Observation of Direct Vibrational Excitation in Gas-Surface Collisions: NO on Ag(111)

Vibrationally excited NO molecules have been observed in the scattering of $\mathrm{NO}\mathrm{}(v=0\mathrm{})\mathrm{}$ from Ag(111). A direct mechanism is inferred based on the observation of $v=1\mathrm{}$ angular distributions, which are quasispecular, and rotational-state distributions, which depend on beam energy. Vibrational excitation is found to depend strongly on surface temperature, $T_S$, and relatively weakly on incident kinetic energy, $E$, reaching (∼7±5)% at $T_S=760\mathrm{}$ K and $E=120\mathrm{}$ kJ ${\mathrm{mol}}^{-1\mathrm{}}$. These results are discussed in terms of an electronic mechanism for vibrational excitation.