Photolysis and nonequilibrium reaction kinetics

The rate constant of a bimolecular gas-phase chemical reaction is determined by the energy distribution of the reactants and the cross section for the reaction. Systems in which photolysis and other nonequilibrium processes occur may have energy distributions which differ significantly from the equilibrium distribution. Analytical solutions are derived for the rate constant as a function of temperature for certain systems in which nonequilibium processes occur. The analytical solutions are compared with the numerical solutions and the agreement is found to be excellent, confirming the validity of the approximations that were made. Chemical reactions are simulated with the Monte Carlo method and the results again confirm the validity of the analytical solutions. Under certain nonequilibrium conditions, it is shown that the complex expression for the rate constant as a function of temperature reduces to a simple form, which resembles the Arrhenius equation. In this special case, the dependence of the results on the shape of the reaction cross section is investigated.