Electron-hole pair mechanism for excitation of intramolecular vibrations in molecule-surface scattering

Recently excitation of the ν = 1 vibrational state of NO scattered from Ag(111) has been observed. The measured excitation probability goes as the Boltzmann factor exp( -ℏomega;0 kBTs) where ω0 is the vibration frequency and TS the surface temperature. We show that with reasonable assumptions the data can be explained by a mechanism in which vibrational excitation results from de-excitation of a hot electron-hole pair in the metal, the coupling to the molecular vibration being via electrons hopping in and out of the π* orbital of NO. The "mechanical" mechanism is ruled out by the absence of excitation at low temperature. © 1986.