Hydrogen neutron scattering

Role of adsorbed hydrogen species on ruthenium and molybdenum sulfides. Characterization by inelastic neutron scattering, thermoanalysis methods and model reactions. 

The size and shape of polymer chains joined in a crosslinked matrix can be measured in a small angle neutron scattering (SANS) experiment. This is a-chieved by labelling a small fraction of the prepolymer with deuterium to contrast strongly with the ordinary hydrogenous substance. The deformation of the polymer chains upon swelling or stretching of the network can also be determined and the results compared with predictions from the theory of rubber elasticity. 

Supplementary to other vibrational spectroscopies, inelastic neutron scattering (INS) spectroscopy is a very useful technique for studying organic molecules as it is extremely sensitive to the vibrations of hydrogen atoms. INS spectroscopy has been used to analyze the molecular dynamics of the energetic compound ANTA 5 <2005CPL(403)329>. 

The usefulness of potential energy hypersurfaces in describing reaction dynamics and chemical reactivity is well illustrated by Levine and Bernstein [84] and Shaik et al. [85] books. See also the fundamental paper of Hase [86]. This success does not assure that the coordinate representation of quantum system is necessarily truthful. It goes without saying, the coordinate representation is an extremely useful mathematical model. However, from recent inelastic neutron scattering experiments on hydrogen bonded system, the idea that the BO approximation may be inadequate has been advanced by Kearley and coworkers[87]. 

The presence of hydrogen bonding in water is shown by its anomalous thermophysical properties and has been confirmed by more recent methods of investigating its structure such as NMR, neutron scattering, dielectric relaxation, ultrasonic absorption,... 

Parker, S.F., Taylor, J.W., Albers, R, Lopez, M., Sextl, G., Lennon, D., Mclnroy, A.R., Sutherland, I.W. 2004. Inelastic neutron scattering studies of hydrogen on fuel cell catalysts. Vibration Spectrosc 35 179-182. 

J. Topler, H. Buchner, H. Saufferer, Measurements of the diffusion of hydrogen atoms in magnesium and Mg Ni by neutron scattering, J. Less-Comm. Metals 88 (1982) 397-404. 

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 ... 

We may now discuss the imphcations of the results foimd for the self-motion of hydrogens in the a-relaxation regime by neutron scattering. It is well known that for some simple cases - free nuclei in a gas, harmonic crystals. 

This finding implies a sublinear increase of (r (t)) with time. Thus, the incoherent neutron scattering studies qualify the motion of the hydrogens as an anomalous diffusion involving a sublinearly increasing (r (t)). 

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