Extended X-ray absorption fine structure EXAFS region

For theoretical as well as for practical purposes, a XAS spectrum is normally divided in two regions (1) the X-ray absorption near-edge structure (XANES) region, and (2) the extended X-ray absorption fine structure (EXAFS) region. 

FIGURE 7.14 X-ray absorption spectroscopy (XAS) spectrum of arsenate with the x-ray absorption near-edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) regions indicated. (Reprinted from Luo, L., and S. Zhang, Sci. China Chem. 53, 12, 2529-2538, 2010. With permission from Science China Press.)... 

Concurrently with the X-ray crystallographic studies, extended X-ray absorption fine structure (EXAFS) studies confirmed many of the bond distances proposed for nitrogenase s FeMoco cluster. The EXAFS data of reference 25 indicate short Fe-Fe distances of 2.61, 2.58, and 2.54 A for M+, M (resting state), and M forms, respectively. The authors believe that the short M center bond lengths indicate Fe-Fe bonds in this cluster. In another study using dithionite-reduced MoFe-protein Fe-S, Fe-Fe, Fe-Mo distances of 2.32, 2.64, and 2.73 A, respectively, were found in the 1 to 3 A region and Fe-Fe, Fe-S and Fe-Fe distances of 3.8, 4.3, and 4.7 A, respectively, were found in the 3 to 5 A region.30... 

X-ray absorption spectroscopy is a powerful tool for nanoparticle analysis due to its selectivity and independence of sample physical state. It is limited in range to the region within about 0.5-0.7 nm of a particular (chosen) absorber atom in the structure, but can be applied to amorphous or even liquid samples. The basic theory behind the origins and analysis of the extended X-ray absorption fine structure (EXAFS) has been well described by Sayers et al. (1970, 1971) and Lee et al. (1981). with mineralogical applications detailed by Brown et al. (1988). The crucial aspect of the EXAFS spectrum is that it is formed by an electron backscattering process in the vicinity of the absorber... 

A variety of experimental techniques have been used to investigate IL structures. Neutron diffraction, X-ray scattering, extended X-ray absorption fine structure (EXAFS) [97-105], and theoretical methods [64, 106-111] are probably the most powerful approaches to quantify IL structure and interactions. For example, X-ray diffraction and absorption studies along with computer simulations have shown that ILs are by no means molecular liquids [64, 89,94,112,113], Unlike a conventional solvent like hexane or chloroform, ILs contain a large number of internal interfaces and exhibit different degrees of order [89, 114], ILs can form liquid crystals, extended hydrogen-bonded networks, inclusion compounds, or microphase separated structures, where polar and non-polar regions are separated by a complex interface [86, 89, 114],... 

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