A nonempirical molecular-orbital theory of the relaxation of excited vibrations at metal surfaces by energy transfer to conduction electrons is described. With use of ab initio calculations on cluster models of the adsorbate-surface system, the lifetimes of all four local modes of CO on Cu(100) are obtained. The calculated lifetimes are in qualitative agreement with experiment, and can be understood in terms of simple orbital interpretations of the nonadiabatic vibrational relaxation mechanisms.

• Received 18 December 1991

DOI:https://doi.org/10.1103/PhysRevB.46.1853