A Statistical/Collisional Approach to Rates of Bimolecular Reactions at Low Pressure

ABSTRACT: An expression for the rate constant of gas-phase bimolecular reactions at low pressure is derived in the framework of collisional theory. The key feature of the proposed model is the calculation of the energy-dependent rate constant in terms of the collisional cross section and the probability of reaction, expressed as the ratio of the volume in phase space that leads to product over the total volume. The contribution of the internal energy of the reacting fragments is taken into account, as well as the relative translational energy. The resulting formulation is able to account for both negative and positive temperature dependences of the rate constants of neutral and charged species. The dependence of temperature of the bimolecular rate constant is given both for reactions with and without potential energy barriers. The performance of the proposed model is tested against experimental rate constant for three well-studied reactions by fitting the parameters of the model to experimental data at various temperatures.