Comment on the mechanism of proton-coupled electron transfer reactions

Abstract

We present detailed studies of the mechanism of proton-coupled electron transfer (PCET) reactions based on the recently proposed one-dimensional model system by Fang and Hammes-Schiffer [J. Chem. Phys. 106 (1997) 8442]. Three different mechanisms: a concerted ET–PT mechanism, a sequential PT→ET mechanism, and a sequential ET→PT mechanism, have been suggested. We have examined the dynamical coupling between the proton and electron degrees of freedom, which is responsible for subtle differences in various PCET reaction mechanisms. For the concerted ET–PT and the sequential ET→PT mechanisms, the dynamics of the quantum wavepackets for the combined proton–electron system are consistent with proposed mechanisms. In contrast, for the sequential PT→ET mechanism, it is found that the electron transfer (ET) apparently happens prior to the proton transfer (PT) for the conditions adopted in the present calculations. The different dynamical behavior of the PT→ET and ET→PT mechanisms is partially attributed to the time-scale differences arising from the mass disparity of the proton and electron.