In this work we seek to examine the nature of collisional energy transfer between HCl and Au(111) for nonreactive scattering events that sample geometries near the transition state for dissociative adsorption by varying both the vibrational and translational energy of the incident HCl molecules in the range near the dissociation barrier. Specifically, we report absolute vibrational excitation probabilities for HCl(v = 0 → 1) and HCl(v = 1 → 2) scattering from clean Au(111) as a function of surface temperature and incidence translational energy. The HCl(v = 2 → 3) channel could not be observed—presumably due to the onset of dissociation. The excitation probabilities can be decomposed into adiabatic and nonadiabatic contributions. We find that both contributions strongly increase with incidence vibrational state by a factor of 24 and 9, respectively. This suggests that V-T as well as V-EHP coupling can be enhanced near the transition state for dissociative adsorption at a metal surface. We also show that previously reported HCl(v = 0 → 1) excitation probabilities [Q. Ran et al., Phys. Rev. Lett. 98, 237601 (2007)]—50 times smaller than those reported here—were influenced by erroneous assignment of spectroscopic lines used in the data analysis.
In Ref. 17 we have shown that the calculated barrier height might be too low. In any case, the time-of-flight data presented in the supplementary material show that approximately half the translational energy is lost to surface phonon excitation during the scattering process. Thus, the mean incident translational energies used in this study alone are not high enough to overcome the barrier.
Based on previously unpublished data for NO/Au(111) v = 2 → 3 excitation. Data, analysis, and further comparison are given in Section III of the supplementary material.
Unfortunately we do not have data for exactly the same incidence translational energy. Since we approximatively determine the derivative of the nonadiabatic A-factor with respect to the incidence translational energy in Table III, this comparison should still be valid.