Incidence energy dependent state-to-state time-of-flight measurements of NO(v = 3) collisions with Au(111): the fate of incidence vibrational and translational energy.

We report measurements of translational energy distributions when scattering NO(vi = 3, Ji = 1.5) from a Au(111) surface into vibrational states vf = 1, 2, 3 and rotational states up to Jf = 32.5 for various incidence energies ranging from 0.11 eV to 0.98 eV. We observed that the vibration-to-translation as well as the translation-to-rotation coupling depend on translational incidence energy, EI. The vibration-to-translation coupling, i.e. the additional recoil energy observed for vibrationally inelastic (v = 3 → 2, 1) scattering, is seen to increase with increasing EI. The final translational energy decreases approximately linearly with increasing rotational excitation. At incidence energies EI > 0.5 eV, the slopes of these dependencies are constant and identical for the three vibrational channels. At lower incidence energies, the slopes gradually approach zero for the vibrationally elastic channel while they exhibit more abrupt transitions for the vibrationally inelastic channels. We discuss possible mechanisms for both effects within the context of nonadiabatic electron-hole pair mediated energy transfer and orientation effects.