Temperatures, Mossbauer studies

Zunmermann et aL3° have further undertaken high field and variable temperature Mossbauer studies that resulted in a set of parameters (Table 3) which characterize the ferrous state of the enzyme these parameters should prove useful for the design of appropriate synthetic model complexes. 

Mossbauer spectroscopy has proved to be of great value in inorganic tin chemistry (Table 6). Particularly useful have been isomer shift (5) and quadrupole splitting (A) data. The recoil-free fraction and its temperature coefficient are other parameters that have found use in structural elucidations variable temperature Mossbauer studies can be used, for example, in gaining information regarding the degree of aggregation in solid tin compounds. 

Bolivar, F., Meneses, C.A.B., Minotas, J., Greneche, J.M. Variable temperature mossbauer study of some rust converters. Hyperfine Interact 148, 219-225 (2003)... 

In Sm3S4 and EU3S4, ordering of the di and trivalent cations occurs at sufficiently low temperature. Mossbauer studies (Berkooz et al., 1968), an electrical transition near 175 K (Bransky et al., 1970), differential thermal analysis, magnetic data and X-ray studies (Davis et al., 1970) all show up this ordering which causes a tetragonal distortion of the cubic cell (cla = 1.004), at 168 K for EU3S4. 

L.K. Leung, B.J. Evans, A.H. Morrish, Low temperature Mossbauer study of a Nickel-Zinc ferrite ZnxNii xFe204. Phys. Rev. B 8, 29 3 (1973)... 

The same magnetic dependence on temperature was also demonstrated for unsolvated Fe[papt] (694). and a detailed Mossbauer study established that the spin transition is thermally... 

A major discrepancy that remains unresolved in the excited-state properties of the [Fe384]° cluster in D. gigas Fdll concerns the existence of a low-lying, fully valence-delocalized state that becomes populated at temperatures above 25 K. 8uch a state is clearly apparent in the temperature-dependent Mossbauer studies of reduced D. gigas Fdll (29) and P. furiosus 3Fe Fd (198) and is represented by one quad-rupole doublet with AEq 0.9 mm/s and S = 0.45 mm/s. 8uch a... 

An important advance on these studies was the possibility of isolating AORs from Fe enriched media with obvious interest for an iron-sulfur center site labeling, with enhanced sensitivity of the Mossbauer studies. The work developed with bacterial systems is advantageous as compared with mammalian systems for isotopic labeling and opens the possibility of a direct measurement of substrate binding. Spectra of the enzyme in oxidized, partially reduced, benzaldehyde-reacted, and fully reduced states were recorded at different temperatures and with variable externally applied magnetic fields (222). In the oxidized enzyme, the clusters are diamag-... 

Another study of the temperature dependence of the 6.2 keV Mossbauer resonance of Ta has been carried out by Salomon et al. [197] for sources of WAV metal and W/Ta metal in the temperature range from 15 to 457 K. In more recent investigations, Salomon et al. [198] have extended such studies of the temperature behavior of the 6.2 keV Mossbauer transition of Ta in tantalum metal to temperatures up to 2,300 K which has been the highest temperature range for any Mossbauer study so far. 

Gold is the only known dopant to YBa2Cu307, 5, which increases the critical temperature Tc of transition to the superconducting state. In this way, is enhanced from 97 K by 1.5 K. Eibschiitz et al. [401] observed by Mossbauer studies that the... 

The structural picture that was envisaged to represent the temperature-dependent fluctuations of the EFG tensor [15] is based on the X-ray structure of MbOa that exhibits a geometric disorder of Fe02 with two different positions of the terminal O-atom [28]. Within this stmcture, the projection of the 0-0 bond on the heme plane is rotated by about 40° in position 2 compared to 1 (Fig. 9.10). Conventional Mossbauer studies of single crystals of Mb02 have shown that the principal component of the FFG tensor lies in the heme plane and is oriented along the projection of the 0-0 bond onto this plane [29]. If the terminal O-atom is located in position 2, the EFG should be of the same magnitude as in position 1, but its orientation is different. The EFG fluctuates between positions 1 and 2 with a rate that depends on temperature. 

Mossbauer Spectroscopy. Figure 1 shows room temperature Mossbauer emission spectra of two of the unsupported Co-Mo catalysts which we have studied in the present investigation. It is observed that the MES spectra of the two catalysts are quite different. For the catalyst with the low Co/Mo ratio (0.0625), a quadrupole doublet with an isomer shift of 6=0.33 mm/s and a quadrupole splitting of AE =1.12 mm/s are observed (spectrum a). These parameters are very similar to those observed previously for the Co-Mo-S phase in other catalysts (6-9). Furthermore, the spectrum of an unsupported catalyst with Co/Mo = 0.15 is found to be essentially identical to spectrum (a). The MES spectrum (b) of the catalyst with Co/Mo =... 

Genin, J.M., Bauer, P., Olowe, A.A. Rezel. D. (1986) Mossbauer study of the kinetics of simulated corrosion process of iron in chlorinated aqueous solution around room temperature. The hyperfme structure of ferrous hydroxide and green rust. Hyp. Interact. 29 1355-1360... 

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