Independent pairs modeling of the kinetics following the photoionization of liquid water

An analytic treatment for the short-time recombination following the photolysis of water is presented. The technique is used to look at the way that the spatial distribution of the reactants resulting from the photoionization influences the escape probability and the time-dependent decay kinetics of the solvated electron. The predictions of the analytic method are compared with the experimentally observed decay of the solvated electron. Two different distributions are used to describe the initial separation of the hydrated electron from the hydroxyl radical and the hydrated proton with which it may react. To match model to experiment requires either a Gaussian of standard deviation 0.6 nm or an exponential with a characteristic width of 0.3 nm. The two distributions have the same root-mean-square separation, 1.0 nm, once the initial overlap of reactants is taken into account.