Trapping-desorption scattering of argon from Pt(111)

Abstract

Measurements of the velocity and angular distributions for trapping-desorption scattering of argon from a clean, well characterized Pt(111) single crystal are reported. For certain experimental conditions, both the characteristic velocity and angular distributions deviate markedly from that predicted using equipartition arguments (i.e., a Maxwellian flux distribution in velocity and a cosine distribution in angle). The average kinetic energy for the flux exiting normal to the surface at 100 K is only 80% of that expected for a Maxwellian at TS. This kinetic energy deficit decreases and approaches zero as the detector is rotated away from the surface normal. The angular flux distribution is found to be broader than cosine. These results are discussed in terms of microscopic reversibility which permits estimates of the velocity dependent condensation coefficient to be obtained.