Abstract

We report vibrational excitation of CO from its ground (v = 0) to first excited (v = 1) vibrational state in collision with Au(111) at an incidence energy of translation of E(I) = 0.45 eV. Unlike past work, we can exclude an excitation mechanism involving temporary adsorption on the surface followed by thermalization and desorption. The angular distributions of the scattered CO molecules are narrow, consistent with direct scattering occurring on a sub-ps time scale. The absolute excitation probabilities are about 3% of those expected from thermal accommodation. The surface temperature dependence of excitation, which was measured between 373 and 973 K, is Arrhenius-like with an activation energy equal to the energy required for vibrational excitation. Our measurements are consistent with a vibrational excitation mechanism involving coupling of thermally excited electron-hole pairs of the solid to CO vibration.

Highlights

  • A prerequisite to developing a better understanding and predictive theories of surface chemistry is development of a corresponding understanding and theoretical description of the complex sequence of processes often involved in a surface chemical reaction

  • The absolute excitation probabilities are about 3% of those expected from thermal accommodation

  • Our measurements are consistent with a vibrational excitation mechanism involving coupling of thermally excited electron–hole pairs of the solid to CO vibration

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Summary

Introduction

A prerequisite to developing a better understanding and predictive theories of surface chemistry is development of a corresponding understanding and theoretical description of the complex sequence of processes often involved in a surface chemical reaction. A key feature that distinguishes surface chemistry from gas-phase chemistry is energy flow between the translational and internal degrees of freedom of a reacting molecule and the elementary excitations of the solid. Excited electronic states of the molecule, high in energy in the gas-phase, may be stabilized in the vicinity of the surface. Local spin conservation at the reaction center may even be destroyed by rapid two electron transfer (as well as - LÁ- S coupling).. Local spin conservation at the reaction center may even be destroyed by rapid two electron transfer (as well as - LÁ- S coupling).13 Another fundamental consideration: one must confront the breakdown of the Born–Oppenheimer (electronically adiabatic) approximation, which forms the basis of most computational chemistry.. Local spin conservation at the reaction center may even be destroyed by rapid two electron transfer (as well as - LÁ- S coupling). Another fundamental consideration: one must confront the breakdown of the Born–Oppenheimer (electronically adiabatic) approximation, which forms the basis of most computational chemistry. heavy atom motion (vibration, translation and rotation) may, in principle, couple with this complex web of electronic interactions

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