Diffusion-controlled reactions. I. Molecular dynamics simulation of a noncontinuum model

Abstract

The molecular dynamics simulation method is extended to study a model of diffusion-controlled reactions. This allows a molecular description of solvent at an equal footing of reactants. Nondiffusional dynamic behavior of reactive molecules is found at short times. It enhances the rate of reactive encounter in comparison to the prediction of Smoluchowski theory. The model studied in this work can be regarded as a theoretical prototype of fluorescence quenching. In this context it is shown that the nondiffusional dynamics is mainly responsible for the discrepancy between Stern–Volmer plots measured in a continuous excitation experiment or obtained by integrating the time resolved fluorescence intensity. The other aspects such as the long-time behavior of survival probability, solvent effect as well as competing effect from finite concentration of one reactive species are also studied in some detail.