Fe spectra

The derivation of the expressions (3.3)-(3.6) is found in Appendix A (cf. CD-ROM). Since for most Fe-spectra the level of nonresonant background counts, Ab, may be in the range of 10-30% of the total counts, the absorber thickness is usually best adjusted to a value between the limits given above. The maximum of SNR( ) is naturally rather broad, such that deviations from / opt of even dz50% are fairly immaterial. 

The previous chapters are exclusively devoted to the measurements and interpretation of Fe spectra of various iron-containing systems. Iron is, by far, the most extensively explored element in the field of chemistry compared with all other Mdssbauer-active elements because the Mossbauer effect of Fe is very easy to observe and the spectra are, in general, well resolved and they reflect important information about bonding and structural properties. Besides iron, there are a good number of other transition metals suitable for Mossbauer spectroscopy which is, however, less extensively studied because of technical and/or spectral resolution problems. In recent years, many of these difficulties have been overcome, and we shall see in the following sections a good deal of successful Mossbauer spectroscopy that has been performed on compounds of... 

The Mossbauer Fe spectra of the films represent the singlet with isomeric shift 5 = +0.20 mm/s and very weak splitting (Fig. 2). This can be probably due to relaxation processes in the nanosized Fe particles. The dimensions of the superparamagnetic iron particles can be estimated to be 30-50 nm. 

In many of the observed spectra referred to in later chapters, it is not possible to use one of the simplifications described above. Solutions are not obtained analytically but by full mathematical analysis using a digital computer. A method of computing the spectrum appropriate to any given symmetry has been given by Gabriel et al. [26, 27]. Similar texts have been specifically directed to the solution of Fe spectra [28-30]. 

Figure 13.23. (a) Fluorescence (F) and absorption (Abs) or fluorescence excitation (FE) spectra of ailT thin films on quartz glass. Excitation in the maximum of absorption band A. angle of incidence 60°. 

Micro-XANES were obtained for Cu and Mn on the same beamline with the same experimental set-up as for the XRF The Fe spectra were collected as a single scan in fluorescence yield mode at selected points within the cross-section... 

Fig, 2a shows the amplitude of triplet and Q. Fe spectra as a function of time. The Q. Fe signal decreased with a t of 1 hr 20 min the triplet signal increased with similar time dependence. Omitting benzyl viologen resulted in a marked increase in tj. ... 

Fig. 5.5. Temperature and gas environment dependence of the Mossbauer spectra for a NiO Co source with a room temperature sodium fenocyanide absorber. The left-hand set of spectra were obtained in a pure oxygen environment and the sets of spectra to the right were obtained with decreasing partial pressures of oxygen. The dashed lines are approximate representations of the temperature dependence for Fe and Fe spectra. (Song Mullen, 1976.)...

Figure 40. (a) Ruoiescence (F) and absorption (Abs) or fluorescence excitation (FE) spectra of a-nT thin films on quartz glass. Excitation in the maximum of absorption band A, angle of incidence 60°. (b) UV-Vis transition energies vs. reciprocal chain-length for the fluorescence peaks and the first absorption peak of o-nT thin films. The lower index A indicates room temperature spectra, the lower index B spectra taken at 77 [181]. 

Woodruff and co-workers introduced the expert system PAIRS [67], a program that is able to analyze IR spectra in the same manner as a spectroscopist would. Chalmers and co-workers [68] used an approach for automated interpretation of Fourier Transform Raman spectra of complex polymers. Andreev and Argirov developed the expert system EXPIRS [69] for the interpretation of IR spectra. EXPIRS provides a hierarchical organization of the characteristic groups that are recognized by peak detection in discrete ames. Penchev et al. [70] recently introduced a computer system that performs searches in spectral libraries and systematic analysis of mixture spectra. It is able to classify IR spectra with the aid of linear discriminant analysis, artificial neural networks, and the method of fe-nearest neighbors. 

The one-electron reduction of thiazole in aqueous solution has been studied by the technique of pulse radiolysis and kinetic absorption spectrophotometry (514). The acetone ketyl radical (CH ljCOH and the solvated electron e were used as one-electron reducing agents. The reaction rate constant of with thiazole determined at pH 8.0 is fe = 2.1 X 10 mole sec in agreement with 2.5 x 10 mole sec" , the value given by the National Bureau of Standards (513). It is considerably higher than that for thiophene (6.5 x 10" mole" sec" ) (513) and pyrrole (6.0 X10 mole sec ) (513). The reaction rate constant of acetone ketyl radical with thiazolium ion determined at pH 0.8 is lc = 6.2=10 mole sec" . Relatively strong transient absorption spectra are observed from these one-electron reactions they show (nm) and e... 

Figure 8.20 Nitrogen Is and oxygen Is X-ray photoelectron spectra of nitric oxide (NO) adsorbed on an iron surface. 1, Fe surface at 85 K 2, exposed at 85 K to NO at 2.65 x 10 Pa for 80 s 3, as for 2 but exposed for 200 s 4, as for 2 but exposed for 480 s 5, after warming to 280 K. (Reproduced, with permission, from Kishi, K. and Roberts, M. W., Proc. R. Soc. Land., A352, 289, 1976)...

The water of hydration of these complexes can be replaced with other coordinating solvents. For example, the ethanol and methanol solvates were made by dissolving the hydrates in triethyl and trimethyl orthoformate, respectively (81,82). The acetic acid solvates are made by treating the hydrates with acetic anhydride (83). Conductivity and visible spectra, where appHcable, of the Co, Ni, Zn, and Cu fluoroborates in A/A/-dimethylacetamide (L) showed that all metal ions were present as the MLg cations (84). Solvated fluoroborate complexes of, Fe +, Co +, , Cu +, and in diethyl... 

Figures The NIE), dN E)/dE, dEN E/dE. and EN E) forms of secondary electron energy spectra from a slightly contaminated Fe surface.

In XPS, chemical information is comparatively slowly acquired in a stepwise fashion along with the depth, with alternate cycles of sputtering and analysis. Examples of profiles through oxide films on pure iron and on Fe-12Cr-lMo alloy are shown in Fig. 2.9, in which the respective contributions from the metallic and oxide components of the iron and chromium spectra have been quantified [2.10]. In these examples the oxide films were only -5 nm thick on iron and -3 nm thick on the alloy. 

Fig. 2.13. Schematic diagram ofthe type of information obtainable from XPS spectra from an Fe-Cr alloy with oxide film underneath a contaminant film [2.57],...

It is relevant to note at this point that, because the metal ions are isoelcctronic, the spectra of low-spin Fe complexes might be expected to be similar to those of low-spin Co ". However, Fe" requires a much stronger crystal field to effect spin-pairing and the ligands which provide such a field also give rise to low-energy charge-transfer bands which almost always obscure the d-d bands. Nevertheless, the spectrum of the pale-yellow [Fe(CN)f,] shows a shoulder at... 

Pyrido[3,4-fe]pyraziii-3- and -2-oiies exist in the enamino forms 171 and 172 respectively in DMSO-dg ( H NMR spectroscopy) and in the solid state (IR spectra in nujol), and temperature appears not to affect these imine-enamine equilibria (97JHC773). 

The pA"a values of 49 derivatives of pyrazol-3-one were measured by poten-tiometric titration and their H NMR spectra were recorded in DMSO- fe- The experimental acidity order correlates for structurally similar compounds as do substituent constants and HMO electron densities (76JPR555). 

Inside the sun, thermal energies are sufficient to destroy all molecules and to ionize the atoms. These ions emit their characteristic line spectra and tens of thousands of lines are observed. The lines that have been analyzed show the existence of atoms ionized as far as 0+5, Mn+I , and Fe+U. At this time, over sixty of the elements have been detected in the sun through their spectral emissions and absorptions. 

Although the o-xylylene complex is thermally unstable, it was characterized at — 50 °C by its 1H- and 13C-NMR spectra showing the exocyclic methylene at 5 = 5.04,4.42 ppm (JH) and 5 = 144.8 ppm (13C) using C6D5CD3 as the solvent. Its reaction with benzoyl chloride on the exocyclic carbon leaves a very acidic methylene group which transfers a proton onto the adjacent methylene unit. The double bond is benzoylated again in in situ and a di-cation of the [bis(arene)Fe]2+ type is obtained [47] Scheme VIII. 

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