The role of local fields and interparticle pair correlations in light scattering by dense fluids

Abstract

The ‘ generalized Einstein-Smoluchowski ’ theory for depolarized scattering from dense fluids composed of non-spherical molecules, which was presented in a recent article, is combined with a generalization of Yvon's dielectric theory to the case of non-spherical molecules to yield depolarized scattering intensities. The results may be discussed in terms of complete statistical-mechanical expressions for the ‘ effective polarizability anisotropy ’, γ, of a molecule in a dense fluid, which differs from the gas-phase polarizability anisotropy, Δα. The formal results for γ have been evaluated numerically for four thermodynamic states of a molecular-dynamics simulation of homonuclear diatomics performed by W. B. Streett ; the equilibrium dielectric constant, <ε>, has also been evaluated. We find that the ratio, (γ/Δα)², which appears in the scattering intensity, may be significantly less than unity ; this fact is essential to the understanding of experimental scattering data. The variation of scattering intensities with density and temperature is discussed, as is the direct importance of orientational pair correlations.