Time quasi-elastic neutron scattering

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... 

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). 

Probability to find a particle at position r at time t Pulsed-field gradient nuclear magnetic resonance scattering vector Quasi-elastic neutron scattering General position vector of nucleus... 

The combination of quasi-elastic neutron scattering (QENS) and neutron spin-echo (NSE) methods allows one to probe characteristic times ranging... 

Nowikow et al. (1999) measured the self diffusion of water in 0.94 m BU4NCI at room temperature using quasi-elastic neutron scattering. The residence times of water molecules in the hydration shell of the cation were twice longer than in bulk water. Still, (1 - Z>w(E)/-Dw) > 0 and the salt is a net structure maker. Sacco et al. (1994) measured the self diffusion coefficient of the water in aqueous CsCl in D2O... 

The quasi-elastic neutron scattering from H2O and D2O, in harmotome, has been further measured in samples with 2, 4, and 12 water molecules per unit cell at 294 K < T < 423 K [98S1]. From the observed coherent scattering relaxation time for D-D correlations, 2 to 11 ps were obtained. Fitting the incoherent quasi-elastic peaks from H2O to a two site jump model, yielded residence times of the protons in the range from 4 to 6 ps [98S1], close to the previous reported values. 

Quasi-elastic Neutron Scattering. Coherent and incoherent inelastic neutron scattering are unique experimental techniques to characterize molecular motions on a time scale between 10 and 10 s. The continued development of high resolution inelastic scattering techniques in the past two decades (157-159) enables measurement of the dynamic structure factor S(Q, co) and the... 

This work shows that the observation of motions which occur on different time scales can be made from quasi-elastic neutron scattering by performing experiments on spectrometers working at different energy resolutions. It shows that QNS is a very powerful tool to study the spatial dependence of H-motions and that models for the motions can be easily formulated starting from structural results. 

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