Isomer shift fluctuating

Other physical properties also show that the iron cores of native ferritins and bacterioferritins are different. Mossbauer spectra of ferritins measured as a function of temperature (Fig. 1) show quadrupole split doublets, with an isomer shift typical of Fe +, gradually being replaced as the temperature is lowered (between about 50 and 15 K) by a magnetic hyperfine spectrum (30, 31). The transition temperature, Tb, is lower than the ordering temperature, Tord (240 K) observed for bulk ferrihydrite (32), because of fluctuations in the direction of mag-... 

Studies on concentrated lanthanide metallic systems have also made it possible to establish a correlation between nonintegral valence (observable in concentrated lanthanide systems through lattice constant, Mdssbauer isomer shift, soft X-ray absorption and X-ray photoemission spectroscopy measurements) and nonmagnetic behavior of a lanthanide ion below the characteristic temperature. This has led to the concept of valence fluctuations (or interconfiguration fluctuations) which has stimulated the current intense activity among theorists and experimentalists alike. 

On the other hand the isomer shift in a Mossbauer experiment on an intermediate-valent system is considered to be slow relative to the intrinsic time scale of the valence fluctuations. The hyperfine interaction of the nucleus with mainly the 5s character electronic charge at the nucleus is an electric monopole interaction (only s electrons can interact with the nucleus, but the 5s electrons being outside the 4f shell are quite sensitive to the occupation of the 4f shell because of different screening of the nuclear... 

If the direction of the main component V z of the electric field gradient (EFG) fluctuates rapidly as a result of diffusion, the Mbssbauer spectrum may be changed in shape. Two atomic sites have very different isomer shift values and the jump between these two states also may show the time-dependent Mbssbauer spectra as a function of the jump firequency. The time scales over which the Mbssbauer effect can be used to observe the dynamical effect is determined by the characteristic times associated with the resonance the natural lifetime and the Larmor precession times of the hyperfine interactions. 

EuXjSij ThCrjSij = Eu 4-700 measured temperature dependence of isomer shifts observed interconfiguration fluctuation (ICE) effects Bauminger et al. (1974a)... 

The large and well-defined range of isomer shifts observed for the NGR of Eu in the di- and trivalent states of the europium ion make this isotope particularly valuable for the study of intermediate valency states in lanthanide intermetallics. Such intermediate valency states have their origin in interconfiguration fluctuations (ICF s). In the case of europium intermetallics, the unusual isomer shifts observed are interpreted in terms of fast fluctuations, on the order of 10 " sec, of an electron between a localized 4f level and the conduction band, resulting in a fluctuating charge density at the Eu nuclei. 

MD simulations with either protein or water constrained at the instant of photoexcitation were performed for both isomer 1 and isomer 2. For isomer 1, because surface water relaxation dominates the slow component of the total Stokes shift, in Fig. 44a we show the result of simulations of isomer 1 with an ensemble of frozen protein configurations to examine the role of protein fluctuations. Clearly the long component of indole-water interactions disappears when the protein is constrained. This result shows that without protein fluctuations, indole-water relaxation over tens of picoseconds does not occur. Thus, although surface hydrating water molecules seem to drive the global solvation and, from the dynamics of the protein and water contributions, are apparently responsible for the slowest component of the solvation Stokes shift for isomer 1 (Fig. 42), local protein fluctuations are still required to facilitate this rearrangement process. When the protein is frozen, the ultrafast... 

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