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.
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We gratefully acknowledge the financial support from the Department of Energy Office of Basic Energy Sciences, under Grant No. DE-FG02-03ER15441, as well as the Partnership for International Research and Education—for Electronic Chemistry and Catalysis at Interfaces—NSF Grant No. OISE-0530268.