Activated dissociation of H2 on the Cu(001) surface: The role of quantum tunneling

Abstract

The activation and dissociation of hydrogen molecules (H2) on the Cu(001) surface are studied theoretically. Using first-principles calculations, the activation barrier for the dissociation of H2 on Cu(001) is determined to be ∼ 0.59 eV in height. It is found that the electron transfer from the copper substrate to H2 plays a key role in the activation and breaking of the H–H bond, and the formation of the Cu–H bonds. Two stationary states are identified at around the critical height of bond breaking, corresponding to the molecular and the dissociative states, respectively. Using the transfer matrix method, we also investigate the role of quantum tunneling in the dissociation process along the minimum energy pathway (MEP), which is found to be significant at or below room temperature. At a given temperature, the tunneling contributions due to the translational and the vibrational motions of H2 are quantified for the dissociation process. Within a wide range of temperature, the effects of quantum tunneling on the effective barriers of dissociation and the rate constants are observed. The deduced energetic parameters associated with the thermal equilibrium and non-equilibrium (molecular beam) conditions are comparable to experimental data. In the low-temperature region, the crossover from classical to quantum regime is identified.