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.
Applications of Synchrotron Radiation
Following a brief review of its properties, discussions are presented of the application of synchrotron radiation to: (a) the determination of atomic arrangements using extended x-ray absorption fine structure (EXAFS); (b) the determination of atomic arrangements using x-ray anomalous scattering; (c) dynamic small angle x-ray scattering; (d) x-ray lithography and microscopy; (e) the determination of surface electronic states using vacuum ultraviolet radiation; (f) time resolved fluorescence from protein molecules.
LIII-Edge Anomalous X-ray Scattering by Cesium Measured with Synchrotron Radiation
Diffraction of monochromatized synchrotron radiation by crystals of cesium hydrogen tartrate has been used to measure the magnitude and phase of x-ray scattering for cesium near the LIII absorption edge. In this wavelength region the scattering amplitude of cesium is reduced by as much as 25 electrons per atom, compared to scattering of copper Kα x-rays. This change, which varies as a function of wavelength, affects the diffraction intensities in a manner similar to isomorphous substitution, and it is large enough to have promise for phase determination in the study of macromolecular structures. This experiment also demonstrates that accurate diffractometer measurements are possible with synchrotron radiation produced by an electron storage ring.