A simulation study of the chemisorption dynamics of molecular hydrogen on the Ni(111) surface

The dissociative chemisorption of an H-2 beam on the Ni(111) surface was simulated by running quasi classical trajectories, using for the molecule-surface interaction a LEPS potential built from ab initio results available for the H atom interacting with Ni clusters. The adsorption of H-2 is an activated process, with barrier of 200 meV in the entrance channel, followed by a non-dissociative chemisorption well in the exit channel which is separated by a narrow saddle point region from the well of adsorbed H atoms. In the rigid surface approximation, the dependence of the dissociative chemisorption probability, P-a, on the H-2 collision energy, E(col), is described by an S-shaped curve. When the nickel atoms of the impact region of H-2 at the surface are allowed to move (generalized Langevin equations in the ghost atoms formulation were used), P-a increases with E(col) along a smooth curve comparable to that observed in molecular beam experiments. The results of a study of the influence on P-a of the H-2 internal and translational energies, of the surface temperature, of the beam incident angle and of the surface corrugation are presented and discussed.