Heuristic model of ST0 chemically induced electron spin polarization (CIDEP) and its time evolution

CIDEP due to ST0 mixing in radical pairs is treated by breaking the mechanism down into its sequential steps: (1) singlet-triplet mixing; (2) polarization in a weak spin exchange encounter; (3) possible depolarization by strong spin exchange. (4) Repetition of this sequence until polarization or permanent pair separation occurs. Basic diffusion theory determines the probabilities and durations of these steps, thereby averaging over the high frequency fluctuations of the exchange interaction that complicate other treatment but which are irrelevant on the long time scales of the polarization process. The model yields the polarization as a function of time after formation of the pair, and the final polarization agrees well with the results of Stochastic-Liouville treatments.