Mossbauer spectrum isomer shift

Mossbauer spectroscopy The Mossbauer effect is resonance absorption of 7 radiation of a precisely defined energy, by specific nuclei. It is the basis of a form of spectroscopy used for studying coordinated metal ions. The principal application in bioinorganic chemistry is Fe. The source for the 7 rays is Co, and the frequency is shifted by the Doppler effect, moving it at defined velocities (in mm/s) relative to the sample. The parameters derived from the Mossbauer spectrum (isomer shift, quadrupole splitting, and the hyperfine coupling) provide information about the oxidation, spin and coordination state of the iron. 

The analysis of the Mbssbauer spectra of the three diorganotin(IV) ciprofloxacinate complexes allowed the calculation of the Mossbauer parameters, isomer shifts, 8, and quadrupole splittings, lA I, reported in Table 12.5. Each complex showed the occurrence of a characteristic two doublets spectrum. This indicates that two different tin(fV) environments exist in the organotin polymers. The values of Mossbauer... 

The spin state of the compounds XFe(R2dtc)2 is 3/2 (64). Mossbauer spectra of ClFe(Et2 tc)2 in solution are almost identical with the spectrum of the six-coordinated Fe(Et2magnetic susceptibility and in the isomer shift and quadrupole splitting parameters suggests a geometrical correspondency in solution, which can be attained by the binding of a solvent molecule to the sixth coordination site of the ClFe(Et2[Pg.98]

Interestingly, the correct polarity of the Mossbauer drive can be checked by using the isomer shift of oc-iron with respect to the materials in Table 3.1. After folding of the raw data, the center of the calibration spectrum without further correction must be at —0.12 mm s relative to the Co/Rh source material. 

The isomer shift of a resonance line (or the centroid of a line multiplet) in an experimental Mossbauer spectrum in terms of the Doppler velocity (mm s ) necessary to achieve resonance absorption is given by... 

For a comparison of experimental Mossbauer isomer shifts, the values have to be referenced to a common standard. According to (4.23), the results of a measurement depend on the type of source material, for example, Co diffused into rhodium, palladium, platinum, or other metals. For Fe Mossbauer spectroscopy, the spectrometer is usually calibrated by using the known absorption spectrum of metallic iron (a-phase). Therefore, Fe isomer shifts are commonly reported relative to the centroid of the magnetically split spectrum of a-iron (Sect. 3.1.3). Conversion factors for sodium nitroprusside dihydrate, Na2[Fe(CN)5N0]-2H20, or sodium ferrocyanide, Na4[Fe(CN)]6, which have also been used as reference materials, are found in Table 3.1. Reference materials for other isotopes are given in Table 1.3 of [18] in Chap. 1. 

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...

In a conventional Fe Mossbauer experiment with a powder sample, one would observe a so-called quadrupole doublet with two resonance lines of equal intensities. The separation of the lines, as given by (4.36), represents the quadrupole splitting The parameter Afg is of immense importance for chemical applications of the Mossbauer effect. It provides information about bond properties and local symmetry of the iron site. Since the quadrupole interaction does not alter the mean energy of the nuclear ground and excited states, the isomer shift S can also be derived from the spectrum it is given by the shift of the center of the quadrupole spectrum from zero velocity. 

Fig. 4.9 Magnetic dipole splitting (nuclear Zeeman effect) in pe and resultant Mossbauer spectrum (schematic). The mean energy of the nuclear states is shifted by the electric monopole interaction which gives rise to the isomer shift 5. Afi. g = Sg/tN and A M,e = refer to the...

The first Ni Mossbauer spectrum of nickel in a bioinorganic compound with determinable EFG and isomer shift was reported for a nickel complex compound with planar [NiSJ core and considered as a model compound for hydrogenase. This Mossbauer spectrum from the formal Ni compound is presented in Fig. 7.16. The observed quadrupolar interaction can be understood in terms of ligand field theory. In this approach, the b g and levels (d y2 and d ) are not occupied which is expected to cause a large negative EFG contribution [32]. 

Fig. 7.72 Pt (99 keV) Mossbauer spectrum of the one-dimensional conductor K2[Pt(CN)4] Bro.3o 3H20 at 4.2 K (source Au in platinum at 4.2 K). The solid line represents a single Lorentzian line fitted to the measured spectrum. The dashed line represents the best fit using a sum of two Lorentzian lines with an intensity ratio of 85 15 and with the isomer shifts of the spectra of K2[Pt(CN)4]-3H20 and K2[(Pt(CN)4Br2] (from [333])...

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 Mossbauer spectrum of the dianion was a surprise because the isomer shift (5 = 0.48 mm s ) was substantially more negative than that of the monoanion, and resembles more that of Fe(II)(TPP) than that of [Fe(I)TPP] . Reed and Scheldt therefore suggested a resonance hybrid of iron(I) and iron(II) for the electronic structure of the dianion molecule instead of the formulation [Fe(0)(TPP)] [290, 291]. 

The Mossbauer spectrum of L consists of a symmetric doublet which was fitted with parameters 8 = 0.66 0.02 mm/s and AE = 1.51 0.03 mm/s (71). The isomer shift is larger than values (0.45-0.55 mm/s) generally seen for carboxylate-bridged diiron(III) clusters,... 

What is the structure of this Co-Mo-S phase A model system, prepared by impregnating a MoS2 crystal with a dilute solution of cobalt ions, such that the model contains ppms of cobalt only, appears to have the same Mossbauer spectrum as the Co-Mo-S phase. It has the same isomer shift (characteristic of the oxidation state), recoilfree fraction (characteristic of lattice vibrations) and almost the same quadrupole splitting (characteristic of symmetry) at all temperatures between 4 and 600 K [71]. Thus, the cobalt species in the ppm Co/MoS2 system provides a convenient model for the active site in a Co-Mo hydrodesulfurization catalyst. 

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