Electronically nonadiabatic dynamics can be important in collisions of molecules at surfaces; for example, when vibrational degrees of freedom of molecules are coupled to electron-hole-pair (EHP) excitation of a metal. Such dynamics have been inferred from a host of observations involving multiquantum relaxation of NO molecules scattered from metal surfaces. Electron transfer forming transient NO– is thought to be essential to the nonadiabatic coupling. The question remains: is this behavior usual? Here, we present final vibrational state distributions resulting from the scattering of CO­(v i = 17) from Au(111), which exhibits significantly less vibrational relaxation than NO­(v i = 16). We explain this observation in terms of the lower electron affinity of CO compared to NO, a result that is consistent with the formation of a transient CO– ion being important to CO vibrational relaxation.

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We report vibrational relaxation probabilities for CO(v = 17) scattered from Ag(111) and compare our results to studies on other molecule–surface systems, which indicates a clear dependence of the relaxation probability on the work function of the surface and the electron binding energy of the molecule.