Vibrational energy and phase relaxation at surfaces

An estimate of the contribution to the linewidth of vibrations at surfaces from vibrational energy and phase relaxation is presented. It is found that phase relaxation is not important, while decay via emission of two phonons is very important when energetically possible. Thus the Ni-CO stretching vibration for CO on Ni (100) is probably damped via the emission of two phonons. High-frequency modes, such as the C-O stretching vibration, are probably damped via the excitation of electron-hole pairs.