Cubic M4+P2O7 pyrophosphates of Ti, Zr, Hf, Sn, and Pb have been examined by X-ray powder diffractometry and by infrared, Raman, and Mössbauer 119Sn spectroscopy. The tin compound appeared to be of Chaunac's type I (with P2O7 groups oriented at random) and could be converted to type II (with ordered P2O7 groups) by heating to high temperatures. All the other preparations were of Chaunac's type II. Evidence from lattice parameters and intensity features of the Raman spectra suggests that the cubic MP2O7 pyrophosphates fall in two groups, one containing the compounds of the typical elements (Ge, Sn, Pb) and the other, the compounds of the transition elements. No support has been found for the view that the P—O—P groupings of the pyrophosphate anion in these compounds are linear. The 119Sn chemical shift in SnP2O7 is only slightly less negative than the shift in CuSnF6.4H2O, which makes SnP2O7 one of the most ionic compounds of tetravalent tin known. The observed quadrupole splitting in the Mössbauer spectrum of SnP2O7 arises largely from the contribution of the valence term to the electric field gradient at the Sn atom.

In the infrared spectrum of gaseous ethylene oxide the A1 C—H stretching and CH2 wagging modes are assigned at 3018 and 1148 cm−1, respectively. The previous assignment of the B1 ring deformation mode at about 890 cm−1 is not consistent with the spectrum, but its correct assignment is not clear. The infrared spectrum of ethylene oxide liquid and the frequencies of the fundamental modes in the gas and liquid states are presented.

This paper reports three independent studies. In the first study, the infrared band shapes and relative intensities of gaseous thiirane-d4 (ethylene sulfide-d4, C2D4S), the Raman spectrum of liquid thiirane-d4, and infrared spectra of gaseous cis- and trans-1, 2-dideuteriothiirane, (CHD)2S, are reported for the first time. The vibrational spectra of C2H4S, C2D4S, and some bands of cis-(CHD)2S are assigned from the symmetry analysis, group frequencies, infrared band shapes, and Raman polarization data. The frequencies so assigned are used to derive a modified valence force field, (MVFF), which reproduces them well, allows the remaining fundamental frequencies of cis-(CHD)2S to be found, and allows the spectrum of trans-(CHD)2S to be assigned. The MVFF is then further refined to optimize the fit to the 46 assigned frequencies of the four molecules. Twenty four nonzero force constants fit the 46 frequencies with an average error of 0.4%. The assignment is thus well based and self-consistent. In the second study, ab initio SCF calculations of optimum geometry, vibrational frequencies, and IR intensities of thiirane, thiirene, and a number of isotopically substituted derivatives are reported for the 6-31G*, 3-21G, and STO 3G bases. The force constants of thiirane from the 6-31G* basis are in good agreement with those of the MVFF when allowance is made for the fact that some were constrained to zero in the MVFF. The potential energy distributions from the ab initio and normal coordinate calculations agree well, with the former confirming some defects in the latter. The 6-31G* force constants multiplied by 0.80 reproduced the 46 observed frequencies with an average error of 1.4%. For thiirene and isotopic derivatives, the 6-31G* IR spectra are in much better agreement with experiment than previous results with smaller bases. In particular, significantly higher frequency C–S stretches are predicted with the 6-31G* basis. Nevertheless, a few discrepancies remain between experiment and the 6-31G* SCF results. In the third study, vibrational frequencies and IR intensities of thiirene and isotopic derivatives were evaluated at the CISD level of theory using a standard DZP basis set. In the DZP-CISD thiirene spectrum, the B1 C–H out-of-plane bend and its position relative to the A1 C–S stretch differ significantly from the 6-31G* SCF results, giving confirmation of the experimental assignments. However, the same DZP-CISD force constants predict that two low-frequency bands of thiirene-d1 are assigned incorrectly. No other significant discrepancies between theory and experiment remain for the thiirene species.

The infrared spectra of characterized samples of ethylene oxide hydrate made from 100% H 2 0 , 99.7% D 2 0 , and several dilute isotopic solutions, are presented between 4000 and 360 cm-I. The similarity between the absorption by the watcr ~nolecules in the hydrate and in ice I is discussed. The frequency and halfwidth of tlie O H and O D stretching modes of isolated HDO molecules in tlie hydrate are related to those in the disordered ice phases; the frequencies correlate rather well with the weighted-mean hydrogen bond lengths in these phases.The ethylene oxide vibrations show sharp, single-line absorption. The only exceptions are the ringbreathing mode which appears as a doi~blet, separated by 2 cni-', with m~~c h weaker absorption about 13 cm-' away on either side, and the ring deformation modes which interact with the vK(H20) niodes. The possible causes of this behavior are disci~ssed, but no firm conclusions can be drawn. The sharpness of tlie absorption by enclathrated ctliylene oxide, compared to that by liquid ethylene oxide, is brietly discussed in the light of modern theories of bandshapes in liquids. dans l'hydrate ont ete reliees a celles des phases dCsordonnCes de la glace ; la correlation dcs frtqi~ences est plut8t bonne avec la nioyenne pondCrCe dcs liaisons hydrogcne dans ces phases. Les vibrations de

The infrared absorption and Raman spectra of polycrystalline tetrachlorocuprate(II) dihydrates M2CuCl4.2H2O (M = K, Rb, Cs, NH4) contain minima in the OH stretching region which sharpen at low temperature. These minima are shown to be 'Evans holes', or negative absorption features, caused by Fermi resonance between the broad and intense H2O stretching fundamental V1 and a relatively narrow band due to the overtone of the H2O bending vibration 2V2. Our findings confirm that Fermi resonance can lead to unusual spectral features, which must be taken into account in the analysis of the stretching region of the spectra of H2O and D2O in condensed phases, as has been done by Scherer etal. for the spectrum of liquid water.