Mechanism of the dissociative chemisorption of methane over Ir(110): Trapping-mediated or direct?

A controversy exists regarding the dominant mechanism in the reaction of methane over transition metals. We present new insight regarding this subject by: (1) providing the first unambiguous evidence for the chemisorption of methane by a trapping-mediated mechanism; (2) demonstrating, with unprecedented accuracy, agreement between bulb measurements of reaction probability and determinations employing molecular beam techniques, and (3) quantifying the contributions of differing mechanisms as a function of experimental conditions. Our results show conclusively that a trapping-mediated mechanism dominates dissociative chemisorption of methane over Ir(110) at low gas temperatures and that a direct mechanism dominates at high gas temperatures.