Concerted electron and proton transfer: Transition from nonadiabatic to adiabatic proton tunneling

Articles you may be interested in Quantum and dynamical effects of proton donor-acceptor vibrational motion in nonadiabatic proton-coupled electron transfer reactions Predictions of rate constants and estimates for tunneling splittings of concerted proton transfer in small cyclic water clusters Tunneling currents in long-distance electron transfer reactions. IV. Many-electron formulation. Nonorthogonal atomic basis sets and Mulliken population analysis Nonadiabatic dynamics for processes involving multiple avoided curve crossings: Double proton transfer and proton-coupled electron transfer reactions A concerted electron–proton transfer reaction is discussed, in which proton tunneling occurs simultaneously with electronic transition. It is assumed that the potential in which the proton moves is formed by two electronic states, which in the absence of their interaction would cross in the region between the two minima of the proton adiabatic potential. The proton tunneling between the two wells is, therefore, coupled to a switch between the two electronic states. The later occurs only when the proton is in the tunneling region under the barrier. A simple analytical expression for the tunneling matrix element T DA is derived, which is uniformly correct for small and large values of the electronic coupling. For small electronic coupling our expression coincides with that obtained in the nonadiabatic theory of proton-coupled electron transfer reactions. For large electronic coupling the expression is reduced to that obtained in the Born–Oppenheimer approximation. The transition from nonadiabatic to adiabatic tunneling is governed by the magnitude of the Landau–Zener parameter defined for the tunneling process. The obtained result is discussed in the context of the proton tunneling time.