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Infrared and Raman spectra in the gas phase are reported for trimethoxyborane, B(OCH 3 ) 3 , and its 13 C 3 and d 9 isotopomers. Some liquid phase Raman data were also obtained. Quantum-chemical (QC) studies of structure and force field have been made with B3LYP and MP2 models. These studies highlight the change in configuration of the methyl groups with change in basis set, within the C 3 h point group. Scaled QC force fields together with the new spectra enable assignments of fundamental bands to be improved. A Fermi resonance involving ν 12 is examined. The difference in strength between the two types of C–H bond in each methyl group is reckoned to be rather less than that deduced earlier from IR spectra of B(OCHD 2 ) 3 . This conclusion is supported by QC data for dimethylether. MP2 estimates of certain interaction force constants are superior to those from B3LYP calculations. Abnormal scale factors for the torsional motion involving the O–B–O–C system identify deficiencies in the QC models employed.

Raman spectra of the gaseous phase of SnCl 2 are reported over the temperature range 666 K to 1047 K. The development of a furnace designed for optical studies at temperatures up to 1100 K is described. Agreement with previous Raman studies is excellent and in addition new features are observed which are attributed to the dimeric species Sn 2 Cl 4 . Extensive force constant calculations have been carried out to establish the structure of this molecule. The results show that the dimer molecule has C s -symmetry with one bridging chlorine atom. The enthalpy of formation of Sn 2 Cl 4 has been calculated using second-law methods, and is in agreement with a previous result from mass spectrometry. Predicted vibrational band wavenumbers from force constant calculations are used to calculate values of the heat capacity C p ⦵ , the enthalpy H T ⦵ - H 298 ⦵ , and the entropy S T ⦵ - S 0 ⦵ of Sn 2 Cl 4 from 0 K to 6000 K. The molten phase of SnCl 2 has also been examined.

The vapour-phase Raman spectrum of an alkali is reported. Bands attributable to sodium iodide monomers (240 cm−1) and dimers (204 and 224 cm−1) are present at 1084 K. The intensity ratios of the bands reflect the relative abundance of the species in the vapour phase at this temperature. Normal coordinate analysis was carried out to determine the position of the low-frequency Raman-active band. The results are compared with those of previous calculations. Values for the heat capacity,Cp0, enthalpy,HT0-H2980, and entropy,ST0-S00, of gaseous Na2I2 have been calculated by the methods of statistical mechanics.

The intensity of the ν(NO) stretching band of NO+2 at Δ ν = 1400 cm−1 in the Raman spectra of nitric acid—water—sulphuric acid mixtures has been studied to determine nitronium ion concentrations over the temperature range 293–313 K. The nitronium ion concentration in these mixtures was found to decrease with increase in temperature. The nitrating species for acid mixtures used in mono- and di-nitrations is consistent with nitronium ion, NO+2, but at a typical acid concentration of less than H2SO4:HNO3:H2O = 30:15:55 mole % used in industrial mononitrations, there is no spectroscopic evidence for the presence of NO+2. It is suggested that the nitrating species in these weaker acid solutions is he acid hydrate, H2NO+3, which is a weaker nitrating species than NO+2.

Infrared and Raman spectra have been obtained in the gas phase for the species M( 12 CH 3 ) 2 , M( 13 CH 3 ) 2 , M( 12 CD 3 ) 2 and M( 13 CD 3 ) 2 , where M  Zn, Cd and Hg. All but one of the skeletal bending modes are observed directly in the infrared. 13 C frequency shifts confirm the assignment of a number of combination and overtone bands, including the 1300 cm −1 bands of Zn(CH 3 ) 2 and Cd(CH 3 ) 2 which arise from ν 10 + ν 14 . Infrared spectra in the 1400–1500 cm −1 region are difficult to interpret but the evidence points to both the δ as CH 3 modes lying near 1445 cm −1 . A number of Fermi resonances affecting δ s CD 3 levels are identified in the d 6 species. Some features of the ν as CH 3 bands can be explained in terms of existing free internal rotor theory. Observed values of 13 C frequency shifts are generally in good agreement with those from previous scaled ab initio calculations. There is an urgent need for high resolution studies of jet-cooled samples.

Raman spectroscopic studies of silicon (IV) fluoride and tetraethylammonium chloride in chloroform and nitromethane solutions confirm the existence of the hitherto unreported chlorotetrafluorosilicate (IV) ion, SiF 4 Cl − . The observed vibrational wavenumbers for this new species are compared with those calculated using an SVFF approximation based on the SiF 2− 6 and SiCl 4 species, and with the isoelectronic molecule PF 4 Cl.

The intensities of the bands in the Δν = 450 to 500 cm−1 region of liquid boron(III) chloride, characteristic of v(BCl) stretching as a function of temperature in the range 234–287 K are used to determine the average enthalpy of boron—chloride bond formation for the dimer species, (BCl3)2. Intensity measurements show that liquid boron(III) chloride contains 2% and 11% of dimer species at 287 K and 234 K, respectively, and the average ΔH° = −0.52 ± 0.08 kJ mol−. Extrapolation indicates that liquid boron(III) chloride will contain about 20% dimer molecules near its freezing point at 166 K. The ΔH° value for dimer formation is discussed in terms of the molecular interaction.

Vapour-phase Raman spectra of NbCl5 at temperatures between 418 and 580 K and of 1:1, 1:2 and 2:1 mixtures of NbCl5 and SnCl2 at temperatures between 359 and 676 K have been recorded. Several features have been observed in spectra from the mixtures which do not correspond to those known for the pure components and these vibrational bands have been assigned to the vapour-phase complex NbSnCl7. Normal coordinate analysis has been carried out for the proposed structure of the complex. Complexation of the tow components is shown to enhance the volatility of NbCl5 by a factor of 3.75 at 420 K. SnCl2 is shown to be more volatile when complexed with NbCl5 than in its pure phase. Predicted vibrational band wavenumbers from force constant calculations, combined with observed wavenumbers have been used to calculate values for the heat capacity, C°p, the enthalpy, H°T–H°298, and the entropy, S°T–S°O, of NbSnCl7(g) from 0 to 6000 K.

Force constants for an SVFF approximation have been calculated for the molecules Ni[P(CH3)3]4, Pt[P(CH3)3]4 and P(CH3)3 using an FG matrix method and vibrational assignments with the assumption of methyl point masses. The observed wavenumbers of the M[P(CH3)3]4 species were fitted using six primary and eight interaction force constants. The vibrational assignments for the Ni[P(CH3)4]4 and Pt[P(CH3)3]4 species are confirmed by the force constant calculations. Comparisons are made with the force constants for the related molecules Ni(PF3)4, Pt(PF3)4 and Ni(PCl3)4. The metal—phosphorus stretching force constant in Pt(PF3)4 is 3.5 times larger than the corresponding value in Ni(PMe3)4. Changes in the force constants are discussed in terms of the metal—phosphorus—methyl bonding in the M[P(CH3)3]4 species.

SVL fluorescence spectra of styrene-β-D2 (STYD2) are assigned and enable many new assignments to be made in the absorption spectrum. In turn these allow the determination of the first four levels of the C(1)-C(α) torsional vibration ν″42 in the ground electronic state. Using new information regarding the geometry of the molecule, in particular that 〉C(1)C(α)C(β) is about 130°, together with torsional vibrational levels from the electronic absorption spectrum and the Raman spectrum, has enabled us to determine the ν42″ torsional potential function V(φ) for styrene (STY) and STYD2: STY V(φ)/ cm −1 = [1070(1 − cos 2φ) − 275(1 − cos 4φ) + 7(1 − cos 6φ)] 2 ; STYD 2 V(φ)/ cm −1 = [1070(1 − cos 2φ) − 270(1 − cos 4φ) + 4.5(1 − cos 6φ)] 2 . This potential function changes appreciably when one quantum of ν″29, a substituent in-plane bending vibration, is excited. There is a very strong Duschinsky effect affecting ν42 and ν41, a substituent out-of-plane bending vibration, and intensity measurements in the SVL spectra have enabled us to obtain Duschinsky coefficients corresponding to the changes of normal coordinates from the X to the A state.

The Raman spectra in the region 250–1000 cm−1 are reported for six orientations of a single crystal of K2SeO4 over the temperature range 293–87 K. In the spectra of the paraelectric phase at 293 K, splitting of the internal vibrations of the SeO ion is in accord with the predictions of group theory. No significant differences are found in this internal frequency region in the ferroelectric phase at 87K. It is concluded that only minor lattice distortions are occurring at the ferroelectric phase transition which may be associated with a soft mode in the 22 cm−1 region.

The Raman spectra in the region 400–4000 cm−1 of single crystals of NaNH4SO4·2H2O in various orientations are reported for the temperature range 293–87K. NaNH4SO4·2H2O undergoes a transition at 101 K from a paraelectric phase to a ferroelectric phase. The changes in the Raman spectra of the constituent species, NH, SO and H2O as the temperature is lowered indicate that below the phase transition there are non-equivalent ions in the unit cell. The abruptness of the spectral changes at 101 K suggests a large lattice distortion in accord with the predictions of magnetic resonance studies.

Infrared and Raman spectra are described and assignments are reported for CH 3 CDCl 2 and CD 3 CHCl 2 , together with new i.r. data for CH 3 CHCl 2 and CD 2 HCHCl 2 . Using previously obtained “isolated” CH stretching frequencies, the above data enable the trans and gauche stretch—stretch interaction force constants to be determined: f ′ g = ±0.011, f ′ t = ∓0.026 mdyn/A. Similar values, f ′ g = +0.016, f ′ t = −0.029, may be obtained from the earlier spectra of CHD 2 CHD 2 due to Van Riet. The relations between the fundamental deformation bands and their overtones and combinations are examined in order to estimate the accuracy of predictions of v s (= v 3 ) for the CH 3 and CD 3 groups from the 4 × 4 refinement and frequency sum rule. The data can be interpreted so as to give good agreement on the values of v O s of 2920 cm −1 (CH 3 ) and 2115 cm −1 (CD 3 ), provided that there are significance resonance shifts on both 2δ a and 2δ′ s levels. That this is the case seems to be true for the CD 3 group, but is uncertain for the CH 3 one.

The [I2CN]− ion, previously only known in aqueous solution, has been isolated as its caesium salt; and the previously unknown [BrICN]− ions [ClICN]− have been isolated as their caesium salts. The Raman and IR vibrational spectra of these three caesium salts have been investigated in detail and indicate that the halide ions coordinate to the I atom of ICN to form linear (C∞ν) [X—I—CN]− ions (X=I, Br or Cl), contained in a centrosymmetric unit cell. This C∞ν structure is supported by a normal coordinate analysis for the [IICN]− ion.

Improved room temperature Raman spectra obtained from oriented single crystals of K2SeO4 of high quality are reported and discussed. The new results show that some of the earlier spectra contained spurious bands and that some genuine bands were incorrectly assigned.

Crystals of semicarbazide hydrochloride, NH2CONHNH+3Cl– are paraelectric above 294 K and ferroelectric below. The Raman spectra in the region 0–1800 cm–1 of oriented single crystals of semicarbazide hydrochloride and its perdeutero analogue have been recorded over the temperature range 298–87 K. In addition the infrared spectrum of semicarbazide hydrochloride in a KBr disc at 298 K has been recorded in the range 250–1700 cm–1. The Raman spectra have been analysed in relation to the structural changes occurring with the change of phase. The spectroscopic results support the X-ray evidence that the transition to the ferroelectric phase is second order and involves no major structural change. Comparison of the infrared and Raman spectra suggest that LO–TO splitting is unimportant.

Crystals of semicarbazide hydrochloride, NH2CONHNH+3Cl– are paraelectric above 294 K and ferroelectric below. The Raman spectra in the region 0–1800 cm–1 of oriented single crystals of semicarbazide hydrochloride and its perdeutero analogue have been recorded over the temperature range 298–87 K. In addition the infrared spectrum of semicarbazide hydrochloride in a KBr disc at 298 K has been recorded in the range 250–1700 cm–1. The Raman spectra have been analysed in relation to the structural changes occurring with the change of phase. The spectroscopic results support the X-ray evidence that the transition to the ferroelectric phase is second order and involves no major structural change. Comparison of the infrared and Raman spectra suggest that LO–TO splitting is unimportant.