Efficient vibrational and translational excitations of a solid metal surface: State-to-state time-of-flight measurements of HCl(v=2,J=1) scattering from Au(111)

We report high resolution state-to-state time-of-flight (TOF) measurements for scattering of HCl(v=2, J=1) from a Au(111) single crystal surface for both vibrationally elastic (v=2 -> 2) as well as inelastic (v=2 -> 1) channels at seven incidence energies between 0.28 and 1.27 eV. The dependences of the TOF results on final HCl rotational state and surface temperature are also reported. The translational energy transferred to the surface depends linearly on incidence energy and is close to the single surface-atom impulse (Baule) limit over the entire range of incidence energies studied. The probability of vibrational relaxation is also large. For molecules that relax from v=2 to v=1, the fraction of vibrational energy that is transferred to the surface is approximately 74%. We discuss these observations in terms of an impulse approximation as well as the possible role of translational and vibrational excitations of electron-hole pairs in the solid.