Nonequilibrium Effects in the Kinetics of Isomerization Reactions and in the Kinetics of Dissociation and Recombination of Diatomic Molecules

Abstract

A study was made of the time evolution of a system of diatomic molecules undergoing dissociation and recombination and of a system of molecules undergoing isomerization. The starting point in each case was a master equation. The particular aims of the study were to determine the conditions under which the time evolution is describable by the appropriate phenomenological equation [Eq. (1) or (2)] and also to determine whether or not the phenomenological equations can hold under far from equilibrium conditions with forward and reverse rate constants whose ratio is not the equilibrium constant. In the isomerization it was found that the appropriate phenomenological equation [Eq. (2)] always holds after a sufficiently long time. In dissociation—recombination there exist systems in which the appropriate phenomenological equation [Eq. (1)] never holds. Certain necessary conditions involving rate constants for the elementary processes and the atom concentration must be fulfilled in order for this equation to ever hold. In both dissociation—recombination and isomerization the ratio of forward and reverse rate constants is always equal to the equilibrium constant when the phenomenological equations hold.