Observation of Direct Multiquantum Vibrational Excitation in Gas-Surface Scattering: NH3on Au(111)

Vibrationally excited N${\mathrm{H}}_3$ molecules are observed in the scattering of N${\mathrm{H}}_3$ ($v=0\mathrm{}$) from Au(111). We observe up to three quanta of vibrational excitation in the ${\nu }_2$ "umbrella" vibrational mode of N${\mathrm{H}}_3$. 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, $T_s$, over the range $300 \mathrm{K}\le T_s\le 800 \mathrm{K}$. These results are discussed in terms of an electronically adiabatic collisional mechanism for vibrational excitation.