Ab initio molecular dynamics study of H2 adsorption on sulfur- and chlorine-covered Pd(100)

The adsorption of molecular hydrogen on sulfur- and chlorine-covered Pd(100) in a (2 × 2) geometry is studied by ab initio molecular dynamics simulations. The potential energy surfaces of H2/S(2 × 2)/Pd(100) and H2/Cl(2 × 2)/Pd(100) are rather similar. Consequently, also the dependence of the sticking probability on incident kinetic energy, angle of incidence and internal excitations are very close. For H2/S(2 × 2)/Pd(100), previous results obtained on an interpolated ab initio potential energy surface are confirmed, except for the dependence of the sticking probability on the initial rotational state which exhibits a surprising rotational enhancement. Discrepancies with respect to the experiment which remain are discussed. In the simulations, several subsurface penetration events have been found, preferentially close to the sulfur or chlorine adatoms, respectively. This is explained by lower barriers caused by the destabilization of hydrogen adsorption close to the repulsive adatoms.