Influence of molecular nonrigidity on the infrared absorption and Raman scattering line shape in dense media

Abstract

Starting from the well‐known infrared absorption and Raman scattering line shape expressions, the two situations where a complete frequency degeneracy (unresolved isotropic Raman band) is or is not present (absorption band, anisotropic Raman band, and resolved isotropic Raman band) are examined. Thus the influence of the nonrigidity of the interacting molecules on the line shape is studied. The physical mechanisms responsible for the dependence of the profiles upon the internal molecular vibrations are carefully analyzed. An application to the spectra of a diatomic molecule trapped in a rare gas crystal is made and the vibrational broadening of HCl and CO embedded in Ar, Kr, and Xe crystal is calculated.