THE INFLUENCE OF MOLECULAR ROTATION ON THE DIRECT SUBSURFACE ABSORPTION OF H-2 ON PD(111)

Within the generalized gradient approximation (GGA) of density functio nal theory (DFT) we have calculated a three-dimensional (3D) potential energy surface (PES) including an angular degree of freedom for a H-2 molecule interacting with a Pd(lll) surface. There is an entrance cha nnel barrier (approximate to 0.09 eV) to both dissociative chemisorpti on and direct subsurface absorption, but after this barrier is crossed direct subsurface absorption can proceed almost without a barrier. 3D quantum mechanical wave packet calculations incorporating the rotatio n of H-2 in a plane perpendicular to the surface show a large part of the hydrogen going directly subsurface even at low incident kinetic en ergies. The wave packet calculations also show that in the low energy regime rotation inhibits direct subsurface absorption at low j(0) and promotes it at high j(0). (C) 1998 American Institute of Physics.