Electronic structures XANES spectra

X-ray absorption near edge structure (XANES) The X-ray absorption spectrum, as for EXAFS, may also show detailed structure below the absorption edge. This arises from excitation of core electrons to high level vacant orbitals, and can be used to estimate the oxidation state of the metal ion. 

In solid state physics, the sensitivity of the EELS spectrum to the density of unoccupied states, reflected in the near-edge fine structure, makes it possible to study bonding, local coordination and local electronic properties of materials. One recent trend in ATEM is to compare ELNES data quantitatively with the results of band structure calculations. Furthermore, the ELNES data can directly be compared to X-ray absorption near edge structures (XANES) or to data obtained with other spectroscopic techniques. However, TEM offers by far the highest spatial resolution in the study of the densities of states (DOS). 

Despite the overall similarity between the XANES spectrum of the mixed model compounds and the asphaltene and coal samples, there are some significant differences in the relative energies of the various features. One possible explanation for these differences is that subtle electronic differences at the sulfur are reflected in the sulfur XANES. Such differences might be expected to arise from extended ring structures or from substituents. This will be a subject for further study. 

It is well known that the fine structure of the K absorption edge arises fiom the photoelectric effect of a Is orbital electron of an absorption atom. It is obvious that the peaks in the rising part on XANES spectra are ascribed to the electron transition fiom an inner shell orbital to higher molecular orbitals (called as Is electron transition in this rqrort). Therefore, to estimate the probabilities of the Is electron transition by an electronic dipole theory, theoretical XANES spectrum can be caloilated using molecular orbital calculations. ... 

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