BLOCKING OF BRIDGE-MEDIATED ELECTRON-TRANSFER BY AN EXTERNAL MAGNETIC-FIELD

The rate expression for the low-temperature bridge-mediated electron t ransfer (ET) in a donor-acceptor complex is derived including the infl uence of an externally applied magnetic field. A blocking of the ET is demonstrated for a bridge with two paramagnetic ions having incomplet ely filled 3d-shells. The blocking can appear (i) if each of the param agnetic ions has a ''frozen'' angular momentum in its ground-state mul tiplet, and (ii) if the ion (which has to stay in its electronic groun d-state) reduces its spin from S to S - 1/2 during the formation of th e virtual bound state with the transferred electron. To observe the bl ocking the spin projection of the transferred electron has to be m = - 1/2, and the spin projection of each paramagnetic ion should be its mi nimal value M = -S. (C) 1998 Elsevier Science B.V. All rights reserved .