Molecular dynamics simulations of nonequilibrium rate constant in a model exothermic reaction

In this letter, we study the nonequilibrium effects which appear in a therm ally activated exothermic reaction A + A --> products using the molecular d ynamics for reactive hard spheres. We have found that the rate constant is reduced with respect to its equilibrium value and the relative decrease of rate constant is similar to that observed for a thermoneutral reaction with the same activation energy. It is demonstrated that a simple phenomenology , which assumes a Maxwellian distribution of the energetic states for the r eactant and for the system as a whole, gives a good estimation of the noneq uilibrium rate constant. (C) 2000 Elsevier Science B.V. All rights reserved .