Microscopic study of inertial and viscoelastic effects in dipolar solvation dynamics

Abstract

In this article theoretical studies of equilibrium and dynamic solvation of a dipole in a dense dipolar solvent are presented. A microscopic expression of the solvation free energy is derived within a linear equilibrium theory of dipolar liquids. It is found that the transverse component of the solvent polarization cannot be neglected and that it makes a significant contribution to the free energy of dipolar solvation. We also present a detailed study of the dynamics of solvation of a solute dipole which includes the inertial and viscoelastic responses of the solvent and the main results are as follows. (i) The dynamics is found to be appreciably different from that of an ion because of the contribution of the transverse polar modes in the former. (ii) The size of the solute can have interesting effects. (iii) The short time inertial response of the solvent may give rise to an oscillatory decay. However, one needs to use a non-Markovian theory with the viscoelastic response of the liquid included to understand these effects and such a theory is presented here for the first time. (iv) In the overdamped and Markovian limit and in the absence of translational diffusion, the present theory gives results similar to the dynamic MSA model of Rips, Klafter, and Jortner and of Nichols and Calef.