Molecular dynamics simulation of a chemical reaction in solution

Abstract

We have carried out a study, using the molecular dynamics simulation technique, of a simple model describing a chemical reaction in solution. The model consists of a three body reaction complex, in which a light particle transfers between two heavier species, surrounded by a ‘bath’ of 106 spherical liquid particles. Within the reaction complex we employ a three body potential with an effective barrier to transfer which depends strongly upon the separation of the heavy particles. We study the behaviour of a correlation function related to the kinetic rate constant for the transfer reaction and examine the validity of the transition state approximation to this quantity. It is found that transition state theory improves as the mass of the transferred particle increases. Arrhenius plots yield an effective activation energy, although the transfer is not best described as a barrier hopping process. We also compute the predicted incoherent neutron scattering spectrum due to light particle motion and compare with a recent study of proton transfer in the system trifluoracetic acid/water using this experimental technique. It is found that the transfer contributes to the quasielastic line in the predicted spectrum and also produces a broad, low intensity, feature extending into the inelastic region. Both effects would be expected to be difficult to observe experimentally.