Mdssbauer absorption spectroscopy,

Sample purity is a key concern. The NRVS experiment is a bulk technique sampling all Fe nuclei, and impurities that also contain the probe nucleus may confound quantitative data interpretation. Impurities may be introduced during sample preparation or may result from sample instability during measurement. Because of this, care must be taken to ensure purity and reproducibility as judged by Mossbauer (see Mdssbauer Spectroscopy), single-crystal X-ray diffraction, electronic absorption spectroscopy (see Electronic Spectroscopy), Raman spectroscopy or other qnalitative techniqnes. 

Because the synthetic iron oxides whose synthesis is described in this book consist of very small crystals ranging in size from ca. 3 nm to several Lim, they are characterized and checked for purity by the techniques commonly used for submicroscopic to nano-sized particles. The most important of these techniques are X-ray powder diffraction and electron microscopy. In addition, Mdssbauer spectroscopy, infra red absorption spectroscopy and themial analysis provide useful information (Wilson, 1987). 

Since 1980, newer physical techniques such as Mdssbauer spectroscopy, X-ray absorption spectroscopy and iron-sulfur-core extrusion have been used to address the question of the structure of FeS-X. The initial Mossbauer spectroscopic study by (EH) Evans, Rush, Johnson and (MC W) Evans2o indicated... 

Abstract Structural and spectroscopic data when combined with theoretical calculations provide adequate descriptions of the electronic structures of the nitrosyl moiety in nitric oxide(II) complexes. This concise overview discusses the spectroscopic features of metal nitrosylates. The results of IR, Raman, UV-Vis, EPR, Mdssbauer, magnetic circular dichroism, NRVS, X-ray absorption spectroscopy, and other methods are reviewed and spectroscopy-based conclusions concerning the structure and reactivities of nitrosyls are summarized. 

K. E. R. England, C. M. B. Henderson, J. Chamock, and D. J. Vaughan, "Investigation of Fe Structural Environments in Leucite Type Framework Silicates Using a Combination of Mdssbauer and X-ray Absorption Spectroscopies," Hyperfme Interact., 91,709-14 (1994). 

Fig. 2.44. Mossbauer spectroscopy (a) nuclear transitions giving rise to the Mossbauer effect in Fe (b) principles involved in the Mossbauer spectrometer (c) Mdssbauer resonant absorption of iron in different crystal environments and the resulting spectral types. (After Vaughan and Craig, 1978 reproduced with the publisher s permission).

The conclusion that the cobalt and iron complexes 2.182 and 2.183 are formally TT-radical species is supported by a wealth of spectroscopic evidence. For instance, the H NMR spectrum of the cobalt complex 2.182 indicated the presence of a paramagnetic system with resonances that are consistent with the proposed cobalt(III) formulation (as opposed to a low-spin, paramagnetic cobalt(IV) corrole). Further, the UV-vis absorption spectrum recorded for complex 2.182 was found to be remarkably similar to those of porphyrin 7r-radicals. In the case of the iron complex 2.183, Mdssbauer spectroscopy was used to confirm the assignment of the complex as having a formally tetravalent metal and a vr-radical carbon skeleton. Here, measurements at 120 K revealed that the formal removal of one electron from the neutral species 2.177 had very little effect on the Mdssbauer spectrum. This was interpreted as an indication that oxidation had occurred at the corrole ligand, and not at the metal center. Had metal oxidation occurred, more dramatic differences in the Mdssbauer spectrum would have been observed. 

The Mossbauer effect is the emission and resonant absorption of nuclear y-rays studied under conditions such that the nuclei have negligible recoil velocities when y-rays are emitted or absorbed. This is only achieved by working with solid samples in which the nuclei are held rigidly in a crystal lattice. The energy, and thus the frequency of the y-radiation involved, corresponds to the transition between the ground state and the short-lived excited state of the nuclide concerned. Table 2.4 lists properties of several nuclei which can be observed using Mdssbauer spectroscopy. 

Doyle CS, Traina SJ, Ruppert H, Kandelewicz T, Rehr JJ, Brown GE Jr (1999) XANES studies at the A1 X-edge of aluminum-rich surface phases in the soil environment. J Synchrotron Rad 6 621-623 Drager G, Frahm R, Materlik G, Briimmer O (1988) On the multiplet character of the X-ray transitions in the pre-edge stmcture of Fe K absorption spectra. Phys Status Solidi 146 287-294 Drits VA, Dainyak LG, Muller F, Besson G, Manceau A (1997) Isomorphous cation distribution in celadonites, glauconites and Fe-illites determined by infrared, Mdssbauer and EXAFS spectroscopies. Clay Minerals 32 153-179... 

Proper understanding of the process of DCL in the presence of catalysts needs an understanding of the electronic changes a catalyst goes through during a DCL process. Huffman et al. have reviewed the use of Mdssbauer spectroscopy, magnetization, and x-ray absorption studies to determine the chemical status of the iron-based catalysts before... 

Studies on concentrated lanthanide metallic systems have also made it possible to establish a correlation between nonintegral valence (observable in concentrated lanthanide systems through lattice constant, Mdssbauer isomer shift, soft X-ray absorption and X-ray photoemission spectroscopy measurements) and nonmagnetic behavior of a lanthanide ion below the characteristic temperature. This has led to the concept of valence fluctuations (or interconfiguration fluctuations) which has stimulated the current intense activity among theorists and experimentalists alike. 

The nucleus of an isotope suitable for Mdssbauer spectroscopy must have an excited state of moderately low energy (less than about 200 keV) to permit the occurrence of recoilless emission and absorption, and the excited state must be accessible, preferably by the spontaneous decay of a parent isotope with a... 

Stoichiometric iron molybdate (Fe2(Mo04) ) was prepared by coprec itation from aqueous solutions of iron (III) nitrate and ammonium heptamolybdate it was characterised BET analysis, XRD, atomic absorption spectrophotometiy, XPS, EDX, SEM, FTIR and Mdssbauer spectroscopy. Surfece acidity was characteri by NH3 TPD (temperature programmed desorption). 

Spectroscopic methods for hydration of ions were reviewed for structural aspects and dynamic aspects of ionic hydration by Ohtaki and Radnai (150). They discussed X-ray diffraction, neutron diffraction, electron diffraction, small-angle X-ray (SAXS) and neutron-scattering (SANS), quasi-elastic neutron-scattering (QENS) methods, extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge structure (XANES) spectroscopies, nuclear magnetic resonance (NMR), Mdssbauer, infrared (IR), Raman, and Raleigh-Brillouin spectroscopies. The clay interlayer molecular modeling where clay surface is interfaced with aqueous solution also includes ions that are also solvated by interlayer water. 

For selected elements, the electronic simation of atoms, typically characterized as formal oxidation states, can often be determined directly by several methods, including Mdssbauer spectroscopy. Relative energies of orbitals, occupied or vacant, and ionization energies, can be measured by methods such as UV/visible spectroscopy, photo-electron spectroscopy (including X-ray methods for core orbitals) and X-ray absorption... 

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