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Abstract:
We report results of an angle resolved photoelectron spectroscopy (ARUPS) study using synchrotron radiation from the BESSY storage ring of the CO + O (2×1)/Pd(111) coadsorbate system in comparison with the CO(√3 × √3)R30°/Pd(111) adsorbate. The band structures of the CO induced 5σ1π and 4σ levels for both structures are observed and favourably compared with the proposed structure models as well as tight-binding model calculations. Light polarization dependent measurements as well as the angle dependence of the 4σ shape resonance indicate that the CO molecular axis in the pure CO adsorbate is perpendicular to the Pd(111) surface, while it appears slightly (<10°) inclined with respect to the surface normal in the coadsorbate. We show by comparison with other pure CO adsorbates using the measured E versus k‖ dispersions that the 4σ wave function in the coadsorbate is very similar to the pure adsorbate. It is shown that this is different with respect to other, namely CO + K, coadsorbates.
