Nonequilibrium computer simulation of a salt solution

Abstract

A nonequilibrium computer simulation is performed to investigate the relaxation of a realistic polar solvent near a rapidly dissociating ion pair. The time evolution of the reaction coordinate, the ultrashort time scale changes in solvation energy and solvent forces, the local density response, the heating of certain librational degrees of freedom, and the time-dependent polarization are studied during the first 125 fs of the reaction. It is found that the relaxation behaviors in the anionic and cationic shells are very different. On average, the solvation process under study takes about 30-40 fs to break the original cage. After another 50 fs, the solvated ion pair reforms a new metastable structure, which feeds energy back into the reacting system to break the cage further. This procedure is apparently repeated many times until dissociation is complete. The results obtained in this work provide a graphic picture of some of the features of ultrashort dynamics of ionic photodissociation reactions in a polar medium.