The advantage of the application of x-ray absorption spectroscopy

X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), is a type of absorption spectroscopy that indicates the feature in the X-ray absorption Spectra (XAS) of condensed matter due to the photo absorption cross section for electronic transitions form an atomic core level to final state in the energy region 50-100 ev above the selected atomic core level ionization energy. The K edge x-ray absorption spectrum of most elements of the periodic table can be performed through full multiple scattering calculations. Then, on the basis of a linear combination of the XANES spectra of reference compounds, the presence of the different phases present inside the materials can be quantified. Here, we show that for nanometer scale metallic clusters, it is not sufficient to consider only the electronic state of the metal of interest to perform a linear combination analysis. In the case of these peculiar materials, special attention has to be paid to different structural parameters, for example, the size and morphology of the cluster, the interatomic distance (taking into account contraction/dilatation processes), and the presence of hetero metallic bonds (in the case of bimetallic clusters). Moreover, this approach is not specific to the metallic state. As a conclusion, the quantitative measurement of the structural parameters coming from EXAFS analysis constitutes an invaluable starting point for the FEFF-PCA simulation. The advantages and limitations of the methods are discussed. Recent advances in extended EXAFS and polarized EXAFS using oriented membranes and single crystals are explained. Developments in theory in understanding the XANES spectra are described. The application of X -ray absorption spectroscopy to the study of the Mn4Ca cluster in Photosystem II is presented.