem. 1968 72 3094. Ig0 R. A. Walton Spectrochim.Acta. 1968 24 A 1527. 191 R. P. Oertel and R . A. Plane Inorg. Chem. 1967 6 1960. Ig2 J. A. Creighton and J. H. S. Green J . Chem. SOC. ( A ) 1968 808. 193 J. A. Evans and D. A. Long J . Chem. SOC. (A) 1968 1688. lg4 P. J. Hendra and Z. Jovic J . Chern. SOC. ( A ) 1968 600. I95 H. G. M. Edwards M. J. Ware and L. A. Woodward Chem. Comm. 1968 540. Ig6 D. W. James and M. J. Nolan Inorg. Nuclear Chem. Letters 1968 4 97. lg7 L. A. Woodward and M. J. Ware Spectrochim. Acta 1968 24 A 921. lg8 T. Barrowcliffe I. R. Beattie P. Day and K. Livingston J. Chem. SOC. (A) 1967, 1810; D. M. Adams and D. M. Morris J . Chem. Sac. (A) 1968 694; M. J. Taylor ibid., p. 1780; J. E. D. Davies and D. A. Long ibid. p. 2050 102 D. A. Long Matrix-isolated Species.-Vibrational spectroscopy of species containing only a few atoms has always been particularly satisfying in that such systems offer the best chance of detailed and unambiguous analysis.The matrix-isolation technique in which normally unstable species are preserved in matrices of noble gases or nitrogen at very low temperatures has opened up a rich field of new simple species for spectroscopic study. An appreciable number of new species has been identified and studied in the past year by use of this technique. Many of these species are of interest as likely reaction intermediates and they often pose interesting structural problems. So far only i.r. spectroscopy appears to have been used for study of matrix-trapped species but with the availability of laser sources Raman spectroscopy should soon be playing a complementary role.In reviewing this interesting field the reporter has chosen to illustrate the technique by giving some detail of one investigation and to summarise the results for a number of other systems. Noble and Pimentellgg have recently made an i.r. study of the products condensed out at 1 4 " ~ from hydrogen chloride-chlorine-argon mixtures (1 1 160) after passage through a glow discharge. Apart from bands attribxtable to known species (e.g. HCl CIS) and to impurities (nonreproducible intensity) two new i.r. bands were observed. Since the only atoms available in quantity are hydrogen and chlorine these bands must arise from a new species of general formula HnCI,. One of the bands appeared at 956 cm.-l with associated bands at 952 cm.-l and 949 cm.-l.The relative intensities of these three components, approximately 9 :6 1 were those expected for the vibration of two equivalent chlorine atoms of natural isotopic abundance. The simplest molecule con-sistent with this observation would be the symmetric structure ClHCl of symmetry Dmh. On deuteriation the band at 956 cm.-l shifts to 729 cm.-l. The second and stronger i.r. band occurred at 696 cin.-l and showed no chlorine-isotope structure but shifted to 464 cm.-l on deuteriation. The band at 696 cm.-l is assigned to the i.r.-active antisymmetric stretch v3 and the band at 956 cm.-l to v1 + vg. The observed chlorine-isotopic shifts are fully compatible with these assignments. The frequency shifts on deuteriation can only be calculated satisfactorily with a quadratic-quartic function with a high quartic content but this is physically reasonable and a similar instance has been reported for HF2-.These results lead to a value of 259 cm.-l for v1, the symmetric stretch which for Dcoh symmetry should be Raman-active only. A band at this frequency was definitely absent from the i.r. spectrum, further supporting the centrosymmetric structure. The i.r.-active bending mode v2 was not observed although it is expected to lie well above 200 cm.-l, the lower frequency limit of the i.r. spectrometer used but it would be expected to have low intensity. The HCl2 species could play a role in transient phenomena involving chlorine atoms such as in the H2-CI2 explosion and in the HCl chemical laser.The reaction between lithium atoms and methyl halides during condensa-Ig9 P. N. Noble and G . C. Pimentel J . Chem. Phys. 1968 49 3165 Part (ii) Infrared and Raman Spectroscopy 103 tion in solid argon at 1 5 " ~ produces the methyl radical which is shown to be planar (D3h); any equilibrium deviation from planarity in excess of 5" is excluded.200 CF2 is formed when carbon atoms produced by photolysis of cyanogen azide react with molecular fluorine in argon201 at 1 4 " ~ . The com-plete valence force field has been calculated from the observed frequencies for WF2 and WF2 for a nonlinear structure. Photolysis of the CF2 sample produces CF3 which has a GV structure with an estimated 13" deviation from planarity. NCN produced by the photolysis of CNmN3 isolated in an argon matrix at 1 4 " ~ reacts readily with F2 to give NFzCN.If both fluorine atoms and NCN are present in appreciable concentration a new species tentatively identified as the free radical FNCN is produced.202 The reaction of photo-lytically produced F atoms with FCN in argon or nitrogen matrices at 1 4 " ~ yields203 the free radical F2CN. Further fluorine atom attack on FzCN produces inter aha CFzNF and CF3NF2. Simultaneous condensation of beams of lithium atoms and CBr4 in argon gives204 the radical CBr3. A secondary reaction of lithium atoms with CBr3 yields CBr2. Similarly the matrix reaction of lithium atoms and CC14 givesz05 the radical CCh followed by CC12 and the matrix reaction of alkali-metal atoms and perbromochloro-methanes produces206 the trihalogenomethyl radical followed by the tri-halogenomethyl alkali-metal compound.Vacuum-u.v. p h o t o l y ~ i s ~ ~ ~ of SiHzCl2 and SiDzClz in an argon matrix at 1 4 " ~ produces SiC12. Photolysis of OClO in an argon matrix at 4 " ~ gives208 the radical C100. There is some evidence that a structural isomer of this radical also exists. The free radical NCO is producedzo9 by vacuum-u.v. photolysis of HNCO in matrices at 4"-14"~. The action of a microwave discharge on a mixture of a noble gas, chlorine and bromine followed by condensation at 2 0 " ~ produces210 a series of new chlorobromo-compounds for example BrBrClz. These are T-shaped molecules analogous to ClF3. Evidence has been found21l for Li2F2 dimers (possibly linear with Cmv symmetry) when the vapour from solid LiF is deposited in an argon matrix at liquid helium temperature.The spectra of HCN and DCN in argon nitrogen and carbon monoxide matrices show no evidence for rotation of the monomer; the dimer has a linear or near-linear HCN-HCN structure.212 Cyclic dimers of HC1 have been identified213 2oo L. Andrews and G. C. Pimentel J . Chem. Phys. 1967 47 3637. 201 D. E. Milligan and M. E. Jacox J. Chem. Phys. 1968 48 2265. 202 D. E. Milligan and M. E. Jacox J . Chem. Phys. 1968 48 481 1. 203 M. E. Jacox and D. E. Milligan J . Chem. Phys. 1968,48,4040. 204 L. Andrews and T. Granville Carver J . Chem. Phys. 1968 49 896. 205 L. Andrews J . Chem. Phys. 1968 48 979. 206 L. Andrews and T. G. Carver J . Phys. Chem. 1968 72 1743. 207 D. E. Milligan and M. E. Jacox J .Chem. Phys. 1968,49 1938. 208 A. Arkell and I. Schwager J . Amer. Chem. SOC. 1967 89 5999. 209 D. E. Milligan and M. E. Jacox J . Chem. Phys. 1967 47 5157. 210 L. Y. Nelson and G. C. Pimentel Inorg. Chem. 1968 7 1695. 211 S. Abramowitz N. Acquista and I. W. Levin J . Res. Nat. Bur. Stand. Sect. A , 212 C. M. King and E. R. Nixon J . Chem. Phys. 1968 48 1685. 213 B. Katz A. Ron and 0. Schnepp J . Chem. Phys. 1967 47 5303. 1968 72 487 104 D. A . Long in HCI-Xe matrices. The spectrum of the species formed when krypton and chlorine (100 :1) are passed through a microwave discharge and then con-densed at 2 0 " ~ is attributable214 to a normally symmetric Cl3 species per-turbed from Adsorbed Species.-The amount of published work in this field is similar to that in recent years; a substantial portion continues to come from Russian laboratories.Almost all of it deals with i.r. investigations of adsorbed species. The potentialities in this field of Raman spectroscopy particularly with laser sources indicated in the previous report appear scarcely to have been exploited. Only two publications involving Raman spectroscopy were noted. Hendra and Loader continuing earlier have reported a study of acetaldehyde216 adsorbed on silica gel and suggested that condensation of acetaldehyde was catalysed at the surface to produce a physically adsorbed cyclic product. Pershina and Raskin217 investigated the Raman spectra of a variety of substances adsorbed at the surface of microporous glass silica gel, and aluminosilica gel. Perhaps their most interesting observations were that the spectra of SbC13 SbBr3 and dichloroethane show frequency shifts and intensity changes on absorption very similar to those observed for the phase transition liquid- crystal.An extensive review of i.r. spectroscopy of adsorbed molecules which covers 1950-1967 has been published.218 Of papers published during 1968 the reviewer has selected for mention the following as revealing interesting structural information. Studies of the adsorption of formic acid on Vz05 showed219 the existence of three species HC02H HzO and HC02-. Since e.s.r. studies show the formation of V4+ on adsorption it is suggested that the HC02- ions are adsorbed on V4f ions. The adsorption of benzene on highly dehydroxylated Aerosil (surface OH concentrations 1-2 OH/100 A2) occurs at low coverages mainly on OH sites through a 1 :1 interaction involving the benzene x-elec-trons.220 Adsorption on dehydroxylated areas becomes important when a significant number of OH sites have been utilised.The NH2 radical has been identified as forming on the surface of iron dispersed in silica when exposed to ammonia or mixtures of hydrogen and nitrogen in the temperature range 20-500"~. The role of this intermediate in the synthesis of ammonia is dis-cussed.221 Studies of the chemisorption of HCN C2N2 and BrCN on silica-based transition metals (Ni Ir Rh Pt and 0s) showed that chemisorption to Cm by an asymmetric lattice cage. 214 L. Y. Nelson and G. C. Pimentel J . Chem. Phys. 1967 47 3671. 215 P. J. Hendra and E.J. Loader Nature 1967 216 789. 216 P. J. Hendra and E. J. Loader Nature 1968 217 637. 217 E. V. Pershina and Sh. Sh. Raskin Optika Spektroskopiya Aknd. Nnirk. S.S.S.R., 218 M. R. Basila Appl. Spectroscopic Rev. 1968 1 289. 219 M. Adachi T. Imanaka and S. Teranishi J . Chem. SOC. Japan 1968 89 446. 220 A. Zecchina C. Versino A. Apiano and G. Occhiena J . Phys. Chew. 1968 72, 221 T. Nakata and S. Matsushita J. Phys. Chem. 1968,72 458. Otdel Fiz.-Mat. Nauk 1967 3 328. 1471 Part (ii) Infrared and Raman Spectroscopy 105 predominates.222 It suggested that all three gases dissociate to give CN radicals which then give cyanides (M-CN) and cyanates and isocyanates (MOCN MNCO) formation of the latter involving a hydrolysis reaction with OH groups. 1.r. frequencies characteristic of Fe3+ +NO+ Fez+ +NO have been observedz23 for NO adsorbed on Fez03 gel.The richness of the i.r. spectrum of hydrogen (or deuterium) chemisorbed on polycrystalline rhodium substrates is attributedz24 to multiple crystallographic sites available on the polycrystalline substrate. Bands are assigned to hydrogen molecularly chemisorbed in a linear fashion and to H-H and Rh-H stretches in a Rh-H-H-Rh bridged structure. Polarised i.r. studies of thin urea (and thiourea) films several hundred angstroms thick on a steel surface that the c-axis of the urea crystal was parallel to the metal surface and the c-axis of the thiourea crystal nearly parallel; there was also evidence that the urea molecule is deformed from the planar structure. Absorption bands observed in the 17OO-2200 cm.-l region when strongly electronegative gases like oxygen and chlorine are absorbed in ZnO powder have been identified226 as vibrations of bonds between carbon and nitrogen impurity atoms and oxygen in the bulk of the ZnO.It is suggested that adsorption of electron-withdrawing gases brings about this bond formation which appears to be limited to a depletion layer of 10-30 A in depth. Force-constant Studies.-The calculation of force constants continues to to attract the interest of a considerable number of spectroscopists. Significant studies on small molecules continue to be made; e.g. the fundamental harmonic vibrational frequencies and centrifugal distortion data for 16014N35C1 ls015N35C1 18014N35C1 and 1s015N35C1 have been used to calculate227 a unique general quadratic force field; the observed vibra-tional frequencies and rotational constants Bv for six isotopic carbonyl sulphide molecules (135 pieces of information in all) have been usedz28 to calculate 19 potential constants up to the fourth order in OCS.For larger molecules unique quadratic fields cannot be computed but detailed studies of families of related molecules can lead to useful results. Schererzz9 has closely fitted 176 observed out-of-plane vibrational frequencies in a series of chlorinated benzenes with a 23-constant force field calculated ‘stereo’ views of the vibration and shown that his results can be used to predict the fre-quencies of similar vibrations in systems containing other types of substituents. O~erend~~O has continued his work on anharmonicity in polyatomic mole-222 W.Mueller-Litz and H. Hobert 2. phys. Cheno.(Leipzig) 1967 236 84. 223 L. M. Roev and A. V. Alekseev Elem. Fotoprotsessy Mol. Akad. Nauk S.S.S.R., 224 W. H. Smith H. C. Eckstrom and B. Faer J . Phys. Chem. 1968 72 369. 225 Wateru Suetaka Bull. Chem. SOC. Japan 1967 40 2077. 2z6 D. M. Smith and R. P. Eischens J . Phys. and Chem. Solids 1967 28 2135. 227 L. H. Jones R. R. Ryan and L. B. Asprey J . Chem. Phys. 1968 49 581. 228 Y. Morino and T. Nakagawa J . Mol. Spectroscopy 1968,26,496. 229 J. R. Scherer Spectrochitn. Acta 1968 24 A 747. 230 S. Reichman and J. Overend J . Chem. Phys. 1968 48 3095. 1966,346 106 D. A . Long cules; this factor has usually had to be neglected for lack of reliable informa-tion.It is interesting to note that calculations on the force field of Os04 s h o ~ ~ 3 ~ that experimental mean amplitudes of vibration determined with the methods presently available are mostly not accurate enough to use for the precise calculation of interaction force constants. However formulae for the calculation of mean amplitudes of vibration continue to appear. There also continues unabated a passion for converting vibrational fre-quencies into force constants whatever the approximations involved. It must be emphasised that such force constants usually constitute only one of many possible sets of numbers which when fed into some approximate potential energy formula reproduce a set of observed frequencies. Yet such force constants are all too frequently the subject of solemn interpretation.A crude type of calculation employing order of magnitude force constants which are transferred between related molecules has been found to help with assignments in inorganic molecules. that a computer programme automatically cures nonconvergence troubles in a force-constant refinement calculation intrigues this author and no doubt many others who have experienced this difficulty . The Stimulated Hyper and Inverse Raman Effects.-The very large electric field strength associated with the radiation produced by a giant pulse laser has led to the observation of novel spectroscopic phenomena. Woodbury and Ng233 discovered the stimulated Raman effect in 1962. In 1964 Jones and Stoicheff 234 reported observation of the inverse Raman effect (or Raman effect in absorption) and in 1965 Terhune and coworkers235 published the first hyper Raman spectra.None of these new forms of spectroscopy has received much attention from chemical spectroscopists and only the stimu-lated Raman effect has been the subject of any substantial amount of study. The substantial reviews of the stimulated Raman effect and related pheno-mena by Bloembergen and by Schuler have been referred to earlier; they obviate the need for discussion here. It seems worthwhile however to explain briefly the nature of the other two new effects and to indicate their potential for chemical studies. When a scattering medium is irradiated simultaneously with intense monochromatic light of frequency vo (as from a giant pulse laser) and with an intense continuum the molecules are stimulated to emit radiation at vo and at the same time to absorb radiation at vo + Vm or vo - Vm from the con-tinuum where Vm is the frequency associated with a transition between two energy states in the molecule.Absorption at vo + Vm is associated with promotion of the molecule to a higher energy level whereas absorption at The statement in an 231 A. Mueller B. Krebs and S. J. Cyvin Acta Chem. Scatid. 1967 21 2399. 232 L. Nemes and M. Kemenczy Acra Chim. Acad. Sci. Hung. 1967 53 359. 233 W. J. Woodbury and W. K. Ng Proc. Inst. Radio Eng. 1962 50 2367. 234 W. J. Jones and B. P. Stoicheff Phys. Rev. Letters 1964 13 657. 235 R. W. Terhune P. D. Maker and C. M. Savage Phys. Rev. Letters 1965 14 68 1 Part (ii) Infrared and Raman Spectroscopy 107 vo - Vm is associated with a transition to a lower energy level.The resulting induced absorption spectrum is in effect an inverse Raman spectrum. All the Raman-active transitions for the molecule should be observed in the inverse Raman effect unlike the stimulated Raman effect where only one or two characteristic frequencies are observed. Since a complete Raman spec-trum in absorption can in principle be produced in the duration of the giant pulse (ca. 30 x 10-9 sec.) the study of free radicals and short-lived species should be possible. This method of producing Raman spectra may also help to overcome the problems associated with fluorescence. This promising technique has hardly received attention. A key problem appears to be the production of the intense continuum.Vodar et ~ 1 . " ~ have experimented with a continuum produced by passing a giant pulse laser through a cell containing krypton at 10 atm. pressure and reported observation of several lines in the inverse Raman spectra of organic liquids like chloroform and benzene. Otherwise there have been no further publications in this field to date. The dipole pind induced in a molecule by an applied electric field E is given in general by the nonlinear relationship Pind = RE f &$E2 + iyE3 + . . . The scattered radiation known as the Raman effect has frequency depen-dence vo & vm and arises from the linear term in this series. The selection rules intensities and polarisation characteristics are determined by the pro-perties of the second-order polarisability tensor a.The term in E2 is only significant for very large fields. In such cases there will be additional scattered radiation determined by the properties of the third-order hyperpolarisability tensor p. This has a frequency dependence of the form 2v0 & vm and is referred to as the hyper Raman effect. The selection rules are quite different from those for the normal Raman effect. In particular fundamentals inactive in both the i.r. and Raman effects may be hyper Raman active. Examples are the torsional frequency (A,) in ethane ( D M ) and no less than six fre-quencies (2Blu + 2Bzu + 2Ezu) in benzene ( D 6 h ) . The selection rules have been considered in detail by Cyvin Rauch and D e c i ~ s . ~ ~ ~ The effect is very weak and the only experimental work recorded is that of Terhune and co-workers235 who reported hyper Raman spectra of water fused quartz CC14, and MeCN.The hyper Raman effect is a promising new method for the study of molecular vibrational states previously regarded as 'spectroscopically inaccessible' . General.-It has not been possible to allot any substantial space to some topics. However in what follows an attempt has been made to set recent work in some of these fields in perspective and to draw attention to novel developments. 236 S. Dumartin B. Oksengorn and B. Vodar Compt. rend. 1965 261 By 3767 4031 ; 237 S. J. Cyvin J. E. Rauch and J. C. Decius J. Chem. Phys. 1965 43 4083. S. Dumartin B. Oksengorn and B. Vodar J. Phys. (Paris) Colloq. 1967 28 1 108 D.A. Long There has been about the usual number of publications dealing with intensities in i.r. and Raman spectra and the calculation therefrom of bond dipoles and bond polarisabilities and their derivatives. Recent publications of the Minnesota school on COFZ COC12 and on liquid hexa-fluor~benzene~~~ and liquid methyl iodide are broadly representative of i.r. intensity studies which generally have proceeded along well-established lines. The work of Nagarajan and DurigZ4l on intensities in dicyanodiacetylene is illustrative of Raman intensity studies. The gas laser has made possible the direct and accurate measurement of absolute Raman intensities242 and there should be an expansion of interest in this field. One growth point might be the idhence of resonance effects on Raman intensities which are not explicable in terms of existing theories.The CNDO method has been ~ s e d ~ 4 ~ to calculate for a number of molecules dipole derivatives which are in good agreement with values obtained from i.r. intensity measurements. Raman spectroscopy of polymers has been slow to develop although the laser is such a good source for the study of such materials. Reports have been confined to polypropene fibres,244 polymethylene and hexa-gonal and orthorhombic p~lyoxymethylene.~~~ Environmental effects have formed the basis of many spectroscopic studies. Typical of investigations of the effect of high pressures is the work of the Toronto school on pressure-induced i.r. absorption in hydrogen.247 Studies of solvent effects have covered a very wide range of topics e.g.the induced absorption spectra of hydrogen dissolved in Group IV tetra-halides248 which provide evidence for rotational motion of the hydrogen in solution; the i.r. spectra of saturated solutions of HC1 in fused alkali-metal chlorides249 which show that rotation of the HCl is unhindered; the i.r. spectra of solutions of strong electrolytes in D2O which contain bands attributable to hindered rotation and hindered translation of the water molecules;250 the investigation by of Raman spectra of D2O in Hz0 which supports the two-state model of water structure. There have been several interesting general papers relating to Raman spectroscopy. Tang and A l b r e ~ h t ~ ~ ~ have developed a Ranian intensity 23t3 M. J. Hopper J. W.Russell and J. Overend J . Chem. Phys. 1968 48 3765. 239 T. Fuyiyama and B. Crawford jun. J. Phys. Chem. 1968 72 2174. 240 C. E. Favelukes A. A. Clifford and B. Crawford jun.,J. Phys. Cfieni. 1968,72,962. 241 G. Nagarajan and J. R. Durig Bull. SOC. roy. Sci. Lisge 1967 36 552. 242 J. G. Skinner and W. G. Nilsen J . Opt. SOC. Amer. 1968 58 I 1 3. 243 G. A. Segal and M. L. Klein J . Chem. Phys. 1967 47 4236. 2M P. J. Hendra and H. A. Willis Chem. and Znd. 1967,2146. 245 R. F. Schaufele and T. Shimanouchi J . Chem. Phys. 1967,47 3605. 246 G . Zerbi and P. J. Hendra J . Mol. Spectroscopy 1968 27 17. 247 H. L. Welsh Proc. 1st Tnternat. Conf. Spectroscopy Bombay 1967 2 340. 248 M. 0. Bulanin and M. G . Mel’nik Optika Spektroskopiya Akad. Naiik S.S.S.R., 249 L. M. Gurevich,V.N. Devyatkin and K. F. Zhitkov,Zhur.fiz. Khim. 1968,42,1701. 250 D. A. Draegert and D. Williams J. Chem. Phys. 1968,48 401. 251 G. E. Walrafen J . Cheni. Phys. 1968 48 244. 252 J. Tang and A. C. Albrecht J . Chem. Phys. 1968 49 1144. 1967 3 214 Part (ii) Infrared and Raman Spectroscopy 109 theory with the Kramers-Heisenberg dispersion theory as a basis. Theimer253 has discussed the Raman effect in a plasma. Raman scattering from atmos-pheric oxygen and nitrogen has been 0bserved~5~ with a pulsed nitrogen laser and used to measure concentrations as a function of range. Koningstein and co-workers255 have made a series of studies of the electronic Raman effect for rare-earth ions in various crystal environments. Some transitions are associated with an asymmetric scattering tensor. 253 0. Theimer Proc. 1st Internat. Conf. Spectroscopy Bombay 1967 2 516. 254 D. A. Leonard Nature 1967 216 142. 255 J. A. Koningstein and 0. S. Mortensen Nature 1968 217 445. 255 0. S. Mortensen and J. A. Koningstein J. Chem. Phys. 1968 48 3971; J. A. Koningstein and 0. S. Mortensen Phys. Rev. 1968,168 75; J. A. Koningstein and 0. S. Mortensen J. Opt. SOC. Amer. 1968 58 1208; J. A. Koningstein and 0. S. Mortensen, Chem. Phys. Letters 1968 1 693; J. A. Koningstein Phys. Rev. 1968 174 411