Anharmonic damping of adsorbate vibrational modes

We present calculations of the anharmonic damping of adsorbate vibrational modes, for modes with frequency below twice the maximum substrate phonon frequency. In this case, two-phonon processes dominate the anharmonic coupling of the adsorbate to the substrate. Explicit results for the magnitude and temperature variation of this damping are presented, for oxygen and sulfur adatoms on the Ni(100) and Ni(111) surface and for top bonded CO on Ni(100).