Extended Fokker-Planck model for molecular rotations in liquids

Extended Fokker-Planck (FP) equations are generalized stochastic equations which describe the evolution of a set of coordinates, loosely referred to as solute, coupled with a relevant set of solvent variables. The applicational range of multidimensional stochastic operators is wide. In this paper we focus attention on model ''liquid'' systems. We discuss the effect of various kinds of cage degrees of freedom on the relaxation of orientational and angular momentum correlation functions of a probe molecule, for a model liquid composed of planar rotating dipoles interacting via a cosine potential. The results of numerically exact and asymptotic solutions of FP equations are used to interpret the dynamic behaviour of polar liquids in the frequency regions of dielectric relaxation and far-infrared absorption.