Mossbauer quadrupole hyperfine interactions

Mossbauer measurements with determination of the electric quadrupole moments have been reported in [253, 254,259]. Wagner et al. [254] measured the quadrupole hyperfine interaction in OSO2 and OSP2 of the Mossbauer isotopes The ratios of the quadrupole moments of the 4 = 72 states in the even osmium isotopes and of the 4 = 5/2 (69.6 keV) and 4 = 3/2 states in Os were deduced very accurately. In Table 7.8, the experimental results [254] are given, from which the following ratios can be calculated ... 

The first reported Mossbauer spectrum of a-Fe203 was by Kistner and Sunyar [1], who thereby recorded the first chemical isomer shift and electric quadrupole hyperfine interactions to be observed by this technique. With a single-line source the room-temperature spectrum comprises six lines from a hyperfine field of 515 kG the chemical isomer shift (Table 10.1) is... 

In practical applications it may happen that the magnetic and quadrupole hyperfine interactions occur simultaneously and the spectra are superimposed on one another. Such a case for iron is presented in Fig. 11 where the effect of first-order quadrupole perturbation on a magnetic hyperfine spectrum is shown. It is evident that the detailed interpretation of this Mossbauer spectrum is quite complex. 

Fig. 11. Superposition of the magnetic and quadrupole hyperfine interactions at a Mossbauer isotope...

The quadrupole splitting. A, is the Mossbauer parameter, which is related to the electric quadrupole hyperfine interaction between the nucleus and the electrons (see Sect. 25.1.5.2). 

The two absorption peaks, appearing in the measured Mossbauer spectrum as a consequence of electric quadrupole hyperfine interaction, are called a doublet. 

Pure nuclear magnetic hyperfine interaction without electric quadrupole interaction is rarely encountered in chemical applications of the Mossbauer effect. Metallic iron is an exception. Quite frequently, a nuclear state is perturbed simultaneously by... 

Fig. 4.13 Combined magnetic hyperfine interaction for Fe with strong electric quadrupole interaction. Top left, electric quadrupole splitting of the ground (g) and excited state (e). Top right first-order perturbation by magnetic dipole interaction arising from a weak field along the main component > 0 of the EFG fq = 0). Bottom the resultant Mossbauer spectrum is shown for a single-crystal type measurement with B fixed perpendicular to the y-rays and B oriented along...

We have learned from the preceding chapters that the chemical and physical state of a Mossbauer atom in any kind of solid material can be characterized by way of the hyperfine interactions which manifest themselves in the Mossbauer spectrum by the isomer shift and, where relevant, electric quadrupole and/or magnetic dipole splitting of the resonance lines. On the basis of all the parameters obtainable from a Mossbauer spectrum, it is, in most cases, possible to identify unambiguously one or more chemical species of a given Mossbauer atom occurring in the same material. This - usually called phase analysis by Mossbauer spectroscopy - is nondestructive and widely used in various kinds of physicochemical smdies, for example, the studies of... 

The oxygenated form of the protein has a Mossbauer spectra consisting of two pairs of quadrupole fines indicating two distinct Fe sites. Again there is no evidence of hyperfine interaction down to 4 °K. The attribution of one pair of lines to impurities by Okamura et al. (181) has now been retracted by this group of researchers (189). 

Hm describes the hyperfine interaction with the 57Fe nucleus. A is the magnetic hyperfine tensor and Hq describes the interaction of the quadrupole moment Q of the 7=3/2 nuclear excited state with the (traceless) electric field gradient (EFG) tensor V (the nuclear ground state has 7= 1/2 and lacks a spectroscopic quadrupole moment). In the absence of magnetic effects (for instance, for S 0, or S = integer for B = 0), the Mossbauer spectrum consists of a doublet with quadrupole splitting ... 

In case of Fe, the resonant absorption of 14.4keV y-rays emitted by a radioactive Co source is measured. The spectra are determined by the hyperfine interactions (isomer shift, quadrupole sphtting, and magnetic hyperfine field) of the Mossbauer nucleus caused by the surrounding electron shell. 

Mossbauer spectroscopy senses the hyperfine interactions, which are present at the nucleus of the Mossbauer isotope. The electrical monopole interaction causes the isomer shift and the electric quadrupole interaction leads to the quadrupole splitting, which in the case of Fe causes a two-line Mossbauer pattern. The magnetic dipole interaction leads to a magnetically split six-line pattern (Figure 4). In the following text, these interactions and their deduction from Mossbauer spectra will be discussed. 

Figure 1. Hyperfine interactions for Fe nuclei, showing the nuclear energy level diagram for (a) an unperturbed nucleus (b) electric monopole interaction (isomer shift) (c) electric quadrupole interaction (quadrupole splitting) and (d) magnetic dipole interaction (hyperfine magnetic splitting). Each interaction is shown individually, accompanied by the resulting Mossbauer spectrum.

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