MAGNETIC-FIELD EFFECT ON THE PHOTOOXIDATION EFFICIENCY OF FERROCENE

The cage escape efficiency eta(ce) Of radicals ill the electron transf er quenching of triplet methylene blue by ferrocene in acetonitrile wa s found to be sensitive towards an external magnetic field. The field dependence of the effect corresponding to a monotonic decrease of eta( ce) was determined in a field range from 0.0 to 3.2 T, where it reache s a value of -20.7%. The effect is analyzed in terms of a spin chemica l model wherein the effective rate of geminate reverse electron transf er, regenerating the singlet ground state of the reactants, becomes ma gnetic field dependent due to magnetic mixing of non-uniformly reactiv e spin sublevels by the anisotropic Zeeman interaction. From the analy sis, the absolute values of the Mtr constants of spin-allowed reverse elect-roll transfer (605 ns(-1)), cage escape (15 ns(-1)), and electro n spin relaxation in the ferricenium cation (154 ns(-1)) could be dete rmined.