ON SUPEREXCHANGE ELECTRON-TRANSFER COUPLING FOR A 3-COMPONENT SYSTEM

The Zusman equation is applied to derive the effective matrix elements for superexchange and sequential electron transfer for a three-component system consisting of a donor, a distant acceptor, and a bridging intermediate. Analytical expressions can be derived for the special ''degenerate'' case of triple crossing where all three Marcus free-energy parabolas cross at the same point. For the nondegenerate case, where the direct vertical energy gap between the donor and the intermediate is large, one expects the same result as for second-order perturbation theory.