Molecular-dynamics studies of annihilation reactions

The validity of the reaction-diffusion formulation of annihilation kinetics, with randomly distributed initial conditions, is investigated by molecular-dynamics simulations of dense hard-disk fluids. For the reaction A + B → C + C quantitative agreement is found. Yet, this proves not to be the case for the reaction A + A → C + C, where major discrepancies are observed. For this latter reaction, more sophisticated theories predict a logarithmic decay law of the form ln (t)/t. The microscopic simulations essentially confirm this prediction.