Theory of depolarized light scattering

Abstract

We have studied the VH depolarized light scattering spectrum of liquid triphenylphosphite over a wide range of temperature. At high temperature and low viscosity the Rytov doublet corresponding to shear-orientational modes is observed, while at low temperature and high viscosity weak side peaks corresponding to viscoelastic shear waves are seen. The fluctuations of the dielectric tensor ? which give rise to depolarized light scattering have been adequately described over the whole temperature range by a ’’three-variable’’ generalized hydrodynamic theory. In contrast with virtually all previous studies of VH spectra we use the independently measured shear viscosity as a known, rather than adjustable, parameter. As a result of our analysis we can express ?(t) as a linear combination of the molecular reorientation density ?(t) and the microscopic stress tensor ?(t), and we find that the intermolecular scattering represented by ?(t) is important at high as well as low temperature. We are also able to evaluate the autocorrelation function of ?(t) in the low-wave number, long-time limit as the sum of two exponential decays with comparable amplitudes. We include a comparative study of other theories.