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(2×2) oxygen overlayer in fourfold coordination.