MAGNETIC-FIELD EFFECTS ON THE RECOMBINATION KINETICS OF RADICAL PAIRS

The recombination kinetics of radical pairs able to react only via the singlet channel are calculated within the framework of the radical pa ir mechanism, treating nuclear spins semiclassically. The form of the decay, which is in general nonexponential, depends on the applied magn etic field strength and the rate of electron spin-lattice relaxation. Analytical expressions are derived for the limiting cases of zero and high field, with very slow or very fast relaxation. The theory is test ed and verified by measuring the decay of the secondary radical pair o f photosynthetic bacterial reaction centers at low temperatures.