Vibrational Damping of Adsorbed Molecules: Methoxide on Cu(100)

The lifetimes of the C-H and C-D stretch vibrational modes of methoxide adsorbed on Cu(100) have been measured by infrared spectroscopy. It is shown that the damping of these vibrational states is caused by excitation of electron-hole pairs in a region very close to the vibrating molecule. It is argued that the electron-hole pairs are excited because a resonance around the Fermi level fills and empties during the vibration.