Cluster modelling of core electron photoabsorption of CO adsorbed on Cu(100)

Quantum chemical calculations of discrete and continuum near-edge X-ray absorption spectra of carbon monoxide adsorbed on Cu(100) are presented and discussed. The surface is modelled by clusters using one-electron effective core potentials for distant atoms, allowing cluster sizes up to 50 atoms to be treated. The employed theoretical approach, the direct, atomic orbital, static exchange technique, implementing the independent-particle approximation close to the basis set limit, is shown to provide good representations of the near edge X-ray absorption spectra both for free and adsorbed CO. The experimental observations of reduction of energy and intensity of the first pi* resonance and a compression of the discrete part of the spectra are reproduced by the calculations. The origin of these effects is discussed.