Azimuthal Anisotropy in Deep Core-Level X-Ray Photoemission from an Adsorbed Atom: Oxygen on Copper(001)

For oxygen adsorbed on a Cu(001) surface, the O $1s$ x-ray photoelectron intensity is found to exhibit a complex azimuthal anisotropy with an overall amplitude of ∼ 26% for a grazing 10° angle of emission. No significant anisotropy is observed at 45°. Several reasons for expecting a direct relationship between such final-state scattering effects and atomic geometry are discussed, and the data are found to be suggestive of a surface-chemisorbed $c(2\mathrm{}\times 2)$ oxygen overlayer in fourfold coordination.