Isomerization shift

Products of decomposition may be of such small particle size that superparamagnetism is exhibited [329] (e.g. by Fe203 [324,326] where the characteristic six-line spectrum of antiferromagnetic Fe203 is replaced by a doublet with an isomeric shift corresponding to Fe3+). 

The results of the XRD measurement showed that the Fe jAl, jPO catalyst was almost in amorphous state. Only a very broad peak at 29 of ca. 23 degree was observed. The Mossbauer spectroscopic study on this catalyst showed one doublet of iron with the isomeric shift of 0.31 mm s (a-Fe was used as the reference) and the quadrupole splitting of 0.62 mm s. These parameters are very close to those observed for FePO [13, 14], suggesting that the iron cation in the catalyst is tetrahedrally coordinated with oxygen and isolated by four PO tetrahedral units. Such coordination circumstance was suggested to be a key factor for the iron site effective for the oxidation of CH to CHjOH by H -Oj gas mixture [15]. 

Chemical Shifts and Isomeric Shift Differences of (All-f) and (13-Z) Astaxanthin... 

The isomerization shifts conform to those that are described in literature (Englert and Vecci 1980, Englert 1995). All chemical shifts and isomeric shift differences of the olehnic region are listed in Table 4.1. 

To use Equation 2 to determine s electron density diflFerences, it must be "calibrated —i.e., source-absorber or absorber-absorber combinations must be found for which the 5 electron density diflFerence is known. The most common method for calibrating the isomeric shift formula is to measure isomeric shifts for absorbers with diflFerent numbers of outer shell 5 electrons—e.g., by using compounds with the absorbing atoms in different valence states. The accuracy of this method depends on how much is known about the chemical bonds in suitably chosen absorber compounds, in particular about their ionicity and their hybridization. t/ (0) 2 can be obtained for an outer 5 electron from the Fermi-Segre formula or preferably from Hartree-Fock calculations. 

Calibration of the Isomeric Shift Scale with Isomeric and NMR Chemical Shift Data. The alkali iodide isomeric shifts (5) relative to ZnTe are displayed in Table I and in Figure 3. 

The alkali iodide isomeric shifts (13) number of iodine ion p holes calculated rupole resonance data (25) the sum of overlap integrals (11) the fractional iodine ion density computed from the isomeric shift data. Equation 7, and 8. 

From the simple theory of electronegativity an approximately linear relation between the isomeric shift and the alkali electronegativity is expected. This trend is seen when going from Lil to KI (Figure 3) but... 

Figure 6, Compilation of isomeric shifts in compounds. The data converted to scale and is indicated hy dashed lines. A positive velocity corresponds to the ZnTe source moving towards the absorber. Note lack of agreement between shifts for molecular iodine...

One particular species with a high quadrupole splitting A and an isomeric shift of 2.3 mms" is present in all samples. Its relative contribution diminishes when... 

Although low-resolution difference Fourier maps for oxy-Hr and deoxy-Hr show little change in the protein structures, some of the iron center properties are significantly altered in deoxy-Hr. The differences provide a rationale for an oxygen-binding mechanism. The Mossbauer spectrum for deoxy-Hr has a single quadrupole doublet with an isomeric shift typical of high-spin ferrous iron (8 = 1.14 mm/sec AEq = 2.76 mm/sec) (Clark and Webb, 1981). As for met-Hr the two iron environments are similar, yet differ in coordination number for exam-... 

Agresti, Kankeleit, and Persson (I) studied the Mossbauer effect with alloys of 20 atom % Pt in Au and 0.7 atom % Pt in Al, as well as with compounds such as PtO, Pt02, PtCl2, and PtCl4 (Table III) in order to obtain further information about isomeric shifts and possibly electric... 

Figure 9. Plot of the isomeric shift of platinum alloys vs. the electronegativity of the host element.

The deviation for Pt-Al from the general trend might occur because the platinum is not in a solid solution. In the insert, isomeric shifts for some platinum compounds are shown related to the valency of platinum (1). 

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. 

The Mdssbauer Eu spectrum of the composite powder at room temperature is shown in Fig. 3. It presents two lines characterizing by the isomeric shifts 8 = -12.6mm/c, width on half altitude 3.7 mm/c and 5 = +0.02 mm/c with the width on half altitude 4.1 mm/c, respectively. The first line is responsible for the paramagnetic ion Eu of the matrix, and the second line is responsible for the manifestation of Eu ". These isomeric shifts of Eu NGR spectrums in the composite correspond to the position of these ions in the lattice of EuO and EU2O3. 

Ill the presence of hydrogenation catalysts, unsaturated compounds undergo not only hydrogenation but also isomerization—shift of double bonds, or stereochemical transformations—which also affects physical and chemical properties.)... 

Here, Q is the nuclear quadrupole moment (Fe " "), 3(Fe +) and (Fe +), 3(Fe +) are the mean values of the electric field gradients and isomeric shifts for Fe and Fe ions. The coefficients Uvn and a n are found from the solution of the dynamic vibronic problem for the arbitrary values of ct(T). The expressions for and can be obtained by means of the substitution -o- The total Mossbauer spectrum F(Q) was obtained summing the spectra yielded by different cluster vibronic states in the molecular field, taking into account their equilibrium... 

For diiron complexes Mossbauer spectroscopy allows to asses (1) oxidation and spin states of the iron atoms, (2) diamagnetism and ferromagnetism of the groimd state for diferric and mixed-valent oxidation levels and (3) valence (de)localisation in the solid state for mixed-valence complexes [2,3]. Isomer shifts (IS) in the range 0.35-0.60 mm/s are characteristic of 5- or 6-coordinate high-spin diferric p-hydroxo complexes [2,3], Tetrahedral high-spin ferric iron has lower isomeric shifts in the range of 0.22 mm/s [2,3]. For isolated ferric iron with S =... 

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