Orientation of adsorbed CO on Pt(111) + K by x-ray photoelectron diffraction

The structural orientation of CO adsorbed on clean and K-covered Pt(111) was studied by angle-resolved x-ray photoemission of the C 1s, O 1s, and K 2p core-level peaks. The ratio of C 1s to O 1s intensities versus polar angle θ shows a peak near normal emission with a half-width of 24^∘{}-29^∘{}. This peak is due to the forward scattering of C 1s photoelectrons and indicates vertically bound CO ( 10^∘{} tilt) in all cases. The K 2p emission is quasi-isotropic in θ such that CO should be adsorbed on the Pt(111) surface rather than on top of the K species.