Using probe molecules with resonant nuclei and nuclear inelastic scattering, we are able to measure the density of states exclusively for collective motions with a correlation length of more than approximately 20 A. Such spectra exhibit an excess of low-energy modes (boson peak). This peak behaves in the same way as that observed by conventional methods. This shows that a significant part of the modes constituting the boson peak is of collective character. At energies above the boson peak, the reduced density of states of the collective motions universally exhibits an exponential decrease.
We have tested the concept of a high-resolution x-ray monochromator with a refractive collimator as an optical element. Two options were examined, where the refractive collimator was included either instead of, or in addition to the first crystal of the high-resolution monochromator. The first approach offers an easy means of improving the energy resolution of conventional optical schemes by few orders of magnitude while still accepting the entire angular divergence of the primary beam. The second approach improves the performance of existing devices with very high-energy resolution and simplifies the design of future optical schemes.
A new method, synchrotron-radiation-based perturbed angular correlations, was applied to study rotational dynamics of Mössbauer atoms in soft condensed matter, using incoherent nuclear resonant scattering of synchrotron radiation. A theory was developed that describes the correlations for the scattering by an ensemble of randomly oriented spins under the influence of rotational relaxation. In a feasibility study a molecular glass former doped by probe molecules was investigated above the glass transition up to the normal liquid state. A comparison of the obtained rotational relaxation rates with data from dielectric spectroscopy shows that the probe molecules reproduce the dynamics of the glass former.
Keywords: Carboxylate ligands / EPR spectroscopy / EXAFS spectroscopy / Mössbauer spectroscopy / OxidationA series of 2,6-diacylpyridine ligand precursors 5a-d·HCl with different tether lengths between the carboxyl and pyridine moiety was prepared and converted into the correspondig trinuclear Fe 3 (µ 3 -O) complexes 8a-d and 10. Under slow precipitation conditions a tetranuclear complex 9 was isolated instead of 8a. Single-crystal X-ray diffraction analyses were performed on ligands 5a-d and complexes 9 and 10. Characterization by X-ray absorption spectroscopy (XAS) proved a trinuclear Fe 3 (µ 3 -O) core for complexes 8a-d. When complex 8a was submitted to Gif-type oxidations (O 2 , Zn, pyridine, HOAc), Mössbauer and nuclear inelastic scattering (NIS) suggested the formation of mononuclear species. The trinuclear ferric complex 10 has an isosceles molecular structure, which is manifested in the 57 Fe Mössbauer spectrum
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