Instantaneous and permanent photoionization

The bimolecular ionization of photoexcited molecules is theoretically inves tigated assuming the light pumping of moderate intensity is either instanta neous or permanent. The kinetics of energy quenching and ion-radical accumu lation and recombination after delta -pulse excitation are studied beyond t he rate concept, in the framework of Integral Encounter Theory (IET). The r esults are compared with those obtained within extended Unified Theory (UT) , contact and Markovian approximations, and a widely accepted exponential m odel. When there is a shortage of accepters the theory becomes nonlinear an d discloses the striking effect of electron-transfer saturation. In such co nditions and under permanent illumination IET is the sole formalism appropr iate for a full time-scale (non-Markovian) description of system relaxation . The original program for solving nonlinear IET equations for particle con centrations was developed and first used to calculate the kinetics of relax ation to equilibrium and to a stationary regime. The non-Markovian correcti ons to the quantum yields of fluorescence and charge separation obtained nu merically are in good correspondence with analytic estimates of these quant ities.