Molecular-beam scattering of O2 and Ar from Ag(111)

Abstract

A well-collimated supersonic beam of Ar or O2, optionally seeded in He, collides with a Ag(111) surface. The resulting momentum distribution of the scattered particles is measured using a rotatable quadrupole mass spectrometer and time-of-flight (TOF) techniques. Comparing O2 with Ar shows that O2 behaves in direct scattering from Ag(111) very much like the monoatomic Ar. Both Ar and O2 scattering can be described rather well by a hard-cube model, although the parallel momentum is not conserved. The agreement between O2 and Ar suggests the existence of a potential barrier of at least 170 meV between the physisorbed and the chemisorbed O2 state on the Ag(111) surface.