MAGNETIC ISOTOPE EFFECTS ON THE DECAY KINETICS OF MICELLIZED TRIPLET KETYL PHENOXYL RADICAL PAIRS - ROLE OF HYPERFINE, EXCHANGE, AND DIPOLE DIPOLE INTERACTIONS

The geminate recombination kinetics of ketyl-Phenoxyl radical pairs (RP) produced by quenching of triplet benzophenone by 4-phenylphenol and in corresponding perdeuteriated system in micellar solutions of sodium octyl (SOS) or dodecyl sulfates (SDS) in D20 have been examined by using the laser flash technique under an external magnetic field up to 0.43 T. The recombination rate and magnetic isotope effect (MIE) in zero magnetic field increase as the micellar size is decreased. Application of a very small magnetic field (0.01 mT) results in the pronounced retardation of deuteriated RP geminate recombination and MIE enhancement in SDS while the corresponding magnetic field effects in SOS are small. Under a strong magnetic field MIE becomes negligible. The magnetic field dependences and attendant regularities are discussed in terms of a simple kinetic scheme, which includes the singlet-triplet transitions in the separated and contact states of RP. The relative contributions of hyperfine coupling, exchange, and dipole-dipole interactions as well as the spin-orbit coupling may be revealed by the comparison of MIE magnetic field dependences in micelles of different size.