CO ON FE(110) - AN ANGLE-RESOLVED PHOTOEMISSION-STUDY

CO chemisorption on Fe(l 10) at 80 K was reinvestigated by angle-resol ved ultraviolet photoemission spectroscopy with synchrotron radiation. At 0.25 L, the CO 5sigma peak and the CO 4sigma 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(110) [Phys. Rev. B 27 (1983) 3338] where the 1pi-5sigma separation was considerably larger (approximatel y 1.5 eV), the 1pi and 5sigma peaks are not observed separately as usu ally. Their separation is found to be approximately 0.5 eV. The lower binding-energy peak previously assigned to CO 1pi emission is due to o xygen contamination. The present data also indicate that the orientati on of the CO axis undergoes a two-stage transition depending on the am ount of CO exposure: inclined (less-than-or-equal-to 0.5 L) --> uprigh t (approximately 2 L) --> inclined (4 L).