We report direct Monte Carlo simulations of a chemical reaction system with bimolecular and termolecular dissociation and recombination reactions of the type M ϩAB M ϩAϩB. The simulations are carried out at the molecular level using a simple flexible reaction model for termolecular reactions satisfying all the requirements of momentum and energy conservation, microscopic reversibility, and equilibrium. Energy transfer among reactants and products is included. The method is especially useful for

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... treating reaction systems with nonequilibrium distributions and coupled gas dynamic-reaction effects. For systems with thermally equilibrated reactants the observed behavior is identical to that predicted by conventional methods.