Photochemical accumulation and recombination of ion pairs undergoing the singlet-triplet conversion

Real time resolved kinetics of photoinduced electron transfer in solution is investigated theoretically. The results confirm that within the unified theory of bimolecular photoionization followed by geminate recombination the slow diffusional tails in long time kinetics of charged products are unavoidable, if ion pairs constitute a one component system. We demonstrate that observed quasi-exponential asymptotics can only be due to the multi-component nature of the reaction products. For the reaction under consideration we expect these components to be ion pairs in singlet and tripler spin states. The reaction pathway of spin interconversion and subsequent recombination of ions to both ground and triplet states of neutral reactants is proposed, whose prediction can be directly checked experimentally. (C) 1998 Elsevier Science B.V. All rights reserved.