Some Applications of Time-Dependent Rate Constant Theory to Radiation Chemistry

Abstract

It is well known that rate constants for diffusion-limited reactions decrease with time after the start of an experiment, an effect due to the time required to establish a diffusion gradient of each reactant around the other. It is pointed out that slow reactions between ions also exhibit a time dependence because a finite time is required to establish the Boltzmann distribution of each type of ion around the other. The latter effect appears as an increase of rate constant with time for reactions between ions of opposite charge and a decrease for ions of similar charge. These time dependent effects are applied to the picosecond pulse radiolysis results of Wolff et al. on electron formation and decay in acetone and acid solutions, and to some competition experiments of Czapski and Peled. Effects attributed by them to reactions of a precursor of the hydrated electron are shown to be similar to expected consequences of time-dependent phenomena of the hydrated electron itself.