Direct inelastic scattering of nitric oxide from clean Ag(111): Rotational and fine structure distributions

Abstract

The internal state distribution of scattered NO is determined by laser fluorescence excitation spectroscopy when a pulsed, supersonically cooled beam of NO is incident upon the (111) face of a clean Ag single crystal. It is found that the mean rotational energy 〈Er〉 depends linearly on the surface temperature Es(=Ts) and the incident kinetic energy normal to the surface En according to 〈E r〉=a(En+〈E′w〉)+bE s. The three parameters a, b, and 〈E′w〉 are constants independent of En and Es. Arguments are presented showing that 〈E′w〉 is some measure of the average NO/Ag(111) well depth. For the Ω=1/2 fine structure component we estimate that 〈E′w〉=2850±450 K (245±40 meV), a=0.88±0.009, and b=0.18±0.04 while for Ω=3/2, 〈E′w〉=2080±150K (180±13 meV), a=0.132±0.005, and b=0.11±0.02. The results are compared to the predictions of one-dimensional impulsive models of gas-surface scattering. These models are able to describe qualitatively the dependence of 〈E r〉 on En and Es but only when trapping fractions that are incompatible with experiment are predicted simultaneously. © 1983 American Institute of Physics.