Spectroscopic link between adsorption site occupation and local surface chemical reactivity.
In this Letter we show that sequences of adsorbate-induced shifts of surface core level (SCL) x-ray photoelectron spectra contain profound information on surface changes of electronic structure and reactivity. Energy shifts and intensity changes of time-lapsed spectral components follow simple rules, from which adsorption sites are directly determined. Theoretical calculations rationalize the results for transition metal surfaces in terms of the energy shift of the d-band center of mass and this proves that adsorbate-induced SCL shifts provide a spectroscopic measure of local surface reactivity.
Core level shifts of undercoordinated Pt atoms.
We present the results of high-energy resolution core level photoelectron spectroscopy experiments paralleled by density functional theory calculations to investigate the electronic structure of highly undercoordinated Pt atoms adsorbed on Pt(111) and its correlation with chemical activity. Pt4f(7/2) core level binding energies corresponding to atoms in different configurations are shown to be very sensitive not only to the local atomic coordination number but also to the interatomic bond lengths. Our results are rationalized by introducing an indicator, the effective coordination, which includes both contributions. The calculated energy center of the valence 5d-band density of states, which is a well known depicter of the surface chemical reactivity, shows a noteworthy correlation with the Pt4f(7/2) core level shifts and with the effective coordination.
POINT SCATTERING THEORY OF X-RAY K-ABSORPTION FINE STRUCTURE,
Abstract : The extended x-ray absorption fine structure is calculated by treating the ejected photoelectron as a spherical wave which expands in the lattice and is partially scattered by neighbors of the absorbing atom. The neighboring atoms are treated as point scatterers and the total scattered wave is summed from the waves scattered by each atom. The fine structure is determined from the dipole transition matrix between the initial K-state and the final photoelectron state. Calculations compare favorably with experimental data. (Author)