Spin-correlated radical pairs in micellar systems: Mechanism of CIDEP and the micelle size dependence

A new model of time-resolved EPR in micellized radical pairs is introduced. The model is based on numerical integration of the master Liouville equation for spin-correlated (micellized) pairs and free (escaped) radicals. The diffusion of radicals is considered in terms of a supercage model. This approach is used to analyze data on laser flash photolysis of C-13-carbonyl labelled ketone alpha-deoxybenzoin in aqueous sodium alkyl(10-12) sulphate solutions. EPR lines of C-13-benzoyl radicals exhibit antiphase structure (APS) typical of spin-correlated pairs. Due to very large APS splitting, 0.8-1.5 mT, the ST0 polarized lines from free benzoyl radicals can be isolated spectrally. The observed line shape of the APS cannot be accounted for in the standard model of effective exchange potential. The shape of the APS is shown to be controlled by spin exchange relaxation in micellized pairs.