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 translational energy pathway to dissociation that had not been seen previously for methane dissociation on any transition metal surface. Earlier molecular beam studies on a variety of transition metal surfaces indicated only a direct dissociative mechanism for methane dissociation, which is active only at high translational energies. Recent studies on Ir and Pt show that at low translational energies the dissociative chemisorption probability decreases as the translational energy increases in contrast to the behavior at higher translational energies, where the direct mechanism is known to be dominant and the chemisorption probability increases with increasing translational energy. The exact mechanism of this low energy pathway is under debate and has been described as either a trapping-mediated mechanism or a steering-assisted direct mechanism. (C) 2001 Elsevier Science B.V. All rights reserved.