Mossbauer results

Zuckerman and colleagues473 postulated the first monomeric stannylene on the basis of Mossbauer results on [2,6-(CF3)2C6H3]2Sn in 1981. Ten years later the first... 

Recoilless Optical Absorption in Alkali Halides. Recently Fitchen et al (JO) have observed zero phonon transitions of color centers in the alkali halides using optical absorption techniques. They have measured the temperature dependence of the intensity of the zero phonon line, and from this have determined the characteristic temperatures for the process. In contrast to the Mossbauer results, they have found characteristic temperatures not too different from the alkali halide Debye temperatures. 

The thermal properties of AU55 are treated in Sect. 3, using especially the results of MES measurements [24,25,42]. These are discussed in connection with the concept of bulk versus surface modes in small particles. An explanation of the temperature dependence of the MES [42] absorption intensities and the Cv results [25] on the basis of a model using the site coordination and the center-of-mass motion are briefly reviewed. The consequences of the Mossbauer results for surface Debye temperatures and for the melting temperature of small gold particles are also discussed. 

From the Mossbauer results on Aujj, the thermodynamic behavior of AU55, as well as AugLi " and AuiiL7(SCN)j, at temperatures between 2 K and 30 K can be understood on the basis of the center-of-mass motion of the whole gold core of the material, within the matrix formed by the surrounding ligands. Furthermore, none of these clusters are in the liquid (fluxional) state on the MES time scale, up to at least 30 K. 

Using these "improved parameters for site 1, the trial and error approach was then resumed in order to find a best fit for the site 2 parameters. Subsequently, the ENDOR values for the hyperfine interaction at site 2 were also obtained by Sands and his co-workers (160). Since these values were also in agreement with our own, the final parameters for spinach ferredoxin shown in Table 6 incorporate the combined effort of ENDOR and Mossbauer results, although the ENDOR results give no... 

Solid samples at various stages of conversion were analyzed by Mossbauer spectroscopy. The only product identified in this case was Fe304 Hence, conversions can be calculated based on the weight change data. A comparison of conversions calculated based on the weight change data and those calculated based on the Mossbauer results is shown in Table IV. These results... 

The corresponding high-valent intermediate in the assembly of the di-iron(III) center-tyrosyl radical cofactor of RNR R2 has also been identified by Stubbe and coworkers and designated as X [86,89], This intermediate decays to the (p,-oxo)diiron(III) form at a rate commensurate with the appearance of the tyrosyl radical. Intermediate X, formally Fe(III)Fe(IV), exhibits an isotropic S = 1/2 spin EPR signal near g = 2, which is split by the introduction of 57Fe and broadened by 1702 in the assembly reaction. These observations as well as Mossbauer results show that the unpaired spin must be associated with the diiron center [88,89],... 

Using the Mossbauer results to estimate Aneand Anc, one can attempt to define the net charge flow from the photoemission data. 

Figure 7. Mossbauer spectrum of boiler-wall slag deposits. The approximate phase distribution determined from CCSEM and Mossbauer results is shown in the inset.

The possible sources of error in the point charge analysis have been discussed above. We have attempted to estimate some of these but have not found any that can account for the factor of 3 discrepancy between our results and the Mossbauer results. 

If we have z in the < 111 > direction (trigonal symmetry) and if we again demand that g be isotropic in one doublet, we find that g = 3.3 and a = (—9)D. In this case we begin with trigonal symmetry (A=0). This clearly is no help to us since experimentally we find g =4.3 in ESR and the Mossbauer results also indicate rhombic symmetry. Since several of the iron complexes discussed below are thought to have nominal trigonal symmetry (based on other experiments) we have a bit of a dilemma. 

From the application of the recoilless y-absorption technique to MbCO, HbCO, MbC>2, HbC>2, Mb, and Hb Mossbauer results have been derived which are presented in this section. Fig. 7 shows Mossbauer spectra of a frozen solution of MbCO (pH 7.0) at 4.2 °K (50), a typical candidate for ferrous low-spin state. Curve (a) coresponds to a measurement with zero applied magnetic field. Assuming a Lorentzian line shape (see Table 1), a least-squares fit to this spectrum leads to the following values for the Mossbauer parameters J1 (line width) =0.328 0.011 mm/sec, S (isomer shift, relative to iron metal) =0.266 0.010 mm/sec, and AEq (quadrupole splitting) = 0.363 0.006 mm/sec. Curve (b) shows a spectrum taken with a magnetic field of Ho = 47 kOe applied perpendicularly to the y-beam. Both spectra have been found... 

The final conclusion from a MO interpretation of Mossbauer results then is that in MbCO, HbCO the bonding between the heme iron and the proximal histidine is very weak, the iron is situated in or nearly in the heme plane, in agreement with recent findings (99), the Fe-C distance is somewhat smaller than the typical iron-carbonyl distance of 1.84 A and a Fe-C-0 bond angle of < 180° is more likely than a linear geometry. 

The asymmetry parameters rj(T) (from Table 8) which are related with the AEq(T) and fit curve b of Fig. 28a also agree with the Mb single crystal Mossbauer results. In Ref. (42) the angle a = 40° 8° was derived assuming rj to be zero. A most recent computational analysis of our former Mb single crystal Mossbauer data by Maeda et al. (62), however, indicates that a =40° 8° is consistent also with an -parameter in the range of 0< <0.3. 

Debrunner, P.G., et aL Recent Mossbauer Results of some Iron-Sulfur Proteins and Model Complexes. In Iron-Sulfur Proteins (ed. Lovenberg, W.), Vol. 3, New York, Academic Press 1977, pp. 381-417... 

The XPS data on chemically collapsed phases of SmS (63, 64,65), combined with the Mossbauer result (62), contradict the inhomogeneous mixed valence model. They provide conclusive evidence for the validity of the homogeneous model. In addition they demonstrate that in spite of the fluctuations , the ionic structure of the 4/-shell is maintained, this being a consequence of the fact that Ue > A. 

Although wet chemical techniques are the methods of choice for high precision results when abundant, homogeneous samples are available, opinions about optimal procedures vary (Whipple 1968) and the majority of wet chemical analyses of micas have already been reviewed thoroughly by Foster (1960, 1964). An excellent overview of the Pratt and Wilson wet chemical methods, showing the former method to be more accurate when compared to Mossbauer results, is given in Lalonde et al. (1998). 

Figure 10. (A) Comparison of wet chemical and Mossbauer results on biotites. Results suggest that excellent agreement can be obtained between these techniques, even when Lorentzian line shapes are used to fit the Mossbauer spectra. (B,C) Comparison of XPS data with wet chemical (B) and Mossbauer (C) results on biotites, adapted from Raeburn et al. (1997a,b). (D,E) SmX results on Fe VSFe in micas plotted against wet chemical (D) and Mossbauer (E) data. (F) Comparison of XPS with XANES data on the same samples.

---