Light Scattering by Orientational Fluctuations in Liquids

Abstract

Tensor‐algebra techniques are used to derive expressions similar to those of Pecora and Steele for light scattering by liquids of anisotropic molecues, in a more compact form. The correlation functions are cast into a form in which their geometrical meaning is made obvious and is more immediately applicable to liquid models. A generalization of the Kirkwood $g$ factor to second‐rank tensors is defined. The theory is applied to the depolarized Rayleigh wings. It is argued on the basis of intensity and half‐width measurements that the diffuse line, which appears in the spectrum of benzene and several benzene derivatives, originates from reorientation of single molecules. This conclusion fits into a broader scheme incorporating results of dielectric, NMR, and viscosity measurements. It is suggested to relate the background, together with the narrow hole in the middle of the depolarized spectrum, to couplings of orientational fluctuations with shear waves.