Abstract
Using molecular beam cooled samples and quantum state-selective detection, we observe v = 0 → 1 vibrational transitions when HCl (v = 0) collides with an Ag(111) surface and derive both the incidence energy and surface temperature dependence of the transition probability. Our observations reveal that both electronically adiabatic and non-adiabatic mechanisms are at play in this inelastic process. A comparison to other systems shows similarities and trends that are consistent with an electron transfer mechanism forming a transient HCl-. For example, the electronically nonadiabatic coupling is stronger than for HCl scattering from Au, where the solid's work function is higher. HCl differs from other systems in that dissociation is possible over a low barrier. Vibrationally inelastic v = 1 → 2 transitions could not be seen when HCl (v = 1) collides with an Ag(111) surface. We suggest that scattering events, where HCl (v = 1) is subject to dynamical influences that increase its vibrational energy, lead efficiently to dissociation before the HCl (v = 2) molecule can escape the surface. This system appears to be an excellent candidate to study electronically nonadiabatic effects in dissociative adsorption.
Highlights
The Born–Oppenheimer approximation (BOA), introduced almost a century ago,1 still forms the basis of the majority of theoretical treatments of chemistry
The key quantities that determine the energetics of transient anion formation are the solid’s work function and the molecule’s vertical electron binding energy, which is related to its electron affinity
Similar to the observations for HCl scattering from Au(111),27 the intensity of the HCl (υ = 0) Resonance Enhanced Multi-Photon Ionization (REMPI) signal decreases only slightly with an increase in surface temperature, while the REMPI signal from HCl (υ = 1) is strongly enhanced
Summary
The Born–Oppenheimer approximation (BOA), introduced almost a century ago, still forms the basis of the majority of theoretical treatments of chemistry. Molecular dynamics simulation using electronic friction to characterize BOA failure successfully reproduced translational inelasticity of H and D collisions at metal surfaces as well as the magnitude of the isotope effect in chemicurrent experiments.. The magnitude of the electronically nonadiabatic interaction is believed to be enhanced when a transient negative ion can be formed.. The key quantities that determine the energetics of transient anion formation are the solid’s work function and the molecule’s vertical electron binding energy, which is related to its electron affinity.. The key quantities that determine the energetics of transient anion formation are the solid’s work function and the molecule’s vertical electron binding energy, which is related to its electron affinity.23 Another important question is how close the molecule can approach the surface, as image charge stabilization of the anion decreases with distance from the surface. Incidence translational energy enhances electronically nonadiabatic vibrational excitation, even scitation.org/journal/jcp though direct translational to vibrational energy transfer is unimportant
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