Adsorption and desorption of CO on W(110) surfaces

The adsorption of CO on W(110) surfaces was studied using thermal desorption spectroscopy (TDS), and core and valence level spectroscopy. At 120 K, CO forms a tilted structure at lower coverages (α₁), whereas it adsorbs normal to the surface at higher coverages (α₂). Tilted structures have been suggested to be precursors of dissociative chemisorption; however, experimental evidence is provided for the non-dissociative chemisorption of CO at temperatures above 900 K (which is referred to as the β-state): TDS shows first order desorption kinetics. The core and valence level spectra of O/W(110) and those of β-CO/W(110) are different. Most importantly, the 4σ molecular orbital of CO can be identified in the valence level spectra of the β-CO.