Theory of the Dissociation Kinetics of Diatomic Molecules

Abstract

A general rate constant for the reaction of diatomic molecules is presented. The derivation directly includes nonequilibrium and non‐steady‐state [W. G. Valance and E. W. Schlag, J. Chem. Phys. 45, 216 (1966)] effects, unless these are explicitly excluded, which can be done readily. Collisional transition probabilities of any general form can be employed in the evaluation of the final rate constant. The specific case of a nearest‐neighbor model (one‐quantum transitions) is also investigated, since this leads to some great simplifications in the final rate constant. An upper and a lower bound to this rate constant are derived, and are shown to be usually extremely close to one another. The exact solution for this case is given in terms of an iteration of the lower‐bound solution. A value can be computed for the upper‐bound solution which lies above that computable from any specific transition probability model, and is independent of such models. In using this maximum value for a nearest‐neighbor rate constant it is shown that this value usually lies below the experimental values, hence indicating an inherent inadequacy in the nearest‐neighbor model for at least these reactions. These results are also compared with those from simple‐collisional theory and a non‐nearest‐neighbor model.