THEORETICAL ASPECTS OF CHEMICALLY-INDUCED MAGNETIC-POLARIZATION

The role of theory in guiding and simplifying interpretation of electron spin resonance experiments on photochemical and other reactions involving free radical intermediates is surveyed. Emphasis is on models which provide a physical picture as well as quantitative estimates for such phenomena as the radical pair mechanism of chemically induced electron spin polarization (CIDEP), the closely related process of spin exchange during radical-radical encounters, and spin lattice relaxation. Some specific topics discussed are: 1) an improved quantitative model of ST0 CIDEP combining an initial stage of polarization development followed partial loss of this polarization to spin exchange, 2) the relation between the spin exchange and recombination rate constants, and 3) simplification of spin-lattice relaxation in the common case of spin-rotation relaxation. The modification of the polarization processes in two-dimensional and closed three-dimensional systems is also discussed.