A theory for the rate constant of a dissociative proton-coupled electron-transfer reaction

A theory that predicts the rate of a dissociative proton-coupled electron-transfer reaction is presented. The electron and proton transfer is treated as one quantum event that is driven by the coupling of the respective charges to the solvent's orientational polarization. The final state, where both electron and proton have transferred, corresponds to a repulsive surface for the proton motion. Consequently, the reaction products include a dissociated proton-transferred species. The origin of the repulsive surface is attributed to a combination of the hydrogen bond's relative weakness and the role of the solvent's electronic polarization in aiding the dissociation. The rate constant depends on the reaction free energy and reorganization energy, the bound state energies and wave functions in the initial proton surface, and the parameters of the proton final state repulsive surface. The rate constant can be quite large and should provide a reaction pathway competitive with consecutive electron and proton transfer.