Specific features of the formation of co-adsorption layers on metal surfaces with the participation of simple molecules: NH3 + CO on Pt(111)

Abstract

The co-adsorption of ammonia and carbon monoxide on the Pt(111) surface was studied at temperatures <300 K using high-resolution electron energy loss spectroscopy (HREELS). The state of ammonia and carbon monoxide molecules in the co-adsorption layer was established to differ significantly from their state in individual adsorption layers. The adsorption of CO on a clean surface occurs with the primary filling of single-bound terminal sites, whereas the bridging sites are filled preferably by CO molecules in the presence of NH3,ads. The symmetry axis of ammonia molecules adsorbed on the clean surface is parallel to the normal to the surface, whereas in the co-adsorption layers the interaction with COads molecules results in the deviation of the symmetry axis toward the surface. Presumably, the observed changes in the state of adsorbed molecules are due to the donor-acceptor interaction inducing the electron density transfer from ammonia molecules across the metal surface to CO molecules.