Brownian dynamics simulation of a chemical reaction in solution

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Abstract
We present a study, using the brownian dynamics simulation technique, of a simple model of a chemical reaction in solution. The model consists of the transfer of a particle between two substrate species in a reaction complex which interacts with its surroundings through frictional effects and random force terms. We pay particular attention to the regime in which both the barrier to transfer and the degree of interaction between the transferred particle and its environment are low. Correlation functions associated with the kinetic rate constant are investigated, and the dependence upon temperature, barrier height, mass and coupling coefficient are studied. Even at low barrier height it is possible to define the rate constant and to obtain near-Arrhenius behaviour. The classical isotope effect is found to hold in the high mass limit. The transition state approximation is investigated and the approach to the diffusion controlled limit is observed as the mass and coupling increase. Comparison is also made with various low coupling, single particle, theories, none of which is found to apply to the model in hand.