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J. P. Mariot P. Michaud S. Lauer D. Astruc A. X. Trautwein F. Varret 《Hyperfine Interactions》1983,14(4):333-346
A Mössbauer study of the title paramagnetic Fe(O) complex was carried out from 4.2 K to 250 K. The electric field gradient (EFG) tensor was found to be temperature independent in accordance with the well isolated nature of state3A2g. Measurements in an applied magnetic field of 6 T confirmed the paramagnetic nature (S=1) of the complex and showed the EFG tensor to be negative. From the thermal variation of the hyperfine field we determined the spin hamiltonian constant D=14 K and find the g-value to be close to the free electron value. Semi-empirical molecular orbital (MO) calculations were carried out with a modelized molecule of D6h symmetry; results are in good agreement with the experimental values (for both the electronic and magnetic properties). 相似文献
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Onno de Vegt Herman Vromans Fried Faassen Kees van der Voort Maarschalk 《Particle & Particle Systems Characterization》2005,22(4):261-267
The particle size distribution of fine chemicals in the solid state, like active pharmaceutical ingredients, is often a critical parameter. To achieve the desired particle size distribution, milling of such materials is usually the method of choice. Since these chemicals are often scarcely available, experimental optimization of milling is not possible. Therefore, a model to predict the milling conditions has been developed. The model estimates the rate of breakage function, and needs mechanical properties like hardness and yield strength as input to calculate the rate of breakage function. This paper attempts to check the validity of the model by a series of experiments. A comparison of the experimental results with the outcomes of the model using five different model compounds has been performed. It appears that the rate of breakage function can be estimated by: The model is able to rank the compounds by degree of fracture as an effect of milling. It was also possible to perform a quantitative prediction of the impact of milling pressure on the milling behavior. Finally, it appeared that the prediction of the large particles in the distribution was significantly better than small ones. Because the oversized material is usually the most critical parameter, the conclusion is that the model has acceptable practical applicability. 相似文献
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Hyperfine Interactions - Nuclear forward scattering (NFS) of synchrotron radiation was applied to investigate the electronic and magnetic properties of (i) the diamagnetic... 相似文献
27.
V. R. Marathe A. Sawaryn A. X. Trautwein M. Dolg G. Igel-Mann H. Stoll 《Hyperfine Interactions》1987,36(1):39-58
We have performed ab initio all-electron and pseudopotential MO calculations on FeCO with varying degrees of sophistication
in the basis sets as well as in the calculational procedures. Basis sets with at least double zeta representation for valence
orbitals as well as inclusion of correlation corrections in the MO calculations are the minimum requirements in order to arrive
at a clear decision about the electronic ground state of FeCO. In contradiction to the suggestion given by Guenzburger et
al. [23] we derive from total energy considerations and from comparing experimental and calculated C−O stretching force constants
that the ground state is a spin-quintet (5∑−) and not a spin-triplet. Our calculated quadrupole splitting for MO equilibrium geometry of FeCO5∑− deviates by about 25% from the value which was observed by Peden et al. [1] for FeCO in solid noble gas. However, the calculated
electronic configuration of iron within FeCO5∑− of about 3d6.44s0.8 is far from 3d64s2, which approximately is expected for FeCO when comparing isomer shifts of FeCO and Fe, both matrix-isolated in solid noble
gas, i.e. −0.60 mm/s and −0.75 mm/s, respectively. Thus, at the moment the question remains open to what extent the molecular
properties of FeCO are affected by the solid noble gas matrix. 相似文献
28.
C. Meier V. Schünemann A.X. Trautwein G. Fuchs D. Lowe M. Boll 《Hyperfine Interactions》2000,126(1-4):69-73
The enzyme benzoyl-CoA reductase (BCR) has been studied by Mössbauer spectroscopy in fields up to 7 T and at temperature down to 4.2 K. It has been shown that the oxidized BCR contains three diamagnetic [4Fe-4S]2+ centers. Treatment of BCR with dithionite or deazaflavin reduces only one of the three centers from [4Fe-4S]2+ to [4Fe-4S]1+. The latter exhibits Mössbauer spectra at 4.2 K in applied fields characteristic for Fe2.5+Fe2.5+ (S=9/2) and Fe2+Fe2+ (S=4) pairs, both coupled antiferromagnetically to total spin S=1/2. 相似文献
29.
The four compounds C5H5FeC6H6, C5H5Fe(CH3)6, C5(CH3)5FeC6(CH3)6 and (C6(CH3)6)2Fe+ were studied by Mössbauer spectroscopy on powders. On the basis of semi-empirical molecular orbital calculation (Iterative Extended Hückel with self-consistence of the charge) in which parameters derived from X-ray data are used, we have modelized the thermal behaviour of the electric field gradient (EFG) tensor from 4 K to 300 K. The reduction in magnitude of electronic observables (e.g. spin orbit coupling constant and EFG magnitude) gave evidence for a dynamic Jahn-Teller effect. Spectra in a high magnetic field (6 teslas) confirmed the paramagnetic behaviour of the compounds. The sign of the EFG tensor, the magnetic hyperfine field tensor and its orientation with respect to the EFG tensor were determined. 相似文献
30.