High-Resolution C1sand O1sCore-Excitation Spectroscopy of Chemisorbed, Physisorbed, and Free CO

High-resolution soft-x-ray excitation spectra are reported for free CO, CO condensed on Au at ∼ 20 K, and CO chemisorbed on Ni(111). Chemisorption increases dramatically the widths of the C and O $1s\to 2{\pi }^{*}$ transitions from < 0.2 to 2.2 eV for C $1s$ and from 1.15 to 3.5 eV for O $1s$. Shifts of 0.3 eV (for C $1s$) and 1.7 eV (for O $1s$) towards lower energy are resolved for the first time and are explained in terms of the electronic distribution in excited CO.