Isomer shift calibration constant

The entity ot is the so-called isomer shift calibration constant, c is the speed of light, Co is the electric constant, and Eq is the nuclear transition energy. (The Coulomb constant k = l/(47rco), which was dropped in (4.1), is re-inserted here.) A comprehensive derivation of this expression is found in [8, 9]. 

One calls S the isomer shift. From an electron structure point of view, the parameter of interest is Ap(0) and one combines all other factors into the isomer shift calibration constant a, i.e. 

Relative to the isomer shift of Gd2Cu2Si2 ( + 0.6mm/s versus the EurFd source) or NpCu2Si2 (-h 14.7mm/s versus NpAlj), respectively. The ratio of isomer shift calibration constants is ... 

A calibration of the popular B3LYP and BP86 density functionals for the prediction of Fe isomer shifts from DFT calculations [16], using a large number of complexes with a wide range of iron oxidation states and a span of about 2 mm s for the isomer shifts, yielded a value for the calibration constant a = —0.3666 mm s a.u. (see Chap. 5). Note the negative sign, which indicates that a positive isomer shift of a certain compound relative to a reference material reveals a lower electron density at the nuclei in that compound as compared to nuclei in the reference material. 

Other Iodine Compounds. By studying the isomer shift and the quad-rupole hfs for a series of compounds, Perlow and Perlow (29) have calibrated the isomer shift scale which is independent of Equation 7. The number of p holes, hp, for the compounds of I2, KICI4 H2O, KIC12 H2O, and ICl has been inferred from the measured value of the quadrupole coupling constant, eqQ, and from the symmetry of the iodine lattice site. Since they found that the isomer shifts and hp are linearly related for these compounds, it appears that 5 electrons do not participate directly in the bonding, and the sp hybridization is negligible. Because of this linearity, they have been able to determine dh/dhp, which leads to a calibration of the isomer shift scale. 

Nieuwpoort, W. C., D. Post, and P. Th. van Duijnen (1978). Calibration constant for Fe Mdssbauer isomer shifts derived from ab initio self-consistent-field calculations on octahedral FeFj, and Fe(CN)s clusters. Phys. Rev. B17, 91-98. 

Mossbauer Absorption Spectroscopy. Spectra were acquired at room temperature in a constant acceleration spectrometer using a Co in Rh source. Isomer shifts are relative to the NBS standard sodium nitroprusside. Magnetic hyperfine fields were calibrated with the 515 kOe field of a-FcjO, at RT. Mossbauer parameters were determined by fitting the collected spectra with reference sub-spectra consisting of Lorentzian-shaped lines using a non-linear iterative minimization routine. 

Unfortunately, it is not possible to calculate a (i.e., ACommon practice is a semi-empirical calibration The shift S is measured (with the same source) for two compounds to be considerd rather ionic with the resonant atom in two different charge states. Pertinent examples would be NpFj and NpF. Contact densities calculated with a self-consistent procedure for the free ions are used to obtain Ap(0). The constant a is then determined according to eq. (22). One certainly can raise a number of objections towards this method but it is still the most universal one. It is important, especially for the lanthanides and actinides, that relativistic charge densities p(0) are used. Details concerning isomer... 

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