Low translational energy mechanisms in the dissociative chemisorption of methane on iridium and platinum surfaces

Recent molecular beam studies of methane dissociative chemisorption on Ir(1 1 0), Ir(1 1 1) and Pt(1 1 0) surfaces show evidence of a low translationa l energy pathway to dissociation that had not been seen previously for meth ane dissociation on any transition metal surface. Earlier molecular beam st udies on a variety of transition metal surfaces indicated only a direct dis sociative mechanism for methane dissociation, which is active only at high translational energies. Recent studies on Ir and Pt show that at low transl ational energies the dissociative chemisorption probability decreases as th e translational energy increases in contrast to the behavior at higher tran slational energies, where the direct mechanism is known to be dominant and the chemisorption probability increases with increasing translational energ y. The exact mechanism of this low energy pathway is under debate and has b een described as either a trapping-mediated mechanism or a steering-assiste d direct mechanism. (C) 2001 Elsevier Science B.V. All rights reserved.