Electronic friction in proton tunneling at the electrochemical interface

: We consider the effects of electronic friction (nonadiabaticity) on the tunneling of a proton from an H3O+ in water to the surface of a metal electrode. The final state is a hydrogen atom adsorbed on the surface of the metal. We use a simple model Hamiltonian for the description of the process and calculate the tunneling probability using the semiclassical approaches of Miller [J. Chem. Phys. 62, 1899 (1975)]. The continuum of electron-hole excitations is accounted for by treating them as bosons. We show that typically, tunneling probability can be decreased by one to two orders of magnitude by coupling to electron-hole excitations. We also report on the effect of isotopic substitution on this rate. While our analysis is specifically for an electrochemical situation, the results are of general validity and imply a decrease in tunneling probability, due to electronic friction for the proton in cases where tunneling occurs in the presence of a metal surface for example, atom transfer in STM experiments