ENERGY ACTIVATION OF ADIABATIC AND NONADIABATIC ELECTRON-TRANSFER

Low-level and two-level approaches to above-barrier reactions are used to establish the borders between adiabatic and nonadiabatic electron transfer to either stable or unstable products. The multiple curve-crossing probability is equal to unity in a narrow ''energy window,'' just above the barrier, and slowly decreases with energy over it. When the reactants are the Langevin oscillators and the energy dispersion per period is less than the-width of energy window, Mel'nikov's one-level theory is appropriate. Otherwise (at higher friction) it must be replaced by the two-level nonadiabatic theory of Burshtein and Zharikov. The transition from an energy diffusion regime to transition state theory (TST) or perturbation theory results occurs within the Langevin model at much,lower friction than within the ''strong collision model'' considered previously.