Molecular theory of solvation and solvation dynamics in a binary dipolar liquid

Abstract

Both the equilibrium and the dynamical aspects of solvation of a classical ion in a dense binary dipolar liquid are investigated by using a molecular theory. The theory properly includes the differing inter- and intramolecular correlations that are present in a binary mixture. As a result, the theory can explain several important aspects of the nonideality of equilibrium solvation energy (broadly known as preferential solvation) observed in experiments. We find that the nonideality of solvation depends strongly on both the molecular size and the magnitude of the dipole moment of the solvent molecules. The interactions among the solvent molecules play an important role in determining the extent of this nonideality. The dynamical calculations are based on a generalized Smoluchowski equation which has been used extensively for studies in one component liquid. For binary liquid, our study reveals rich and diverse behavior such as dependencies on the sizes, the transport coefficients and the polar properties of the components. The theory offers a detailed picture of the dependence of the solvation dynamics on the composition of the mixture. It is predicted that the dynamics of solvation in a binary liquid is, in general, nonexponential and that the details of the dynamics can be quite different from those in a one component liquid. In particular, the continuum model is found to be grossly inaccurate in describing the solvation dynamics in binary mixtures and rather extreme conditions are needed to recover the predictions of the continuum model which can be attributed to the nonideality of the solvation. The predicted results are used to study the dynamic solvent effects on the rate of an adiabatic electron transfer reaction in a binary liquid. The theoretical predictions are also compared with the available experimental results.