CO on Fe(110): an angle-resolved photoemission study

Abstract

CO chemisorption on Fe(100) at 80 K was reinvestigated by angle-resolved ultraviolet photoemission spectroscopy with synchrotron radiation. At 0.25 L, the CO 5σ peak and the CO 4σ peak are observed at 7.5 and 10.5 eV below the Fermi level, and they shift to 8.3 and 10.7 eV respectively, as the coverage increases up to 3.0 L. In contrast to previous observations for CO on Fe(100) [Phys. Rev. B 27 (1983) 3338] where the 1π − 5σ separation was considerably larger (~1.5 eV), the 1π and 5σ peaks are not observed separately as usually. Their separation is found to be ~0.5 eV. The lower binding-energy peak previously assigned to CO 1π emission is due to oxygen contamination. The present data also indicate that the orientation of the CO axis undergoes a two-stage transition depending on the amount of CO exposure: inclined (⩽ 0.5 L) → upright (~2 L) → inclined (4 L).