SPIN CORRELATION AND MAGNETIC-FIELD EFFECTS IN RADIOLYSIS

When pairs of radicals meet at random the reaction probability is limi ted to one quarter by spin considerations, unless spin relaxation is e xceptionally fast. Conversely, dissociation or ionisation from a singl et state can always be followed by geminate recombination, providing t he initial spin correlation is retained. The spin correlation must dec ay eventually because of spin relaxation but usually a faster process intervenes - spin evolution due to hyperfine coupling. This gives rise to magnetic field effects: so too does electronic fine structure (zer o-field splitting) in processes involving pairs of triplet excited sta tes. The role of these processes in radiation chemistry is reviewed an d the possible future applications of magnetic studies are discussed. (C) 1997 Elsevier Science Ltd.