Theory of collision-induced forbidden Raman transitions in gases. Application to SF6

Abstract

A recent measurement by Holzer and Ouillon of the symmetry‐forbidden Raman bands ν₃(F_1u) and ν₆(F_2u) of gaseous SF₆ reveals a pressure dependence of the scattering cross section, i.e., the scattering process involves pairs of colliding molecules. The conventional Raman selection rule which holds for the ordinary dipolar polarizability, is violated by higher‐multipolar (so called hyper‐)polarizabilities. A theory is developed which enumerates all significant single‐molecule and pair contributions to the scattering cross section involving various hyperpolarizability tensors. Numerical values of the latter quantities are determined by comparison with experiment. Analysis of forbidden Raman bands can thus be used as a source of information on higher‐multipolar optical response functions.