Aspects of vibrational band contours

Abstract

An infra-red study was made of the molecular complex of hexafluorobenzene (HFB) in benzene solutions. Interactions between HFB and benzene lead to a frequency shift and a broadening of the band arising from the out of plane C-F bending vibration It is deduced that the intermolecular interactions are short lived, stochastic, are not simple polar interactions, and that the resulting forces are directed perpendicular to the ring plane. The band contours of the vibrational Raman band of chlorine in benzene/tetrachloromethane solution mixtures have been studied. Band fitting analysis of the complexed chlorine band using two Lorentzians, each with their isotopic sub bands, produced good simulations of the observed spectra. The consistency of the relative intensities suggests that they arise from complexes of the samestoichiometry. It is concluded that chlorine forms a 1:2 complex with benzene, with an equilibrium constant K = .095 elm mol . Entropy imply that there is a large molecular ordering compatible with the idea of specific structure of the complex. The vibrational Raman band of liquid chlorine was studied to shifts of 130 cm from the band centre. The second moment of the anisotropic component is about 15 above the theoretical value. Good exponential decays of the second order orientational correlation function are observed from t> 0.2 ps. The resulting relaxation times are well reproduced by a microviscosity equation. The results are in reasonable accord with n.m.r. relaxation times. Absolute intensity measurements have been made on the fundamental vibrations of methyl iodide, by integrating the optical density over the absorption band. Exact band fitting of the theoretical spectra, to the experimental spectra was not possible, no explanation can be offered. The intensity measurements were analysed in terms of the dipole moment derivatives with respect to symmetry coordinates, using three formulations of the vibrational angular momentum correction. Gribov's formulation is considered superior to the earlier Crawford hypothetical isotope method. Barrow and Crawford also derived a formulation similar to Gribov's.