Dynamics of hydrogen dissociation at the sulfur-covered Pd(100) surface

We report calculations of the dissociative adsorption and associative desorption of H-2 at Pd(100) covered with 1/4 monolayer of sulfur using quantum dynamics as well as molecular dynamics and taking all six degrees of freedom of the two H atoms fully into account. The potential energy surface (PES) has been derived from density-functional theory calculations. The absolute value of the calculated sticking coefficient turns out to be at variance with a molecular beam experiment. However, the relative change of the sticking coefficient as a function of the angle of incidence as well as the mean kinetic energy and the rotational alignment of desorbing hydrogen molecules agree quite well with the experiment. This indicates that the calculated PES reproduces the most favorable reaction path, but that in the experiment the sulfur adlayer was probably not very well ordered.