Edge spectra

There are, however, differences of opinion regarding the justification of using these K-shell, absorption-edge spectra for assignments to specific oxidation-states (H36). Both symmetry and ligands can affect absorptions by as much as 10 eV, and the absence or presence of a center of symmetry can determine whether a given transition is forbidden or... 

Mansour, A. N., Cook, J. W., and Sayers, D. E., "Quantitative Technique for Determination of the Number of Unoccupied d Electron States In a Pt Catalyst from the L X-ray Absorption Edge Spectra," J. Chem. Phys. (to be published). 

Figure 5. Lji edge spectra of Ru dispersed on undoped, Zn -and w6+-doped Ti02...

The K-edge spectra of [Ni(287)2]2 and [Ni(cdt)2]2 are remarkably similar to each other and to those of natural hydrogenases.196 Some complexes with ligand (289) (R = NMe2, R = H, Me, NMe2) have been characterized using electronic and near infrared spectroscopy.823 Complex [Ni(289)2]2 served to study phase transformation behavior by microscopy and DSC.824... 

Figure 21. Near-edge spectra for (A) copper upd monolayer on a gold (111) electrode surface and (B) after electrochemi-cally stripping the copper monolayer.

Another example of the potential utility of polarized edge spectra for structure determination is found for [MoO J2" (28). This molecule has C2V symmetry and the C2 axes of all of the molecules in the unit cell are collinear. Thus, when the crystal is oriented with the polarization parallel to the S-S interatomic vector, the polarization is perpendicular to the Mo-0 bonds and nearly parallel to the Mo-S bonds. Similarly, the crystal can be oriented with the polarization perpendicular to the Mo-S bonds and nearly parallel to the Mo-0 bonds. For both orientations, excellent agreement was obtained with SCF-X a calculations of the edge structure (j ). 

The Fe K-edge spectra were recorded in the transmission mode and a metallic iron foil spectrum was measured simultaneously with each sample spectrum for energy calibration. X-ray absorption spectra for each sample were collected from 7,520 to 8,470 eV, with a step size of 0.40 eV and acquisition times of ca. 68 s per sample. Measuring each sample, in turn, and repeating... 

Similarly, comparison of the Mo K edge absorption spectra for tailings and reference compounds of known oxidation states (Fig. 2), shows that Mo6+ is the dominant form of molybdenum in the mine tailings. The characteristic pre-edge feature in the near edge spectra indicates that Mo in the tailings occurs mostly as a molybdate. 

Least squares fitting of the near edge spectra of the tailings to that of the standard reference spectra is currently underway to establish the chemical... 

Edge dislocations, 19 295-296 Edge spectra, electronic and size effects, 34 274... 

The problems associated with quantitative studies of structure based upon this viewpoint of X ray absorption-edge spectra may be similar to those encountered using electron beams of comparable energy, 3 to 100 ev., to carry out electron diffraction studies of crystal structure. Qualitatively, this analogy can be carried further, as both the X ray spectra and the electron beam diffraction in this energy range are influenced by only the first few atom layers. 

Some references are made in the following survey of spectra to this analogy between diffraction and absorption edge spectra. However, the real purposes of the survey are to provide background for application of these spectra to catalyst problems and to point out the empirical relationships between these spectra and structural chemistry. 

The present survey of absorption edge spectra of known compounds provides a background concerning the type of information these spectra may provide in catalyst studies. Spectra emphasizing the first 30 ev. range... 

Fio. 1. Four distinct types of X-ray absorption edge spectra of manganese in varying chemical states. 

X-edge spectra of cobalt compounds appear quite similar to those of manganese compounds. The ionic cobaltous salts and hydrates produce t3q>e I spectra. In Fig. 9 and 10 the spectra of the salts (except for CoBrj) have their principal maximum at 18-20 ev. Spectra of the cobaltic salts stabilized with a coordination sphere of ammonia or of ethylene diamine, shown in Figs. 11 and 12, are all very similar, are of typo I, and have their... 

Fig. 14. Cobalt K-edge spectra of two mixed oxides compared to spectra of two common cobalt oxides. CoiMn40s is of hausmanite type tetragonal structure, CotO and CoNiMniOi are of cubic spinel structure.

Fio. 15. Manganese K-edge spectra of five mixed oxides, including two whose cobalt edge spectra were included in Fig. 14. Mni04 and CojMniOa are tetragonal others are cubic spinels. 

The first instance of successful application was in the examination of some supported chromia catalysts. A pronounced variation in catalyst performance, caused by certain oxidative pretreatments, was found to correlate with variations in absorption edge spectra. Spectra involved were... 

It should be noted that there has been some confusion In the literature with respect to the apparent oxidation state of the T3 site In different T2D laccase preps. This derives from the use of Indirect methods to define oxidation state. We have run x-ray edge spectra of T2D laccase prepared by four of the research groups strongly Involved In this field, and In all cases the Type 3 site Is found to be fully reduced. 

XANES of Model Compounds. Table I lists the first inflection points of the sulfur K edge spectra for a series of model compounds whose structures are believed to be representative of the types of organically bound sulfur found in heavy petroleum and coals. 

XANES of Petroleum Residua. On the left side of Figure 1 the sulfur K edge spectra for three different petroleum residua and the asphaltene samples prepared from them are shown. While the absorption spectra all appear to be similar, differences are revealed by examining the third derivatives of the spectra, which are shown on the right side of the figure. All the residua samples appear to contain sulfur bound in sulfidic and thiophenic forms, the amount of sulfidic sulfur increasing from sample 1 to sample 3. The asphaltene samples prepared from residua 2 and 3 also appear to contain both forms. Assuming that the composition of the sulfur... 

Mn(III) r Mn(IV) transition, 33 226-227 Mn-K edge spectra, 33 228-229 Oj-evolving complex, 33 221 proton release pattern, 33 235 rebinding, 33 223 spin echo studies, 33 233-234 S state model, 33 221 temperature dependence of EPR signals, 33 231-232... 

Figure 2. Upper-panel Fluorescence-yield near-edge spectra of a NiO/Ni(100) layer measured before and after annealing the surface to 800 K. Lower-panel Simultaneous measurement of the partial electron-yield of the same NiO/Ni(100) surface.

Conradson, S. D Abney, K. D. et al. 2004. Higher order speciation effects on plutonium L3 X-ray absorption near edge spectra. Inorganic Chemistry, 43, 116-131. 

The mixed oxides obtained by hydrolysis at neutral pH of TIOT and TEOS over a wide range of compositions have also been investigated. The X-ray absorption near-edge spectra (XANES) of the mixed oxides having a composition corresponding to Ti Si = 1 8 (Fig. 4) indicate that Tiiv is present not in an octahedral coordination, as in anatase, but instead in a lower coordination, 5- or a mixture of 4-, 5-, and 6-coordination. 

---