Spatial distribution of photoelectrons participating in formation of x-ray absorption spectra

Interpretation of x-ray absorption near-edge structure (XANES) experiments is often done via analyzing the role of particular atoms in the formation of specific peaks in the calculated spectrum. Typically, this is achieved by calculating the spectrum for a series of trial structures where various atoms are moved and/or removed. A more quantitative approach is presented here, based on comparing the probabilities that a XANES photoelectron of a given energy can be found near particular atoms. Such a photoelectron probability density can be consistently defined as a sum over squares of wave functions which describe participating photoelectron diffraction processes, weighted by their normalized cross sections. A fine structure in the energy dependence of these probabilities can be extracted and compared to XANES spectrum. As an illustration of this novel technique, we analyze the photoelectron probability density at the Ti K pre-edge of TiS2 and at the Ti K-edge of rutile TiO2.Comment: Journal abstract available on-line at http://link.aps.org/abstract/PRB/v65/e20511

Determination of Local Structure of Molecules Adsorbed on Solid Surfaces by XANES

A method of inverse problem solution in the many-centre shape resonance theory is applied to study adsorption states of molecules on solid surfaces. The main idea is to the effect that positions and widths of maxima in XANES related to quasi-stationary one-electron states (shape resonances) depend considerably on local geometry of molecules. The oxygen K spectra of physisorbed and chemisorbed O2 on Cu(100) were investigated. An adsorptive complex was simulated by clusters containing up to eight atoms. It was found that the chemisorbed molecule location is on the Cu atom, the Cu-O distance is 2.01 Å and the changed O-O distance is 1.38 Å

Determination of Muffin-Tin Potential by XANES

A scheme of the MT-potential construction by using experimental data is proposed. It is based on the inverse problem solution in the theory of many-centre shape resonances. Input data are positions Ei and widths Γi of maxima in XANES corresponding to shape resonances. The MT potential within atomic spheres is considered in the form Vat(r)+∑n an rn where Vat is a given atomic potential, and the coefficients an are chosen so that calculated and experimental characteristics of resonances are close at most