Molecular dynamics of high pressure reactions in condensed

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Pressure is an important physical parameter that determines selectivity, direction, and rates of chemical reactions. The effects of pressure on chemical kinetics are well studied and a vast amount of experimental data has been collected over the last fifty years. However, although they are qualitatively understood, all these data are greatly underutilized because of the lack of an adequate theory that accounts quantitatively for high-pressure effects. Fortunately, the recent advancement of computer technology seems to provide a proper instrument for tackling this problem.    Reaction mechanisms are usually discussed in terms of properties of transient states (transition states), through which reactants transform into products. Traditionally, the experimentally measured effects of pressure on reaction rates are expressed in terms of so-called volumes of activation, which represent the difference in volumes of transition states and reactants. Since the volumes of reactants are readily available experimentally, the volumes of activation provide a direct measure of the transition state volumes and thus a unique glimpse at these transient species.    We propose a new method for calculating activation volumes. Within our approach, the volume of a microscopic reaction system is determined as an Archimedean displacement volume of the system in a solvent and is found as a difference between the volumes of the pure solvent (N particles) and the solvent containing the system (N+1 particles). Preliminary results indicate that the volumes can be calculated with high precision.