Kinetic Equations for Orientational and Shear Relaxation and Depolarized Light Scattering in Liquids

The application of Mori's theory of fluctuations to the calculation of depolarized light scattering spectra of liquids is described. Two sets of kinetic equations are derived. The first is capable of describing the shear wave doublet observed by Fabelinskii and co‐workers and Stegeman and Stoicheff and reduces to the theory of Leontovich when the antisymmetric part of the stress tensor is ignored. The second set describes the doublet as well as the broad background observed in several laboratories and reduces to the theory of Volterra in the limit where antisymmetric stress is ignored. The angular dependence of the spectrum predicted by the first set of equations is compared with the experimental results of Stegeman and Stoicheff for aniline and quinoline. Good agreement is obtained for quinoline at all angles and for aniline at all but the highest scattering angle at which doublet structure was observed. Our results indicate that the relaxation of the antisymmetric part of the stress tensor may be important for discussing viscoelastic relaxation in aniline.