Resonance effects on superexchange and sequential electron-transfer reactions due to energy-level crossing Original Research Article

A treatment using the Zusman equation is presented for electron-transfer reactions at high temperature involving three Marcus parabolic potential surfaces. Using the nonperturbative Zusman approach, analytical expressions are derived for the superexchange and the sequential electron-transfer rate constants, covering three regimes for the direct vertical energy gap ΔE: the nondegenerate, the degenerate and the quasi-degenerate regimes. For a small ΔE both superexchange and sequential mechanisms can be competing, and the rate constant can deviate significantly from the classical Marcus description which only considers the lowest-order perturbation theory. The novel resonance effects on these two processes due to degenerate energy-level crossing are examined.