Spectroscopy of Surface Vibrations

Abstract

The intention of this paper is to give a brief account of recent progress in the study of vibrational spectra of atoms and molecules adsorbed on single crystal surfaces of metals. Such adsorption systems offer unique possibilities to investigate ordered arrangements of adsorbed species and the spectroscopic information achieved can be discussed in terms of structural models suggested from electron diffraction analysis (LEED, RHEED) and electron structure models derived from electron spectroscopic analysis. Vibrational spectroscopy is certainly highly sensitive to the adsorption site symmetry and there exist a vast number of important structural problems related to different adsorbate structure — substrate surface configurations. At present most such analysis work is performed empirically relying on vibrational spectroscopic data for known molecules and solids. Chemisorption on metal surfaces constitute, however, a very metal rich chemical phase and specific coordinations do occur, that are never met in other systems. For that purpose vibrational frequencies derived from adsorption energy curves calculated for high symmetry adsorption sites would resolve ambiquities. Such calculations are within the grasp of modern chemisorption theory. The analytical power of vibrational spectroscopy as applied to chemisorption is of course not only related to questions concerning the adsorption site (which may be most relevant for atoms and simple molecules) but most importantly to the capability of identifying species formed during any surface reaction /1/.