Mossbauer spectroscopy other experiments

In this study no other sulfide-containing minerals, except the ones mentioned above, were detected in fresh coals by using Mossbauer spectroscopy. Pyrrhotite was detected in some heavy, weathered coal (Figure 3). The presence of Fe. S was determined by temperature-dependent measurements and the analysis of low-temperature ashes, both by X-ray diffraction and Mossbauer spectroscopy. Other minerals, like spharelite, chalcopyrite, and arsenopyrite, were not detectable in these experiments. Some of the latter minerals have been identified by using scanning electron microscopy, but their presence in the coal was too small to make their contribution to the Mossbauer spectrum significant. 

The results from Mossbauer spectroscopy in applied magnetic fields clearly prove that the spin transition in the dinuclear compounds under study proceeds via [HS-HS][HS-LS][LS-LS]. Simultaneous spin transition in both metal centres of the [HS-HS] pairs converting the dinuclear pairs directly to [LS-LS] pairs can apparently be excluded, at least in the present systems. This is quite surprising in view of the fact that the present dinuclear complexes are centrosymmetric (in other words the two metal centres have identical surroundings, and should therefore experience the same ligand field strength and, consequently, thermal spin transition should occur simultaneously in both centres). 

The present method is still in its early stage of application. Both ex situ and in situ type measurements are applicable to a variety of mineral/aqueous solution interfaces. For example, the mechanism of selective adsorption of cobaltous ions on manganese minerals can be studied by this method. In addition to the two Mossbauer source nuclides described in the present article, there are a number of other nuclides which can be studied. We have recently started a series of experiments using Gd-151 which is a source nuclide of Eu-151 Mossbauer spectroscopy. Development of theory on surface magnetism, especially one including relaxation is desirable. Such a theory would facilitate the interpretation of the experimental results. 

In connection with the problem of oscillations discussed by previous speakers and other types of dynamical behavior of membranes, it would probably be timely to mention here in some more detail the experiments with vision rhodopsin that were performed in our institute by using the Mossbauer spectroscopy method [G. R. Kalamkarov et al., Doklady Biophys., 219, 126 (1974)]. These experiments manifested the existence of reversible photo-induced conformational changes in the photoreceptor membrane even at such low temperature as 77°K. We have labeled various samples of solubilized rhodopsin and of photoreceptor membranes by iron ascorbate enriched with Fe57 and looked for the change of Mossbauer spectra caused by the illumination of our samples. 

As in conventional Mossbauer spectroscopy, Fe is the most widely used isotope in nuclear resonant scattering of synchrotron radiation. Experiments with other... 

Experiments on these synthetic tri-hydroxamic acids have shown the rhombic symmetry effects in the Mossbauer data (Fig. 12). Other experiments using Mossbauer spectroscopy on low symmetry sites have been published by Lang et al. (33) in EDTA and by Zabinski et al. 

We have completed experiments label the ionic domains. We have found evidence of a precipitation phenomenon of particles of iron oxide or hydroxide when an iron form of membrane was exchanged by different other ions like K+, Na+, etc. We therefore have analyzed these particles by different techniques -like X rays, Mossbauer spectroscopy, magnetic measurements and electron microscopy- with two goals in mind. First of all the formation of ultra thin particles is very important in different domains and especially in catalysis when these membranes are used in the solid polymer electrolyte process. Second, we expect some correlation between the sizes and distribution of precipitates with the starting ionic domains. 

Sample purity is a key concern. The NRVS experiment is a bulk technique sampling all Fe nuclei, and impurities that also contain the probe nucleus may confound quantitative data interpretation. Impurities may be introduced during sample preparation or may result from sample instability during measurement. Because of this, care must be taken to ensure purity and reproducibility as Judged by Mossbauer see Mossbauer Spectroscopy), singlecrystal X-ray diffraction, electronic absorption spectroscopy (see Electronic Spectroscopy), Raman spectroscopy or other qualitative techniques. 

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