Effect of the internal field on vibrational band shapes and intensities in liquids

Abstract

An analysis is given of the effect of the frequency dependence of the internal field upon band shapes and intensities in Raman and infrared spectra of liquids. It is shown that band shape in the Raman case is independent of the form of an isotropic internal field, and therefore a reflection of molecular interaction alone, whereas both effects are operative in generating infrared band shapes. Numerical calculations of infrared band shapes in liquids are presented for the Lorentz and Buckingham internal field functions. It is concluded that the interpretation of infrared band shapes in terms of molecular interaction must ordinarily be accompanied by an explicit analysis of the dependence of the band shape upon the frequency-dependent internal field.