Oxygen sticking on Pd(111): double precursors, corrugation and substrate temperature effects

The initial sticking coefficient for oxygen on Pd(lll) was measured as a function of O-2 translational energy, angle of incidence and substrate temperature. The results indicate that the O-2 dissociation involves sequential population of a physisorbed and a chemisorbed precursor state at low translational energies and direct molecular chemisorption at high energies. No direct dissociation was observed. A strong angular dependence in the sticking coefficient at high translational energies suggests considerable corrugation in the activation barrier for molecular chemisorption. An observed enhancement in the sticking with increasing substrate temperature is consistent with a reduction in this corrugation. (C) 1998 Elsevier Science B.V.