Mossbauer spectrum electric quadrupole splitting

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...

Figure 4.54 The effect of an electric field gradient (EFG) creating asymmetry in the electron distribution round a gold nucleus, leading to a quadrupole splitting in the Mossbauer spectrum. (Reproduced with permission from Gold Bull., 1982,15, 53, published by World Gold Council.)...

Fig. 4.6 Quadrupole splitting of the excited state of Fe with I = 3/2 and the resulting Mossbauer spectrum. Quadrupole interaction splits the spin quartet into two degenerate sublevels 7, OT/) with energy separation A q = 2 q. The ground state with I = 1/2 remains unsplit. The nuclear states are additionally shifted by electric monopole interaction giving rise to the isomer shift 8...

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... 

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 ... 

The Mossbauer effect is sensitive to the oxidation and spin state of iron and the environment around the iron nucleus therefore different chemical species yield different Mossbauer spectra. Furthermore all spin states and oxidation states of iron are accessible to the technique. There are three main components of a Mossbauer spectrum. The isomer shift arises from the electron density at the 57Fe nucleus the quadrupole splitting results from the electric field gradient produced by electrons and ions around the 57Fe nucleus, and the nuclear Zeeman splitting is sensitive to the spin state and magnetic coupling of the iron. 

The very characteristic oxidation reactions of these substances probably occur through removal of one or more of these nonbonding electrons. The magnetic susceptibility of the ferricenium ion (2.49 BM) 52) is in accord with the E2g state for this ion, as is a recent Mossbauer determination of the sign of the electric field gradient in ferrocene 9) and the observed decrease in quadrupole splitting in the Mossbauer spectrum of ferrocene on oxidation to the ferricenium ion 69). 

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.

YbNiSn was intensively investigated by °Yb Mossbauer spectroscopy in the paramagnetic and in the ferromagnetically ordered state (Bonville et al. 1992, Bellot et al. 1992). The 1.48 K spectrum shows hyperfine field splitting with five well-resolved lines with an experimental linewidth of about 3 mm/s (fig. 16). Due to the non-cubic ytterbium site, a quadrupolar hyperfine term with an electric field gradient is observed. In the paramagnetic phase (6K measurement) the spectrum shows two resolved lines which result from quadrupole splitting. 

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