Journal of Chemical Physics, Vol.115, No.7, 3230-3240, 2001
Green's function calculation of electron spin polarization. V. Quasi-equilibrium and fast mixing approximations for micellar radical pairs
Simple analytical formulas are derived for the electron spin polarization (CIDEP) generated in neutral radicals pairs in micellar solutions at high magnetic fields. The formulas are applicable for a locally weak exchange interactions, which could be integrally strong, and are based on the general analytic expressions obtained in the preceeding article of this series. We introduce two approximation schemes, for slow and for fast singlet-triplet mixing. For practical purposes these two cover the complete range of mixing rates. The approximation for slow mixing is similar to the quasi-equilibrium approximation, but we have derived more accurate expressions and explicitly evaluated all quantities. For fast singlet-triplet mixing we suggest a new and highly accurate approximation, which replaces the micellar RP with an effective freely diffusing RP with a redefined value of the exchange interaction. The accuracy of the approximations is documented by a comparison with numerically exact results. A specific feature for micelles is that the polarization as a function af the singlet-triplet mixing rate (q) has two maxima, where the low field maximum can be as large as 1/2 of the maximun possible value even for very small values of the exchange interaction.