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Zusammenfassung:
We report vibrational excitation of CO from its ground (v = 0) to first excited (v = 1) vibrational state in
collision with Au(111) at an incidence energy of translation of EI = 0.45 eV. Unlike past work, we can
exclude an excitation mechanism involving temporary adsorption on the surface followed by thermalization
and desorption. The angular distributions of the scattered CO molecules are narrow, consistent with direct
scattering occurring on a sub-ps time scale. The absolute excitation probabilities are about 3% of those
expected from thermal accommodation. The surface temperature dependence of excitation, which was
measured between 373 and 973 K, is Arrhenius-like with an activation energy equal to the energy required
for vibrational excitation. Our measurements are consistent with a vibrational excitation mechanism
involving coupling of thermally excited electron–hole pairs of the solid to CO vibration.