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The atom and symmetry specific properties of x-ray emission spectroscopy have been applied to the investigation of CO adsorbed on Ni(100) and Cu(100) surfaces. In comparison to ab initio electronic structure calculations, obtained in density functional theory, we develop a consistent electronic structure model of CO adsorption on transition and noble metals and extend to a conceptual model of the surface chemical bond. A strong CO–substrate interaction is found, characterized by significant hybridization of the initial CO orbitals and the metal bands. In the π system an allylic configuration is found as the result of orbital mixing between the CO 1π, 2π* and the metal dπ-band which is manifested experimentally in the observation of an oxygen lone-pair state. In the σ system experimental evidence of equally strong orbital mixing has been found. Energetically, the adsorbate–substrate complex is stabilized by the π-interaction but is destabilized by the σ-interaction. Furthermore, the internal C–O bond carried by the π-interaction is weakened upon adsorption, which is opposite for the internal C–O σ bond that is strengthened. The equilibrium properties of CO adsorbed on these metals are found to be the direct result of the balance between the σ- and π-interactions; both in terms of the total energy and the local bond properties.

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The physical and electronic structure of the dispersed and (2ϫ2) phases of K/graphite have been characterized by valence and core-level photoemission. Charge transfer from K to graphite is found to occur at all coverages, and includes transfer of charge to the second graphite layer. A rigid band description is reasonably successful in describing important aspects of the data, and our results are consistent with a shift of approximately 0.4 eV in the surface graphite layer for both phases. The C 1s line shape and binding-energy shift as a function of charge transfer can be understood qualitatively by taking into account rigid band effects and the effects of a core hole on the density of states. For the ͑2ϫ2͒ phase the metallic overlayer contributes extrinsic satellites to the C 1s line shape. The K 3p spectrum is strongly affected by the overlayer phase, and in addition indicates very little variation in the substrate charge distribution as a function of coverage in the dispersed phase. The lack of an interface K 3p binding-energy shift for a K bilayer or multilayer is ascribed to a weak K-graphite bond for metallic overlayers. The results have implications for the interpretation of photoelectron spectra of alkali graphite intercalation compounds ͑GIC's͒. ͓S0163-1829͑99͒09111-0͔

High resolution x-ray emission spectroscopy is shown to reveal unprecedented details of the chemical bond formed between a molecule and a transition metal surface. An atom and symmetry projected view of the bonding orbitals is obtained. We find that all outer and inner valence orbitals of the molecule change due to the surface interaction. New types of molecular states are observed which are a direct signature of the surface chemical bond. [S0031-9007(97)