A THEORETICAL-STUDY OF THE ADSORPTION DYNAMICS OF HYDROGEN ON NI(111) SURFACE

The dissociative chemisorption of a beam of molecular hydrogen on the Ni(111) surface was simulated by classical trajectories calculations, using an LEPS potential for the interaction of H-2 with Ni(111) surface built from ab initio results available for the H atom interacting with Ni clusters. In the most favoured reaction path, the adsorption of H-2 is activated, with a small barrier (140 meV) in the entrance channel, followed by a small well in the exit channel, separated by a narrow saddle point region from the H-H bond breaking well. The results show that (a) the dissociative adsorption probability P-a increases steadily with collision kinetic energy E(col), showing a trend in good agreement with nozzle beams experiments; (b) the H-2 vibrational energy is less important than the translational one in favouring adsorption with H-H bond breaking; (c) P-a increases when the incident polar angle of the beam increases from theta = 0 degrees up to theta = 25-30 degrees, and then it decreases rapidly to zero when theta increases from 25-30 degrees to 60 degrees; (d) azimuthal corrugation effects on P-a are present at incident angles greater than 15 degrees.