High Mossbauer spectrum

The example is typical for many applications of Mossbauer spectroscopy in catalysis a catalyst undergoes a certain treatment, then its Mossbauer spectrum is measured in situ at room temperature. Flowever, if the catalyst contains highly dispersed particles, the measurement of spectra at cryogenic temperatures becomes advantageous as the recoil-free fraction of surface atoms increases substantially at temperatures below 300 K. Secondly, spectra of small particles that behave superparamagne-... 

Figure 8. Mossbauer spectrum of 7% w/w FePc dispersed on a high surface area carbon (XC-72). The specimen was prepared In the same fashion as described In the caption Fig. 6. The spectrum corresponds to the dry material (19).

The Debye temperature is usually high for metallic systems and low for metal-organic complexes. For metals with simple cubic lattices, for which the model was developed, is found in the range from 300 K to well above 10 K. The other extreme may be found for iron in proteins, which may yield d as low as 100-200 K. Figure 2.5a demonstrates how sharply/(T) drops with temperature for such systems. Since the intensity of a Mossbauer spectrum is proportional to the... 

Fig. 8.38 (Left) The Mossbauer spectrum of the rock called Heat Shield rock, clearly shows with high intensity the mineral Kamacite, an Fe-Ni alloy with about 6-7% Ni (Right) The iron-nickel meteorite Meridiani Planum (originally called Heat Shield Rock ) at Opportunity landing site, close to the crater Endurance. The meteorite is about 30 cm across (Courtesy NASA, JPL, Cornell University)...

The soil close to the crater rim, at the exit point of Opportunity, shows a high hematite content in the Mossbauer spectrum (Fig. 8.36), which can be attributed to the presence of hematite spherules blueberries). 

Reaction of iron(II) chloride with the carbothioamide derivative of bipy, beta (200), gave three compounds, [Fe(bcta)2]Cl2 H20, [Fe(bcta)2][FeCl4], and [Fe(bcta)2]2[Cl3Fe0FeCl3]Cl2 3H20. This last compound contains low-spin Fe and high-spin Fe its Mossbauer spectrum exhibits an unusual temperature dependence." ... 

As expected for a material with cubic sites, the RT spectrum of stoichiometric wiis-tite consists of a single line. The spectrum of the non-stoichiometric material shows an asymmetrically broadened doublet with contributions from Fe " resonance and from two quadrupole split Fe" doublets. The component peaks which contribute to this spectrum have not been fully resolved owing to the range of Fe" environments in the structure (i. e. the variation in Fe content and vacancy level). At 77 K the Mossbauer spectrum consists of a broad doublet with contributions from Fe" and Fe ". Fe(OH)2 shows a sextet corresponding to a Bhf of 16.6 T at 20 K (Miyamoto, 1976 Genin et al. 1986) and to -20 Tat 4K (Refait et al. 1999). The Tn is at 34 K (Miyamoto et al., 1967). The spectrum of high pressure FeOOH at room temperature consists of a sextet (Peret et al. 1973). 

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-... 

Mossbauer spectroscopy of the 57Fe nucleus has been extensively used to investigate aspects of spin equilibria in the solid state and in frozen solutions. A rigid medium is of course required in order to achieve the Mossbauer effect. The dynamics of spin equilibria can be investigated by the Mossbauer experiment because the lifetime of the excited state of the 57Fe nucleus which is involved in the emission and absorption of the y radiation is 1 x 10 7 second. This is just of the order of the lifetimes of the spin states of iron complexes involved in spin equilibria. Furthermore, the Mossbauer spectra of high-spin and low-spin complexes are characterized by different isomer shifts and quad-rupole coupling constants. Consequently, the Mossbauer spectrum can be used to classify the dynamic properties of a spin-equilibrium iron complex. 

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