Absorption edge position

The features of a XANES spectrum that are typically used to determine the average oxidation state of an element are the absorption edge position... 

The position of an edge denotes the ionization threshold of the absorbing atom. The inflection in the initial absorption rise marks the energy value of the onset of allowed energy levels for the ejected inner electron (216). For a metal this represents the transition of an inner electron into the first empty level of the Fermi distribution (242) and in case of a compound the transition of an inner electron to the first available unoccupied outer level of proper symmetry. Chemical shifts in the absorption-edge position due to chemical combination (reflecting the initial density of states) were first observed by Bergergren (27). 

X-Ray Absorption-Edge Positions, Edge Shift, First-Shell Radii (Corrected), and Related Data for Mn02-Si02 Catalyst Sample and Reference Materials... 

The formation of Ti-O-Ti bonds contributed to the slight delocalisation of the absorption edge positions towards higher wavelengths with increasing titania loading [1,5,17], but no specific absorption due to crystalline TiOi was detected at 330 nm [17,18] (Fig. 3). However, both bulk titania and the mechanical mixture sanqile (mix-TiSi) showed identical UV-Vis DRS patterns of Ti in octahedral sites [5], as seen in Fig. 3 (a) and (b), respectively. 

Anomalous dispersion studies absorption edge position and magnitude of white line as a function of metal atom oxidation state... 

Figure 8. Optical absorption (solid curves), PL (dotted curves), and PLE (dashed curves) spectra of the PA-terminated Si nanocrystals Average diameters obtained from TEM observations are 2.4 nm for spectrum (a) and less than 1.5 nm for spectra (b) and (c). We are unable to clearly identify the nanocrystals smaller than 1.5 nm due to the insufficient contrast between the nanocrystals and the background amorphous carbon film. Sample (c) was prepared by ultrasonically irradiating sample (b) in DI water for 5 h. Gray and black arrows indicate the PL peak and absorption edge positions, respectively.

The relationship between the empirically determined edge position to the energy of the orbitals at the metal centre is also often unclear. While the absorption edge position is sometimes considered to represent the energy of the vacuum level (the position of Eo which is the onset of the continuum), this seems by no means general. In cases where the absorption edge energy can be compared to the ionisation potential as measured by x.p.s., then... 

Mo) ions have indicated that the onset of the continuum is at the base of the metal K-absorption edges, and therefore at a lower energy than the normal definition of the edge position.Clearly care must be taken in considerations of absorption edge positions, but in some cases they may provide an indication of oxidation... 

The following comments can be made about the shifts of the K and L absorption edges of aluminum. Our calculations predict that the contribution of the shift of the inner levels should be about 1.5 eV in both cases. This value disagrees with the experimental data because of the indeterminacy of the absorption edge positions and because of some underestimation of the shifts of the K and L levels. Moreover, our description of the changes in the electronic structure of aluminum, based on the assumption that the outer electrons are displaced away from aluminum... 

X-ray absorption near-edge structure (XANES) can be used to analyze the oxidation states of many elements and to quantify the components of different valences for a given element in the samples. In order to perform the analysis of oxidation state, we can obtain the information by comparing the absorption edge position of the absorbing atom with that of standard samples. Moreover, we can use linear combination XANES (LC-XANES) to quantify and determine oxidation states of a given element in the samples. ... 

XANES spectra to measure the oxidation states of Au atom absorbed on the surface of materials. As a result, they proved that Au(III) ions adsorbed both on Ti02 and AI2O3 were reduced to Au(0) in the terms of Au/Ti02 and Au/ AI2O3 nanoparticles smaller than 1 nm. The Au(III) and Au(0) foil have different absorption edge positions as characteristics, while Au(0) foil and Au coated nanoparticles have an absorption edge position in common considered as the same covalence state (Figure 11.2). 

Spectra of Cco gGdo lOi 95 sintered under air are comprised of charge transfer bands (Fig. 66). The increase of sintering temperature improves spectra resolution without any shift of the absorption edge position. 

For As, Mo, and Se all samples displayed well-defined absorption edges, identified by the sharp increase in absorption over a 10 eV interval. The position of the absorption edge is sensitive to the oxidation state of the absorbing atom and thus has been used to determine the oxidation state of As, Mo, and Se in the mine tailings. 

Position assessed by method of Iwata, et al., reference 83. Mobility assessed by comparisons of anomalous Fe peak heights data collected at or near the iron K absorption edge. (See references 84 and 88.) ... 

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