THE MAGNETIC-FIELD INFLUENCE ON BRIDGE-ASSISTED ELECTRON-TRANSFER

The influence of an external magnetic field on the rate of electron tr ansfer is studied theoretically for the case of a donor-acceptor compl ex with paramagnetic ions as bridging sites. We demonstrate for a brid ge with a single and with two paramagnetic ions that the applied magne tic field causes a blocking effect of the electron transfer. Each para magnetic ion staying in its electronic ground state is assumed to redu ce its spin from S to S-1/2 if the transferred electron is coupled to it. Such a spin reduction determines the magnetic field dependence of the transfer rate in a specific manner. The magnetic field dependence is derived at low temperatures in utilizing the Wigner 6j-symbols meth od. For the case of two paramagnetic ions per bridge the exchange inte raction between them has been additionally included into the calculati ons. It is responsible for the step-like dependence of the rate consta nt on the magnetic field, as well as for the creation of a rather narr ow field-strength region where the rate constant drops to zero. (C) 19 97 Elsevier Science B.V.