Effect of Lattice Motion on Dissociation and Recombination Rates of H2 on Ni(100) Surface

Abstract

The rate constants and kinetic isotope effects of H2 dissociation and recombination on Ni(100) surface are calculated by using the quantum instanton method, together with path integral Monte Carlo and adaptive umbrella sampling techniques. The Ni(100) surface model containing 104 nickel atoms and the potential energy surface based on the embedded diatomics in molecules are used. For the H2 dissociation, the results on the rigid lattice are consistent with experimental data. Compared to the rigid lattice, the classical and quantum motions of the lattice further enhance the dissociation rates by 18 and 49% at 300 K. The calculated kinetic isotope effects show that the H2 always has the largest rate, while the D2 has the smallest one. For the H2 recombination, however, the effects of lattice motions on the rates are different from those for the dissociation, that is, compared to the rigid lattice, both the classical and quantum motions of the lattice lower the recombination rates. The possible mechanism is analyzed by the corresponding free energy profiles.