X-Ray absorption spectra of

The electronic spin-state crossover in [Fe(HB(pz)3)2] has also been observed in the fine structure of its fC-edge x-ray absorption spectrum [38]. The changes in the x-ray absorption spectra of [Fe(HB(pz)3)2] are especially apparent between 293 and 450 K at ca. 25 eV, as is shown in Fig. 5. The 293 K x-ray absorption spectral profile observed in Fig. 5 for [Fe(HB(pz)3)2] has been reproduced [39] by a multiple photoelectron scattering calculation, a calculation that indicated that up to 33 atoms at distances of up to 4.19 A are involved in the scattering. As expected, the extended x-ray absorption fine structure reveals [38] no change in the average low-spin iron(II)-nitro-gen bond distance of 1.97 A in [Fe(HB(pz)3)2] upon cooling from 295 to 77 K. 

Our discussion of electronic structure has been in terms of band filling only. Of course, there is a lot more to know about band structures. The density of states represents only a highly simplified representation of the actual electronic structure, which ignores the three-dimensional structure of electron states in the crystal lattice. Angle-dependent photoemission gives information on this property of the electrons. The interested reader is referred to standard books on solid state physics [9,10] and photoemission [16,17]. The interpretation of photoemission and X-ray absorption spectra of catalysis-oriented questions, however, is usually done in terms of the electron density of states only. 

Ftg. 14. Photoacoustic X-ray absorption spectra of (a) signal amplitude and (c) phase, and (b) absorption sptttoim for nickel-plated copper foil (10 pm). Chopping frequency 10 Hz. Ring current 175 to 167 mA... 

Figure 16-18 Mossbauer X-ray absorption spectra of iron-sulfur clusters. (See Chapter 23 for a brief description of the method.) Quadrupole doublets are indicated by brackets and isomer shifts are marked by triangles. (A) [Fe2S2]1+ cluster of the Rieske protein from Pseudomonas mendocina, at temperature T = 200 K. (B) [Fe3S4]1+ state of D. gigas ferre-doxin II, T = 90 K. (C) [Fe3S4]° state of D. gigas ferredoxin II, T = 15 K. (D) [Fe4S4]2+ cluster of E. coli FNR protein, T = 4.2 K. (E) [Fe4S4]1+ cluster of E. coli sulfite reductase, T = 110 K. From Beinert et al.260...

Morgan, Thomas H. 83 Mossbauer X-ray absorption spectra of iron-sulfur clusters 860 Mosses 29... 

The X-ray absorption spectra of a series of 28 model Fem complexes and those of ovatransferrin, protocatechuate 3,4-dioxygenase and catechol 1,2-dioxygenase have been analyzed, and appear to give information on the coordination number of the protein-bound iron. Thus the transferrin complexes appear to be six- or seven-coordinate, while the dioxygenase complexes could be five-or six-coordinate.816... 

Takahasi, O., Yamanouchi, S., Yamamoto, K., and Tabayashi, K. (2006). Theoretical study of the x-ray absorption spectra of small formic acid clusters. Chem. Phys. Letters 419, 501-505. 

Interest in X-ray absorption spectroscopy techniques and particularly in EXAFS, XANES and SEXAFS, has increased enormously since synchrotron radiation facilities were developed at Stanford University 1974. X-ray absorption spectroscopy is a powerful tool in determining the local structure near a particular atom. X-ray absorption spectra of a surface atom can be divided in two parts ... 

Fig. 4.6. Iron K-edge X-ray absorption spectra of K3Fe(CN)6 and IQFe N) showing XANES resonances and EX AES oscillations (Koningsberger and Prins, 1988)...

O. Wessely et al., Dynamical core-hole screening in the x-ray absorption spectra of hydrogenated carbon nanotubes and graphene. Phys. Rev. B 76, 161402 (2007)... 

Fig. 12 Simulated Sc-L2>3 x-ray absorption spectra of trivalent Sc ions (d°) with an initial state admixture of the indicated proportion of a d1 , configuration in the initial state. For details of the calculations, see Ref. [34]...

Fig. 13 Direct comparison of the experimental Sc-L23 x-ray absorption spectra of Sc2 C84 (line+symbols) with a simulation (grey solid line) based upon an atomic multiplet model with an initial state composed of 61% d° and 39% d L configurations. For details,see Ref. [34]...

E. Orgaz, M. Gupta, Theoretical study of the X-ray absorption spectra of Mg2FeH6 ,./. Less-Comm. Met. 130 (1987) 293-299. 

Fine structure of X-ray absorption spectra of heme-containing oxygenases and peroxidases 91MI16. 

Time-resolved X-ray absorption spectra of an activated H5[PV2Moio04o] oxidation catalyst were recorded to determine correlations between the dynamic structure and the catalytic selectivity of the material (Ressler and Timpe, 2007). In addition to experiments carried out under steady-state conditions, time-resolved XAFS measurements at the Mo K-edge were performed under changing reaction conditions (with a time resolution of 30 s per spectrum) (Figure 52). Therefore, the gas-phase composition was isothermally switched from a reducing atmosphere (propene) to an... 

Another important application of selective extra absorption is the use of chemical shifts in the various X-ray emission channels. This opportunity yields the possibility of measuring the valence-selective X-ray absorption spectra, both XANES and EXAFS. This technique has been applied successfully to Fe(III) as a test case (Glatzel et al., 2002). At least in principle, many applications of this methodology are possible. A metal will have a different X-ray emission spectrum than an oxide. This difference can be used to measure the X-ray absorption spectra of the metal and the oxide in a mixed metal oxide. Such mixtures are encountered frequently in heterogeneous catalysis. 

On the other hand, the I(M.4d) show a very complicated behaviour. The configuration 4d94fexcited states of X-ray absorption spectra of metallic lanthanides (102) or M(III) compounds with groundstates belonging to 4/ 1 It is known to contain 10 times as many orthogonal states as /a having in spherical symmetry... 

According to Grunes (107) and others (181,303), single-particle band-structure calculations (206) using the final-state potential with neglect of the core hole do well in predicting the observed X-ray absorption spectral features of metals past threshold (200 eV), which reflect the unfilled p density of states. The present insight is that the final-state rule (181,303) for the calculation of X-ray absorption spectra of metals is satisfactory (72). 

Kutzler, F. W., C. R. Natoli, D. K. Misemer, S. Doniach, and K. O. Hodgson (1980). Use of one electron theory for the interpretation of near edge structure of K-shell x-ray absorption spectra of metal complexes. J. Chem. Phys. 73, 3274-88. 

The X-ray absorption spectra of calcium-containing coals and reference compounds discussed in this paper were recorded at the Stanford Synchrotron Radiation Laboratory during a dedicated run of the Stanford Positron-Electron Acceleration Ring at an electron energy of 3.0 GeV. The calcium K-edge occurs at 4038 eV and data were collected from 3800 to 5000 eV, using a double Si (111) monochromator and a fluorescence detector similar to that of Stern and Heald (16). A more detailed discussion of this work is given elsewhere (17). 

Figure 24. A1 K-edge X-ray absorption spectra of NaY (solid line), HY (dotted line), H-CaY (dashed line) and H-LaY (dot-dash line). Reproduced with permission from reference 63.

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