Neutron Vibrational Spectroscopy Research Articles

Neutron vibrational spectroscopy: The use of hydrogen as a structural and dynamical probe

The large incoherent scattering cross-section of hydrogen combined with an exact knowledge of the form of the scattering function can be utilized in neutron spectroscopic experiments to study local structural environments as well as interaction strengths. An important application of this technique is to focus on a particular hydrogen atom, or hydrogenous molecular group in the material, mainly by employing isotopic substition. Hydrogen is thereby used as a local probe of structure as well as dynamics. Examples include: site geometry and occupancy in metal hydrides, potential well geometry of hydrogen-metal complexes and hydrogen-bonded systems, and dynamical coupling in linear chain hydrogen-bonded materials.

Structure and vibrational spectra of oxonium hexafluoroarsenates(V) and -antimonates(V)

Abstract : The salts OD3(+)ASF6(-), OD3(+)SBF6(-1) and partially deuterated OH3(+)SBF6(-) were prepared and characterized by X-ray and neutron diffraction techniques, DSC measurements, and vibrational spectroscopy. At room temperature, OH3(+)ASF6(-) exists in a plastic phase where ions, centered on the atomic positions of the NaCl structure, are in motion or oscillation. No valuable information on atomic distances or angles in OH3(+)SBF6(-) could be obtained due to these dynamic structural disorder problems. For OH3(+)SBF6(-) the phase transition from an ordered to a disordered phase was shown to occur above room temperature.

Coadsorption and reaction of H 2 and CO on Raney nickel: Neutron vibrational spectroscopy

Neutron inelastic scattering (NIS) has been used to monitor vibrational modes during the adsorption and reaction of hydrogen and CO on Raney nickel. Evidence for a temperature dependent hydrogen/CO interaction is observed. The results show that CO coadsorbed in equivalent amounts with a saturation layer of H at 80 K has little impact on the H vibrational spectrum and thus on the force constant or configuration of the threefold binding sites occupied by hydrogen. Raising the temperature of the CO + H layer to 295 K shows significant H-CO interactions. Preliminary NIS experiments for H 2 CO gas mixtures under flow conditions indicate that the adsorbed layer present under reaction conditions, i.e., during substantial (~50%) conversion of CO to hydrocarbons (450 K) is dominated by the same adsorbates which are found under non reactive (i.e., no conversion of CO to hydrocarbons) conditions (300 K).