Low energy structural dynamics and constrained libration of Li(NH3)4, the lowest melting point metal.

The lattice and molecular dynamics for the solid phases of the lowest melting-point metal, Li(NH3)4, are determined by incoherent inelastic neutron scattering. Measurements of internal molecular displacements and distortions of the Li(NH3)4 units have been modelled and assigned using density functional theory calculations for the solid and molecular system. Inelastic neutron scattering measurement allow for the first determination of NH3 librational transitions.

Simultaneous measurement of lithium and fluorine momentum in 7LiF.

We present momentum widths and mean kinetic energies of lithium and fluorine in (7)LiF, as determined simultaneously from deep inelastic neutron scattering (DINS) measurements. Experimental data across a temperature range from 4 to 300 K are presented, and these results compared to those calculated using a quasi-harmonic density-functional approach. In all cases, measured momentum widths are seen to be within approximately 5% of those calculated, despite the very low scattering cross sections of both (7)Li and (19)F. This is the first determination and comparison with theory of such simultaneous measurements for nuclei of mass > 4 amu, and demonstrates the implementation of the DINS method in its current form as a mass-selective neutron spectroscopy.

Neutron Compton scattering investigation of sodium hydride: from bulk material to encapsulated nanoparticulates in amorphous silica gel.

In this study we utilize neutron Compton scattering (NCS) to determine differences in nuclear momentum distributions in NaH, both as bulk material and encapsulated as nanoscale particles (from 20 to 50 nm in diameter) within an amorphous silica-gel matrix (SiGNaH). In addition, elemental Na dispersed in such a matrix is also studied (SiGNa). Data treatment and fitting of experimental spectra yields comparison of the nuclear Compton profiles and radial momentum distributions for the proton in both bulk NaH and nanoscale SiGNaH, with resultant proton kinetic energies being in agreement with previous inelastic neutron studies of bulk NaH. Slight differences in proton radial momentum distributions for bulk and nanoscale systems are witnessed and discussed. The technique of stoichiometric-fixing is applied to the backscattering spectra of each system in order to examine changes in the Na profile width, and NCS is shown to be sensitive to the chemical environment change of this heavier nucleus. Examination of the Si and O profile widths in the gel samples also supports this method.

Inelastic neutron scattering of Na-zeolite A with in situ ammoniation: an examination of initial coordination.

The detection and rationalization of the coordination of low concentrations of ammonia within Na-zeolite A is carried out by the application of inelastic neutron scattering (INS), using inverse geometry time of flight spectrometry to study the partial phonon density of states of in situ ammoniated Na-zeolite A. The experimental spectra are subsequently characterised by density functional calculations, incorporating pre-optimisation by geometric simulation. We find that at a concentration of four ammonia molecules per alpha-cage, the ammonia molecule coordinates with extra-framework Na(+) cations and gives rise to three structured regions in the INS spectrum. We show that these regions correspond to translational, librational and tilting motions of the ammonia molecule. These results are in agreement structurally with previous studies of ammonia within a zeolite, and thus show that INS is a valid technique for such investigations.