Metal Mossbauer spectra

Fig. 5. Mossbauer spectrum of 4 at 4.2 K, source 37Co Rh, Fe metal as standard...

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. 7.34 Mossbauer spectrum of C02RUO4 at 4.2 K with respect to the Ru metal source...

Fig. 7.39 " Ta (62 keV) Mossbauer spectrum of in W metal versus Ta metal absorber at room temperature. The solid line represents the fit of a dispersion-modified Lorentzian line to the experimental data the dashed line shows the dispersion contribution (from [179, 185])...

In catalyst characterization, diffraction patterns are mainly used to identify the crystallographic phases that are present in the catalyst. Figure 6.2 gives an example where XRD readily reveals the phases in an Fe-MnO Fischer-Tropsch catalyst [7], The pattern at the top is that of an MnO reference sample. The diffraction pattern of the reduced Fe-MnO catalyst shows a peak at an angle 29 of 57°, corresponding to metallic iron, and two peaks which are slightly shifted and broadened in comparison with the ones obtained from the bulk MnO reference. The Mossbauer spectrum of the reduced catalyst contains evidence for the presence of Fe2+ ions in a mixed (Fe,Mn)0 oxide [7], and thus it appears justified to attribute the distortion of the XRD peaks to the incorporation of Fe into the MnO lattice. Small particle size is another possible reason why diffraction lines can be broad, as we discuss below. 

We also examined the effects of various heat treatments in both reducing and oxidizing atmospheres. An indochinite reduced for 12 hours in a hydrogen atmosphere at 950 °C. yielded the Mossbauer spectrum displayed in Figure 5. The curve shown is the result of the computer fit the data points are not given, but the closeness of fit is about the same as in the other spectra. The spectrum clearly shows that a certain amount of the original tektite remains the two broad lines at —0.11 and 1.83 mm./sec. match the original tektite lines closely. There is also clear evidence of the presence of metallic iron since the six narrow... 

Mossbauer spectroscopy The Mossbauer effect is resonance absorption of 7 radiation of a precisely defined energy, by specific nuclei. It is the basis of a form of spectroscopy used for studying coordinated metal ions. The principal application in bioinorganic chemistry is Fe. The source for the 7 rays is Co, and the frequency is shifted by the Doppler effect, moving it at defined velocities (in mm/s) relative to the sample. The parameters derived from the Mossbauer spectrum (isomer shift, quadrupole splitting, and the hyperfine coupling) provide information about the oxidation, spin and coordination state of the iron. 

FIGURE 2.1 Energy levels, isomer shift, and quadrupole splitting for 57Fe. The Mossbauer spectrum shown was recorded at T— 4.2 K with a sodium nitroprusside absorber, a diamagnetic (.S 0) compound often used for velocity calibrations. The isomer shift, indicated by the vertical dashed line, has the value 5 — —0.18 mm/s relative to Fe metal. 1 mm/s Doppler shift... 

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