Direct-inelastic and trapping-desorption scattering of N₂ and CH₄ from Pt(111)

Angle and velocity distributions for supersonic chopped beams of N2 and CH4 scattered from clean close-packed Pt(111) surfaces are reported. For specular direct-inelastic scattering N2 and CH4 velocity distributions can be characterized by empirical relationships used for Ar scattering. For instance, for specular scattering the following relation is found for Ar, N2 and CH4: 〈KEf〉 = A(KEi) + B(2kTs), where 〈KEf〉 is the average final kinetic energy, KEi is the incident kinetic energy and Ts is the surface temperature. The beam and surface temperature independent coefficients A and B are, respectively: Ar 0.87, 0.17; N2 0.79, 0.19 and CH4 0.84, 0.25. Unlike Ar, N2 desorbs from Pt with a Maxwell-Boltzmann velocity distribution near the surface temperature. Qualitatively the trapping probabilities for these molecules on Pt(111) are ordered: Xe > N2 > CH4> Ar. © 1983.