Local Order at the Manganese Sites in Ionic Solutions by XANES (X-ray absorption near edge structure)

The idea that important geometrical informations about local structure are contained in XANES spectra has stimulated theoretical and experimental studies in this field(1,4). The low energy part of the x-ray absorption spectra, in fact, is sensitive to the geometrical arrangement of the environment around the absorbing atom because of the strong scattering power of these low energy photoelectrons, favoring multiple scattering (MS) processes. Going to the high energy region of the spectra a gradual turn-over occurs from the MS regime to the single scattering (SS) regime where the modulation in the absorbtion coefficient (EXAFS) is substantially due to the interference effect of the outgoing photoelectron wave from the absorbing atom and the backscattered wave from each surrounding atom (5,6). Hence, while this part of the spectrum provides information about the pair correlation function, the first one contains information about higher order distribution functions by MS pathways which begin and end at the absorbing atom.