Dissociative adsorption of O 2 on Ag(111)

Abstract

Thermal energy atom scattering (TEAS) is used to determine the initial sticking probability S 0 for dissociative chemisorption of O 2 on Ag(111). Mixed beams of He and O 2 are used to study S 0 as a function of energy of the molecule (MBTEAS). At thermal energies S 0 is about 3.5×10 −6. It drops to immeasurably low values with increasing energy and rises to about 1×10 −5 on further increase of the incident energy (1.6 eV at 45°). S 0 seems to scale with E n. Two different mechanisms are responsible for sticking. At low energies physisorption-mediated sticking is dominant, and at high energies sticking via an activated precursor prevails. The adsorbed oxygen is removed in a first-order process with a decay time of 1000 s, as determined from the time dependence of the TEAS signal.