Poisoning of hydrogen dissociation at Pd (100) by adsorbed sulfur studied by ab-initio quantum dynamics and ab-initio molecular dynamics

We report calculations of the dissociative adsorption 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 ab-initio potential-energy surface (PES) is found to be very strongly corrugated. In particular, we discuss the influence of tunneling, zero-point vibrations due to the localization of the wave function of the nuclei when narrow valleys of the PES are passed, steering of the approaching H-2 molecules towards low-energy barrier configurations, and the important role of subsurface absorbates for the hydrogen dissociation. It is shown that "established" concepts derived from low-dimensional dynamical studies are not necessarily valid in a high-dimensional treatment. (C) 1998 Elsevier Science B.V. All rights reserved.