Observation of direct multiquantum vibrational excitation in gas-surface scattering: NH3 on Au(111)

Vibrationally excited NH3 molecules are observed in the scattering of NH3 (v = 0) from Au(111). We observe up to three quanta of vibrational excitation in the ν2 ''umbrella'' vibrational mode of NH3. The vibrational excitation probability scales linearly with the kinetic energy of the incident beam above a threshold energy corresponding to the quanta excited, and is independent of the surface temperature, T/sub s/, over the range 300 K≤T/sub s/≤800 K. These results are discussed in terms of an electronically adiabatic collisional mechanism for vibrational excitation