Unusual C-O Bond Weakening on a Clean Metal Surface: CO on Cr(110)

Abstract

A unique CO chemisorption mode (${\ensuremath{\alpha}}_{1}\mathrm{CO}$), with the lowest reported CO stretching frequencies (1150-1330 ${\mathrm{cm}}^{\ensuremath{-}1}$) on any clean or promoted metal surface, has been identified on Cr(110) by means of EELS, ESDIAD, LEED, AES, and oxygen coadsorption experiments. A "lying down" binding configuration in twofold-symmetric hollow sites is proposed for ${\ensuremath{\alpha}}_{1}\mathrm{CO}$ molecules. For ${\ensuremath{\theta}}_{\mathrm{CO}}>0.25$, a second mode (${\ensuremath{\alpha}}_{2}\mathrm{CO}$) bound perpendicular to Cr(110) is populated.