Mossbauer spectroscopy applications, generally

From the applications of Ni Mossbauer spectroscopy in solid-state research, it is clear that (1) information from isomer shift studies is generally not very reliable because of the smallness of the observed isomer shifts and the necessity of SOD shift corrections which turn out to be difficult, and (2) useful information about magnetic properties and site symmetry is obtained from spectra reflecting magnetic and/or quadrupolar interactions. 

Mossbauer spectroscopy is particularly suitable to study ST since (1) the spectral parameters associated with the HS and LS states of iron(II) clearly differ and (2) the time-scale of the technique ( 10 s) allows the detection of the separate spin states in the course of the transition. Typically, Mossbauer spectra of HS iron(II) show relatively high quadrupole splitting (AEq 2-3 mm s ) and isomer shift (3 1 mm s ), while for LS iron(II), these parameters are generally smaller (AEq < 1 mm s 3 < 0.5 mm s ). Among the early applications of Mossbauer spectroscopy to study ST phenomena in iron(II) complexes is the work of Dezsi et al. [7] on [Fe (phen)2(NCS)2] (phen = 1,10-phenanthroline) as a function of temperature (Fig. 8.2). The transition from the HS ( 12) state (quadrupole doublet of outer two lines with AEq 3 mm s ) to the LS CAi) state (quadrupole... 

The study of metals in biological systems requires techniques, some of them highly specific, some limited to certain aspects of the metal ion in question, some of more general applicability. Thus, Mossbauer spectroscopy in biological systems is restricted to iron-containing systems because the only element available with a Mossbauer nucleus is 57Fe. The EPR spectroscopic techniques will be of application only if the metal centre has an unpaired electron. In contrast, provided that crystals can be obtained, X-ray diffraction allows the determination of the 3-D structure of metalloproteins and their metal centres. 

The morning session was devoted to a general explanation of the areas of application in studying magnetic properties, oxidation states, compounds, and metal structure. In the afternoon, reviews of the Mossbauer investigations of iron, tin, iodine, tellurium, and some of the rare earth elements were presented. The meeting concluded with a discussion on the future of Mossbauer Spectroscopy in which an interested audience participated. 

Because the greatest limitation for the general use of Mossbauer spectroscopy is that it cannot be observed for all elements, those criteria which restrict the application of Mossbauer spectroscopy to certain isotopes will be discussed in detail in Section II, A. Here, it will be shown which of these Mossbauer isotopes may be used to obtain chemical information, and how these isotopes may also be used to obtain in an indirect manner similar information about elements for which there exists no Mossbauer effect. 

In Section I, C the different Mossbauer parameters were individually discussed with reference to possible catalytic applications. The purpose of that discussion was to provide a physical feeling for the parameters and an appreciation of their possible uses in catalysis. In general, however, for the study of a particular catalytic phenomenon the decision whether also to employ Mossbauer spectroscopy is not based only on the consideration of a single Mossbauer parameter. Thus, in the next sections we discuss, based on a number of examples, the manner in which various catalytic phenomena can be investigated through the systematic employment of the Mossbauer parameters. 

The book opens with a short introduction into the nature of iron oxides. This is followed by a discussion of general preparative techniques (chapter 2). In chapter 3, techniques for characterization of the products - color measurement, electron microscopy. X-ray diffraction, infra red absorption spectroscopy, surface area measurement, thermoanalysis and Mossbauer spectroscopy - are briefly described with particular emphasis on their application to Fe oxides. 

In view of the considerable volume of data available for Fe in metallic systems and the rather tenuous connection of much of it to chemistry, we propose to present in this chapter a selective synopsis. This will illustrate the application of Mossbauer spectroscopy to metallic phases in general from a phenomenological aspect, but a detailed treatment of metal phase-... 

I shall not discuss in further detail general applications of Mossbauer spectroscopy in geochemistry since relevant books, review articles, and original papers are available (1,7,8 9,10). The following sections are devoted to a few selected topics in this field, that is, Mossbauer studies of amorphous minerals and environmental samples. 

Different characterization techniques are used to get an insight into the location of transition metal ions in an aluminophosphate framework. Generally, the data on the cation location are collected with difficulty since the metal concentration is low. In this regard, it is necessary to use more than one method if a reliable conclusion is to be reached (ie, the simultaneous application of several physical techniques is recommended). The following characterization methods are commonly applied diffuse reflectance UV-vis spectroscopy (DRS), electron spin resonance (ESR), electron spin echo modulation (ESEM), infrared (IR), and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopies, as well as the nuclear magnetic resonance spectroscopy (NMR), Mossbauer spectroscopy and the X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption spectroscopy for fine structure (EXAFS) (167,168) and references therein). 

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