The interaction of carbon monoxide with the pure and potassium-promoted Cu(332) surface

Abstract

The adsorption behaviour of the KCO coadsorbate system has been studied at an adsorption temperature of 95 K on the vicinal Cu(332) surface. Thermal desorption spectroscopy experiments show that the K adatoms disturb the electrostatic potential induced by the steps of the vicinal surface, and therefore the CO molecules adsorbed on step sites are the first to be influenced by the coadsorbed alkali. With K present on the surface in a metal-like form, a strong KCO interaction is evidenced by a stabilization of the adlayer up to temperatures >500 K. Work-function change measurements reveal a change in the bonding of CO towards the precovered surface: the results cannot be interpreted using a simple Blyholder model, but imply a direct interaction of potassium with the 1π orbital of CO. The existence of this direct interaction gives rise to an abolition of the (1π + 5σ) degeneration in the CO-induced states in the UV-photoelectron spectra.