Anomalous C-O Bond Weakening of Side-On-Bonded Carbon Monoxide on a Potassium-Promoted Ru(001) Surface

The coadsorption of low coverages of CO and potassium (${\theta }_{\mathrm{K}}<0.10\mathrm{}$) on Ru(001) is characterized by a single adsorption state with a C-O stretching frequency of ∼ 1460 ${\mathrm{cm}}^{-1\mathrm{}}$. Vibrational overtone spectroscopy and isotopic scrambling in thermal desorption reveal anomalously weak C-O bonds. Comparisons with metal carbonyls, molecularly adsorbed acetone, and oxygen on transition metals suggest a side-on-bonded molecule with its molecular axis parallel to or inclined towards the metal surface.