Vibrational Spectra of Species Adsorbed on Surfaces: Forms of Vibrations and Selection Rules for Regular Arrays of Adsorbed Species

In this paper we describe systematically the forms, symmetries, and selection rules for the normal modes of vibration of a number of examples of surface-adsorbed species. The chosen cases are discussed for adsorption both on isolated sites and in regular arrays of surface sites such as are occupied at higher coverage. For this purpose the Site Group and Factor Group (Correlation Field) approach to the vibrations of regular 3-dimensional lattices is adapted to the 2-dimensional systems. For simplicity the examples chosen are mainly monatomic and diatomic species adsorbed in various ways on specific sites of (111), (100), or (110) planes of metals with face-centered cubic lattices. The selection rules discussed refer to activities in infrared, Raman, or electron energy loss spectroscopy (dipolar and impact scattering mechanisms) and distinguish between adsorption on insulating and conducting (metal) surfaces. The examples chosen for regular arrays all refer to cases where experimental results (mainly from electron energy loss spectroscopy) are available in the literature, where they have been discussed mainly at the site group level.