Mossbauer parameters, temperature

In addition to the four detectors used to detect backscattered radiation from the sample, there is a fifth detector to measure the transmission spectrum of the reference absorber (a- Fe, a- Fe203, Fc304 see Fig. 3.16). Sample and reference spectra are recorded simultaneously, and the known temperature dependence of the Mossbauer parameters of the reference absorber can be used to give a measurement of the average temperature inside the SH, providing a redundancy to measurements made with the internal temperature sensor (see Sect. 3.3.4). 

During the mission, the magnetite CCT was measured in several runs to verify the functionality of MIMOS II. The well-known Mossbauer parameters of magnetite were used for velocity calibration, as shown in Fig. 3.22 for different temperatures. This kind of measurement was done in the laboratory with the flight units as a function of temperature to be used as a reference for the measurements on Mars. Figure 3.22 shows the Mossbauer spectra of the CCT at different mean temperatures. 

The main objective in carrying out LIESST experiments on (bt, S) was to elucidate the nature of excitations (metastable pairs) which appear at low temperatures after light irradiation of a ground [LS-LS] state. As is illustrated in Fig. 11a, at 4.2 K before irradiation the Mossbauer spectrum of a sample, which was enriched with 20% of 57Fe, reflects the presence of mainly LS species. The Mossbauer parameters obtained from the fitting of the spectrum are dLs=0.357(l) mms, AEq(ls)=0.452(2) mms. After irradiation of the sample for one hour (2=514 nm) at 4.2 K, the Mossbauer spectrum of (bt, S) shows a decrease in the intensity of the LS species (62.0%) in favour of an increase of the HS species (38.0%) (Fig. lib). Time-dependent measurements revealed the decay of the HS component (Fig. 11c, d), which... 

Table III. Room Temperature Mossbauer Parameters of Ferric Metaphosphate (19)"...

The magnetic properties of deoxyHr indicate that a bridge between the iron centers persists but may be altered from that in oxyHr. The NMR spectrum of deoxyHr exhibits large isotropic shifts for the N-H s on histidines coordinated to the binuclear unit. Mossbauer parameters of deoxyHr (Table II) are typical of high spin iron(II) centers which are at best weakly coupled (37,38,39). Room temperature magnetic susceptibility measurements using the Evans NMR technique... 

Mossbauer spectra are used for identification and and characterization of Fe oxi-des.This follows primarily from the fact that the different Fe oxides order magnetically over a wide range of temperatures from 950 down to below 78K. The Mossbauer parameters of the various magnetically ordered Fe oxides differ considerably and thus allow unequivocal identification and often quantification in mixtures to be made. Mossbauer spectroscopy is insensitive to all isotopes except Fe (and a few... 

AT-Phcnyl-AT,-(2-thiazolyl)guanidine forms 2 1 complexes with Cu11 and Hg11 and 1 1 complexes with WV1 and Movl as indicated by absorption spectra, conductometric and amperometric measurements.171 Room temperature Mossbauer parameters have been tabulated for dehydro-A, A, A"-trialkylguanidinohexacarbonyldiiron(O) and related compounds.172... 

The manifestations of mobility in the Mossbauer parameters are perhaps best introduced with reference to a series of papers by the Russian Laboratory at the Institute of Chemical Physics in Moscow (115-120). Several examples from this series will demonstrate the underlying principles. One system studied was tin (using the 119Sn, 23.9-keV transition) on 300 m2gm-1 silica gel. The Mossbauer spectra of this sample are characteristic of both SnO and Sn02 H20 components being present in approximately equal proportions (115), and it is from the temperature dependences of the respective spectral areas that information about the mobilities of these two species... 

The advantage of the technique is that the particle size may be determined with the sample in a controlled atmosphere and at a temperature different from 300 K, i.e., in situ particle size measurement, and measurement of changes in particle size may be possible. The problem, however, is that the quantitative relation between the Mossbauer parameters and particle size is rather complex and in some cases not theoretically available. Therefore, the application of the Mossbauer effect to particle size measurement is often facilitated through an experimental calibration of the Mossbauer parameters to particle size for the particular catalyst system of interest, i.e., the measurement of the parameters for a set of samples of known particle size as determined by other experimental methods. This point will become clearer below, as the effects of particle size on the Mossbauer parameters are discussed. 

The results of this analysis are shown in Table II, after it was found that four peaks provided the most meaningful fit of the data (low y-squared with physically realistic Mossbauer parameters). The outer two peaks form a doublet whose isomer shift is that expected for high-spin Fe2+, and whose quadrupole splitting is temperature dependent, reflecting the change with... 

Table 5. Mossbauer parameters for the high temperature reduced PPNR spectra...

Table 22 Mossbauer Parameters for Iron(II) Phthalocyanine and Selected Derivatives at Room and Liquid Nitrogen Temperatures...

Table 3. Mossbauer parameters at 4.2 K and room temperature magnetic moments of linear MoS2Fe clusters...

---