Adsorption Site Determination by Means of Surface Core Level Shift High Energy Photoelectron Diffraction:Pd{110}(2×1)p2mg−CO

We propose a novel application of the photoelectron diffraction method for determining the adsorption site of an adsorbate, based on the diffraction of high kinetic energy photoelectrons originating from the topmost layer of the substrate. Sensitivity to the topmost layer is achieved by working at grazing emission angle and by means of the adsorbate induced surface core level shift. A simple single scattering theory is shown to be adequate to interpret the data. We apply the method to the $\mathrm{Pd}\mathrm{}\left\{110\right\}(2\mathrm{}\times 1)p2mg-\mathrm{CO}$ system and provide clear evidence that CO adsorbs in the short bridge sites.