Abstract
Recent research of external magnetic field effects (MFE) on chemical reactions is reviewed. The triplet radical pair which is generated by photo reactions can not take place back electron transfer or recombination reaction by a spin parity rule, and only take place them via singlet state after intersystem crossing. The magnetic fields affect the intersystem crossing rate between triplet and singlet states of the radical pair, and the yield of reaction products will be affected by the magnetic field. Several mechanisms, (a) Δg mechanism, (b) HFC mechanism, and (c) spin relaxation mechanism, for the effects on photoreactions have been proposed. The roles of these mechanisms for chemical reactions are described.
