Nonlinear, Nonpolar Solvation Dynamics in Water: The Roles of Electrostriction and Solvent Translation in the Breakdown of Linear Response

Abstract

The fact that the motion of solvent molecules defines the reaction coordinate for electron-transfer and other chemical reactions has generated great interest in solvation dynamics, the study of how the solvent responds to changes in a solute's electronic state. In the limit of linear response (LR), when the perturbation caused by the solute is “small”, the relaxation of the excited solute's energy gap should behave identically to the relaxation dynamics of the unperturbed solute following a natural fluctuation of the gap away from equilibrium. Despite the fact that the addition of a fundamental unit of charge to a small solute results in a solvation energy that is tens or hundreds of kT, computer simulations of solvation dynamics have found, with only a few exceptions, that LR is obeyed for changes in solute charge. Essentially none of this work, however, accounts for the fact that the solutes in real chemical reactions undergo changes in size and shape as well as in charge distribution. In this paper, we...