Theory of magnetic field effects on radical pair recombination in micelles

Abstract

Magnetic field effects (MPE) of radical pair (RP) recombination in micelles are investigated both analytically and numerically. The confinement effect of a micelle is modeled by a spherically symmetric potential well. The results show that the contribution from ST_ transitions to all kind of MFEs is significantly increased due to the confinement effect. The spin exchange relaxation is also increased causing the STo-contribution to CIDEP to be essentially reduced. Surprisingly a pronounced effect of ST+ transitions on CIDEP is found when the confinement is strong. Simple analytical expressions for the recombination probability and for CIDNP and CIDEP are rigorously derived and a high accuracy is found by comparison with the numerical results. The results are interpreted in terms of a simple supercage model which is based on the assumption that the process can be separated into two stages: (1) a fast initial geminate stage in which the radicals are thermalised within the micelle and (2) a slower decay of a quasi-equilibrium state by escape from the micelle.