Mossbauer spectroscopy hyperfine interactions detected

As will be explained in Chapter 7, spectroscopic methods are a powerful way to probe the active sites of the hydrogenases. Often spectroscopic methods are greatly enhanced by judicious enrichment of the active sites with a stable isotope. For example, Mossbauer spectroscopy detects only the isotope Fe, which is present at only 2.2 per cent abundance in natural iron. Hydrogen atoms, which cannot be seen by X-ray diffraction for example, can be studied by EPR and ENDOR spectroscopy, which exploit the hyperfine interactions between the unpaired electron spin and nuclear spins. More detailed information has been derived from hyperfine interactions with nuclei such as Ni and Se, in the active sites. In FTTR spec-... 

In order to complete the discussion of magnetic hyperfine interactions in paramagnetic heme proteins as detected by Mossbauer spectroscopy, reference should be made to the work of Champion et al. (58). There the influence of the halides F, Cl, and I on ferric chloroperoxidase was studied. The results presented in this work indicate that halide anions,... 

Orbital degrees of freedom are one of the important parameters to discuss the ordered ground states in materials. Orbital occupancy reflects electric field gradient (EFG) at nuclei. Then, Mossbauer spectroscopy can detect orbital occupancy of electrons, especially d or f electron cases. Electronic orbits in f electrons are usually called electronic quadrupole moments. Electronic quadrupole moments directly interact with nuclear quadrupole moments, which are observed as nuclear quadrupole interactions. Since the nuclear quadrupole moment in the Mossbauer transition is relatively large, 3.1 barn, the nuclear quadrupole interaction is relatively easy to detect as asymmetry of spectra even when hyperfine fields are observed. 

This equation corresponds to a static spectrum consisting of two Lorentzian lines centred around (co-I-Act)) and (co—Aco), which is shown schematically in Figure 5.2. In the context of magnetic splitting, the separation of the spectral lines, quantified by Aco, is related to the Larmor precession frequency and Tl the corresponding Larmor precession time, which can be thought of as the measurement time appropriate to the observation of a hyperfine interaction in a Mossbauer spectrum. It is clear that in order to detect the particular interaction it is necessary that Aco T-r, i.e. Tlbasic condition to be fulfilled for observing hyperfine structure in Mossbauer spectroscopy. In the case of Fe this implies that 10 s. 

The probe atoms can be one of the constituents of the material, or they can be impurities introduced into the material from the outside by melting, by diffusion, or by implantation. The former processes make use of the thermal motion of the atoms, while the implantation process injects energetic probe atoms using an accelerator. In this tutorial we will further discuss implantation Mossbauer Spectroscopy , i.e., the probe atoms will be first implanted into a material, and subsequently Mossbauer spectra will be measured by detecting emitted y-rays and electrons. The spectra will provide us with atomistic information on the probe atoms through the hyperfine interactions. This situation may be well compared with an analogy of a spy which is sent to a place to gather information, and he/she will... 

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