Magnetic field dependent yield of geminate radical pair recombination in micelles. Effect of intraradical spin lattice relaxation

The combined effect of coherent spin evolution and spin lattice relaxation on the magnetic field dependent yield of radical pair (RP) recombination in micelles is analyzed quantitatively using the exponential model (EM) and its supercage extension. Furthermore we show that the much simpler Johnson-Merrifield approximation agrees with the EM when the coherent transition frequencies are larger than the rate of escape from the micelle; but for nearly degenerate states only the EM is applicable. Relaxation induced by anisotropic hyperfine- and g-tensors is investigated. For large values of the anisotropic interactions and for long residence times of the RP in the micelle (i.e. small escape rates) the effect is substantial. The most pronounced effect is the decrease of the escape yield Y(B) caused by the Delta g-relaxation at high fields (B > 1 T). Some hitherto unobserved spikes in the Y(B) curve are found at high fields. These are due to accidental degeneracies of the high field states.