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

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 〈Er〉=a(En+〈Ew′〉)+bEs. 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±150 K (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 〈Er〉 on En and Es but only when trapping fractions that are incompatible with experiment are predicted simultaneously.