Incoherent quasi-elastic neutron

To date, incoherent quasi-elastic neutron scattering experiments on the a-relaxation regime of glass-forming polymers have revealed the following main features for the self-motion of hydrogens ... 

A primary hydration number of 6 for Fe + in aqueous (or D2O) solution has been indicated by neutron diffraction with isotopic substitution (NDIS), XRD, 16,1017 EXAFS, and for Fe " " by NDIS and EXAFS. Fe—O bond distances in aqueous solution have been determined, since 1984, for Fe(H20)/+ by EXAFS and neutron diffraction, for ternary Fe " "-aqua-anion species by XRD (in sulfate and in chloride media, and in bromide media ), for Fe(H20)g by neutron diffraction, and for ternary Fe -aqua-anion species. The NDIS studies hint at the second solvation shell in D2O solution high energy-resolution incoherent quasi-elastic neutron scattering (IQENS) can give some idea of the half-lives of water-protons in the secondary hydration shell of ions such as Fe aq. This is believed to be less than 5 X I0 s, whereas t>5x10 s for the binding time of protons in the primary hydration shell. X-Ray absorption spectroscopy (XAS—EXAFS and XANES) has been used... 

Gardner, A. B., Howard. J., Waddington, T, C., Richardson, R. M. and Tomkin-son, J. The dynamics of ring rotation in ferrocene, nickelocene and ruthenocene by incoherent quasi-elastic neutron scattering. Chemical Physics 57, 453-460 (1981). 

Feeney, M., Brown, C., and Tsai, A. Incoherent quasi-elastic neutron scattering from fructose-water solutions, /. Phys. Ghent. B, 105, 7799, 2001. 

Figure 11. Incoherent quasi-elastic neutron scattering spectrum obtained with a 220 C dehydrated acid Nafion sample = 0.59 A )...

Incoherent quasi-elastic neutron scattering from diffusing hydrogen atoms allows us to investigate the elementary jumps involved in the tracer diffusion process. 

All alkali ions and Ca +, Sr + and Ba + are very labile as a consequence of their relatively low surface charge density. The only direct experimental data on water exchange in some of these ions comes from incoherent quasi-elastic neutron scattering (IQENS) [74-76]. IQENS has an observation time scale fobs 1 ns and allows for the calculation of limits for ion to water-proton binding times Tj (Table 4.4). Mean lifetimes of H2O in the first shell of Ca + and Sr " can be estimated to 0.2 ns from the chemically similar Eu " ion (see Sect. 4.3.2). 

The incoherent scattering cross section of hydrogen is exceptionally large so incoherent quasi-elastic neutron scattering is dominated by the motion of hydrogen atoms, which simplifies the interpretation. 

Background to Incoherent Quasi-Elastic Neutron Scattering (IQENS)... 

The same incoherent quasi-elastic neutron scattering methods have been used to probe the molecular dynamics of more complex systems. Fatty acid salts of copper form a disk-like molecule comprising a binuclear core with four chains extending from it, and these can form a columnar mesophase where the disks are stacked. Copper palmi-tate has been examined in its crystalline phase and in a columnar mesophase. The quasi-elastic scattering was interpreted in terms of the motion of the alkyl chains. Each methylene group explored a spherical volume and the radius of the sphere increased with distance from the copper core [68], A later experiment on oriented fibers of copper laurate [69] showed that this motion was anisotropic with a greater amplitude in the plane perpendicular to the columns. 

IQENS incoherent quasi-elastic neutron scattering... 

Incoherent quasi-elastic neutron scattering (IQENS) has been used to investigate the dynamics of nematic phases. When a monochromatic beam of neutrons is scattered from a nematic liquid crystal the shape of the elastic line in the energy-transfer spectra gives information on the molecular dynamics. A quasi-elastic neutron scattering measurement may be used to investigate the diffusive motions of the molecules in the nematic phase. The translational diffusion coefficients may be determined and localised motions such as molecular rotation and internal rotations may also be characterised. 

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