Nickel EXAFS spectra

Froment and co-workers have employed reflexafs77 (reflection EXAFS) for studying passive films on iron78 and nickel.79 80 The experiment consists of measuring the ratio of the reflected and incident intensities as a function of energy. Although an EXAFS spectrum can be obtained from such a measurement, the process is somewhat involved since the reflectivity is a complex function... 

Fig. 2. Ni K-edge EXAFS spectrum of urease. The curve (+) is calculated for a single type of nickel site, and the minimization of parameters was based on those for the model complexes Ni(l-n-propyl-2-hydroxybenzylbenzimidazole)3(Cl04) and Ni(2-hydroxy-methylbenzimidazole)3Br2. Atoms (with distances in nanometers given in parentheses) in the simulation were N (0.204), O (0.206), O (0.225), C (0.294), C (0.312), N (0.392), and C (0.394). Reproduced, with permission, from Ref. 34.

Fe(II)C20 2 H O is the only bivalent metallic oxalate whose XRD structure has been solved It is nevertheless isostructural with the Ni(II) and with the Zn(II) analogs. In the nickel derivative for example, the square planar NiO site within the planar ribbons is completed with two axial water ligands. The shortest Ni—Ni intermolecular contribution, computed from X-ray powder diffraction data of Ref. corresponds to 4 Ni at 5.20 A. The room temperature EXAFS spectrum (Fig. 14i, j) present 3 peaks. Peaks 1 and 2 are unambiguously identified as Ni—O and Ni—C contributions. The third peak will be discussed later on. Upon lowering the temperature towards 30 K, these first peaks are almost invariant while new contributions appear at larger distances. Therefore, the three first peaks are certainly due to intramolecular contributions while the temperature dependent contributions probably corresponds to intermolecular Ni—Ni distances. 

Figure 13 shows the calibration curve of phase-lag for the nickel foils of various thickness. This result suggests the possibility of estimating the thickness of plated materials on the metal. Figure 14 shows the PAXAS spectrum of nickel-plated copper. In the photoacoustic amplitude spectrum, EXAFS of copper at the subsurface of sample was still detected clearly. This means that PAXAS method can be applied... 

EXAFS studies (Hasnain and Piggott, 1983 Alagna et al., 1984) have shown that the spectrum of urease is similar to those of benzimidazole complexes (Fig. 5-2) suggesting that the nickel is coordinated by histidine nitrogen and oxygen ligands. 

Nickel tetracarbonyl and nickel complexes with mixed carbonyl and alkylphosphine ligands in zeolite Y have been studied with EXAFS, NMR, and FTIR spectroscopies (85,240-242). The loading of Ni(CO>4 in dehydrated zeolite X can be as high as 28 wt%, corresponding to 2.75 Ni(CO>4 molecules per supercages. The IR spectrum of Ni(CO>4 was found to be affected by the cations inside the zeolite supercages. The spectrum of... 

The usual procedure of the evaluation of an EXAFS data of the XA spectrum involves first the background subtraction and the evaluation of % (Figure 1.4c). Then one has to separate the contribution of the various coordination shells to visualize their data. This is done by a Fourier transform to the distance space. Figure 1.4d clearly shows four well-developed shells of crystalline Ni metal, R to R, which are characteristic of a cubic face-centered metal. This result still needs a correction by the phase shift <1> and the evaluation of Ni and o. This occurs for specific specimens by comparison with EXAFS data of well-characterized standards like nickel metal in this case or by calculation of the EXAFS results with a program like FEFF [12] or data analysis packages from the Internet with reasonable assumptions [13]. For this purpose, the % data of each shell are separated and... 

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