Unimolecular Reactions

Abstract

Unimolecular reactions are those involving a change in only one molecular of ionic structure. Dissociation or isomerization of the molecule may be considered as characteristic examples of such reactions. Defining unimolecular reactions in such a way, we disregard the question about the kinetics describing appropriate processes. It appears that the kinetics of these reactions (or the reaction order) depend on the extent to which perturbations, caused by the chemical process as such, affect the internal distribution function of the reactants. Two familiar limiting cases — first-order and second-order — correspond to a very small or very large perturbation of the Boltzmann distribution function. The fact that under certain conditions the chemical reaction rate is completely controlled by the restoration rate of the perturbed (with respect to equilibrium) distribution function, i.e. by the relaxation rate, allows to consider from the same standpoint the dissociation of diatomic and polyatomic molecules and also the reverse processes of atomic and radical recombination.