Tilted CO on clean and potassium-covered Ni(110): Adsorbate orientation from polar-angle x-ray-photoelectron diffraction

Carbon monoxide adsorbed on clean and K-covered Ni(110) surfaces is studied by polar-angle x-ray-photoelectron diffraction to determine the C-O bond orientation relative to the surface normal. At 300 K CO adsorbs perpendicularly on clean Ni(110) with the C down, while at 120 K a high-coverage layer forms with CO tilted ±{}21^∘{} from normal in the [001] azimuth. The coadsorbed K/CO layer at 300 K is a mixture of tilted and perpendicular CO, the former having a tilt angle of 32^∘{} in [001] azimuth. This tilted CO is due to the K interaction and is more strongly absorbed than perpendicular CO.