Determination of the local structure and parameters of the one-electron potential from XANES data (inverse problem of XANES theory)

A method of obtaining complex information on the structure of polyatomic systems using experimental data for one-electron quasistationary state (shape resonance) is developed. The method involves the equation for S-matrix poles in the muffintin (MT) approximation. The parameters of the model (intemuclear distances, valence angles, and potential characteristics) are fitted in such a way that the S-matrix poles in a complex energy plane be maximally close to {E-iГ/2}, where E and Fare the energies and widths of the XANES maxima of one-electron origin. Testing the method on a number of objects shows that it determines internuclear distances with an accuracy of 1% and valence angles with an accuracy of 3%. Among the potentials of this type, the empirical potentials obtained are the best for describing shape resonances. The suggested scheme is applicable in determining the microstructure and in the cases where the diffraction methods of structural analysis do not work (unordered systems, molecular adsorption on the surface of solids, etc.). Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 6, pp. 1013–1017, November–December, 1998.