Blocking of bridge-mediated electron transfer by an external magnetic field

The rate expression for the low-temperature bridge-mediated electron transfer (ET) in a donor–acceptor complex is derived including the influence of an externally applied magnetic field. A blocking of the ET is demonstrated for a bridge with two paramagnetic ions having incompletely filled 3d-shells. The blocking can appear (i) if each of the paramagnetic ions has a “frozen” angular momentum in its ground-state multiplet, and (ii) if the ion (which has to stay in its electronic ground-state) reduces its spin from S to S−1/2 during the formation of the virtual bound state with the transferred electron. To observe the blocking the spin projection of the transferred electron has to be m=−1/2, and the spin projection of each paramagnetic ion should be its minimal value M=−S.