Spectrum Mossbauer

Figure 4.54 The effect of an electric field gradient (EFG) creating asymmetry in the electron distribution round a gold nucleus, leading to a quadrupole splitting in the Mossbauer spectrum. (Reproduced with permission from Gold Bull., 1982,15, 53, published by World Gold Council.)...

Figure 4.55 The Mossbauer spectrum of Cs2(AuI2)(AuI4) showing separate resonance from (i) the gold and (ii) the gold(III) sites. (Reproduced with permission from J. Chem. Soc., Dalton...

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

The Mossbauer spectrum of the rearranged compound corresponds with that of a Sn(IV) compound, and the most probable structure appears to be that of a chlorine-bridged dimer. 

Fig. 12. Mossbauer spectrum of an argon matrix containing iron and nickel (59).

CsjFeClsCNjOsli.T has the same Mossbauer spectrum as graphite-FeCl3 F13bl... 

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).

Some early studies [126] on the S-methyldithiocarbazate of 2-formylpyridine, 6, showed it to form low spin iron(III) species, [Fe(6-H)2]C104 and [Fe(6-H)2] [FeCm. The Mossbauer spectrum of the latter showed the presence of two different iron centers, and the compound was a 1 1 electrolyte in nitromethane. 

Two different approaches have been followed to calculate the lineshapes within a relaxation model. According to a phenomenological approach based on the modified Bloch equations [154, 155], the intensity distribution of the theoretical Mossbauer spectrum may be written as [156] ... 

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... 

The recoil-free fraction / is an important factor for determining the intensity of a Mossbauer spectrum. In summary, we notice from inspecting (2.14)-(2.17) and Fig. 2.5a that... 

The expression is known as the transmission integral in the actual formulation, which is valid for ideal thin sources without self-absorption and homogeneous absorbers assuming equal widths F for source and absorber [9]. The transmission integral describes the experimental Mossbauer spectrum as a convolution of the source emission Une N(E,o) and the absorber response exp —cr( )/abs M - The substitution of N E,d) and cr( ) from (2.19) and (2.20) yields in detail ... 

Most Mossbauer spectra are split because of the hyperfine interaction of the absorber (or source) nuclei with their electron shell and chemical environment which lifts the degeneracy of the nuclear states. If the hyperfine interaction is static with respect to the nuclear lifetime, the Mossbauer spectrum is a superposition of separate lines (i), according to the number of possible transitions. Each line has its own effective thickness t i), which is a fraction of the total thickness, determined by the relative intensity W of the lines, such that t i) = Wit. 

The number of beatings in the output signal U t) can be recorded as a function of the channel number simultaneously to the Mossbauer spectrum (usually in a second part of the MCA memory). Accordingly, the number of beats stored in each channel per velocity sweep divided by the dwell time of the MCA channels yields the specific average velocity for each detection channel. 

Fig. 3.12 Contributions to a Mossbauer spectrum given in counts per channel. A b is the nonreso-nant background from scattered y-radiation and X-ray fluorescence in source and absorber...

As discussed in Sects. 3.1.1-3.1.3, successful acquisition of Mossbauer spectra depends on accurate knowledge of the relative velocity of the source and sample. External vibrations that impart differential velocity components to the source and sample would degrade the quality of the Mossbauer spectrum. This degradation... 

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