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

摘要

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 lang;Errang; depends linearly on the surface temperatureEs(=Ts) and the incident kinetic energy normal to the surfaceEnaccording to lang;Errang;=a(En+lang;Ewprime;rang;)+bEs. The three parametersa,b, and lang;Eprime;wrang; are constants independent ofEnandEs. Arguments are presented showing that lang;Eprime;wrang; is some measure of the average NO/Ag(111) well depth. For the OHgr;=1/2 fine structure component we estimate that lang;Eprime;wrang;=2850plusmn;450 K (245plusmn;40 meV),a=0.88plusmn;0.009, andb=0.18plusmn;0.04 while for OHgr;=3/2, lang;Eprime;wrang;=2080plusmn;150 K (180plusmn;13 meV),a=0.132plusmn;0.005, andb=0.11plusmn;0.02. The results are compared to the predictions of onehyphen;dimensional impulsive models of gashyphen;surface scattering. These models are able to describe qualitatively the dependence of lang;Errang; onEnandEsbut only when trapping fractions that are incompatible with experiment are predicted simultaneously.