Synchrotron photoemission study of CO chemisorption on Cr(110)

Angle-integrated ultraviolet photoemission studies of carbon monoxide chemisorption on Cr(110) confirm the sequential population of two electronically inequivalent molecular binding states (${\alpha }_{1\mathrm{-}}$CO and ${\alpha }_{2\mathrm{-}}$CO) at 90 K. These are distinguished by differences in the CO 4σ binding energies (Δ$E_B$=0.8 eV) and photoemission cross sections. Work-function measurements indicate that the surface dipole moment associated with ${\alpha }_1$-CO is significantly less than that for ${\alpha }_2$-CO. CO/O interaction data exhibit oxygen-induced ${\alpha }_1$-CO site blocking and ${\alpha }_{1\mathrm{-}}$CO→${\alpha }_2$-CO binding mode conversion. These results support current models for the CO binding geometries on Cr(110) and related binding states on Fe (100) and Mo(100).