Incoherent Inelastic Neutron Scattering Spectra Research Articles

Incoherent Inelastic Neutron Scattering Studies of Nanoconfined Water in Clinoptilolite and Heulandite Zeolites

In a continued effort studying the role of water in ion exchange processes of zeolites, a synthetic series of alkali and alkaline earth metal cation variants (Na+, K+, Rb+, Mg2+, and Ca2+) of the hydrated clinoptilolite (Si/Al ≈ 5) and heulandite (Si/Al ≈ 3.5) aluminosilicate zeolites is examined by incoherent inelastic neutron scattering (IINS). The low-frequency librational modes of water reveal the impact of nanoconfinement and framework charge within these isostructural aluminosilicate structures. The experimental IINS spectra are correlated with power spectra derived through molecular dynamics simulations. The impact of ion−zeolite, ion−water, and water−zeolite interactions on the hindered rotations (librations) of water molecules is explored as a function of Si/Al substitution, cation identity, and subnanometer confinement. The results indicate that electrostatic charge on the overall framework has a stronger influence than charge density of a given ion in the channel and that these effects become m...

Vibrational dynamics of ethylene glycol in mesoscopic confinement by incoherent inelastic neutron scattering (IINS) investigation

In this paper, we go deeply into an analysis performed, as a function of T, by means of incoherent inelastic neutron scattering (IINS), of vibrational dynamics of liquid ethylene glycol (EG: HO–CH 2CH 2–OH) in the bulk state and confined into 26 Å interconnected cylindrical pores of a sol-gel porous glass. IINS spectra revealed, as far as the vibrational density of states, Z( ω) is concerned, a different trend in temperature passing from bulk to confined samples. In particular, we observed a thermal stabilization of the disordered longitudinal acoustic mode as a consequence of the interaction between the hydroxyl groups (OH) of the EG molecules and the active silanol groups (Si–OH) on the surface of the porous glass.

Incoherent inelastic neutron-scattering studies of the structure of water associated with DNA and gelatin

Incoherent inelastic neutron-scattering spectra of DNA and gelatin samples with different hydration levels were measured with the TOSCA spectrometer at ISIS, Rutherford Appleton Laboratory. Comparison with the spectra of different ice phases shows that for water contents up to 0.75 g water/g DNA and 0.5 g water/g gelatin the optical region (20–50 meV) is almost featureless, similar to high-density amorphous ice (HDA). The librational band is shifted to lower energy transfers and its edge at 55 meV matches again the spectrum of HDA ice. For water contents of 1 g water/g DNA and 0.75 g water/g gelatin resemblance to spectra of ice Ih and low-density amorphous ice (LDA) is obvious. PACS Nos.: 61.12Ex, 82.39Jn

The Effects of Solvent and Anharmonicity on Incoherent Inelastic Neutron Scattering Spectra of Proteins

We investigated the protein energy landscape using molecular dynamics simulation and normal mode analysis. The dynamical structure factor of a protein, staphylococcal nuclease (SNase), is calculated from the model calculations based on the Jumping-Among-Minima (JAM) model. In this model, the protein dynamics is described in terms of two types of motions: intra- and inter-substate motions. These results are compared in order to investigate the effects of solvent and anharmonicity on protein dynamics. From the comparison of the structure factors, we derive information on the nature of the dynamics in the low frequency region.

Incoherent inelastic neutron scattering measurements on dome-fuji antarctic ice

We measured the incoherent inelastic neutron scattering (IINS) in ice (depth, 201–2201 m) recovered from Dome-Fuji (DF), Antarctica. We found that the peak intensity of librational vibration in the IINS spectra of DF ice changes with the ice temperature (Ti) in the ice sheet: the intensity at 97 meV decreases with increases in depth from 201 to 2201 m. From the IINS spectra, we calculated the Ti dependence of the order parameter (the ratio of ordered protons in ice), which is consistent with the theory of the order-disorder phase-transition from proton arrangements in ordinary ice to proton-ordered arrangements at Ti = 237 K. The results indicate that Antarctic ice in which Ti ≤ 237 K contains proton-ordered arrangements.

Low-energy vibrations and octahedral site occupation in Nb95V5H(D)y

Nb100−xVxHy is a random b.c.c. alloy system with an H sublattice disordered with respect to site energies. Previous incoherent inelastic neutron scattering (IINS) studies ascertained both octahedral (o) and tetrahedral (t) site occupation by H for x = 50, 10and50. On the basis of spectroscopic and statistical arguments, the low-temperature H vibrational peaks in the Nb-rich, low-H-concentration Nb95V5H1 alloy were assigned to Nb4V2 o sites and NbV3 t sites. To probe the regime of lower H concentration and the effects of D substitution, further IINS spectra were measured for Nb95V5Hy (y = 0.5and0.8) and Nb95V5D2.7. As the H concentration was decreased, the spectra at 4 K indicated an increasingly predominant 38 meV peak, which was assigned to the doubly degenerate H vibrations in the Nb4 plane of the Nb4V2 o site. A portion of the board feature centered at approximately 200 meV was assigned to the much stiffer H vibration polarized along the V-V apical axis. The Nb95V5D2.7 results located the analogous soft D vibration at 29 meV, yielding an H/D vibrational energy ratio of 1.31. To our knowledge, this is the only known case of spectroscopically confirmed o-site occupation by H in a b.c.c. metal (alloy) lattice. Moreover, the soft modes yield the lowest observed vibrational energy for H in a metal hydride.

Hydrostatic pressure and temperature dependence study of d-camphor and dl-borneole by neutron scattering

Abstract Neutron scattering investigations have been performed down to helium temperatures under different hydrostatic pressures up to 330 MPa. Neutron diffraction (ND) and incoherent inelastic neutron scattering (IINS) spectra showed clearly the existence of a phase transition in d-camphor, which was not observed in dl-borneole. The ND spectra point to a possible cubic structure of the dl-borneole crystal down to helium temperatures. Pressure and temperature dependence of the IINS spectra assumed a glass-like transition from the dynamical to static orientational disorder of molecules in this crystal.

Local structure in beta -Ti1-yVyHx studied by inelastic neutron scattering.

The hydrogen sites in the disordered metal hydrides, \ensuremath{\beta}-${\mathrm{Ti}}_{1\mathrm{\ensuremath{-}}\mathit{y}}$${\mathrm{V}}_{\mathit{y}}$${\mathrm{H}}_{\mathit{x}}$ (x\ensuremath{\sim}1 and 0.2\ensuremath{\le}y\ensuremath{\le}0.9) were studied using the incoherent inelastic neutron scattering (IINS) technique. The IINS spectra of the hydrides were collected at 50 K. Four peaks originated from the \ensuremath{\beta} phase, whose energy ranges were 13 \ensuremath{\le}\ensuremath{\varepsilon}\ensuremath{\le}16 meV, 36 \ensuremath{\le}\ensuremath{\varepsilon}\ensuremath{\le}44 meV, 97\ensuremath{\le}\ensuremath{\varepsilon}\ensuremath{\le}110 meV, and 134\ensuremath{\le}\ensuremath{\varepsilon}\ensuremath{\le}152 meV. These peaks were assigned to the metal lattice vibrations and the local vibrational modes of hydrogen atoms occupying the octahedral site (O site) and two kinds of tetrahedral sites (${\mathit{T}}_{1}$ and ${\mathit{T}}_{2}$ sites), respectively. The ratio of the number of ${\mathit{T}}_{1}$ sites that were observed at the highest energy range to total hydrogen sites decreased and that of the O site increased with increasing V content in the alloy. The composition dependence of the site fraction was analyzed using the cluster model modified to allow short-range ordering of metal atoms. The short-range order parameter was determined to be 0.43\ifmmode\pm\else\textpm\fi{}0.05.

Ion-exchange and protonic species in the antimony hydrogen phosphate HSb(PO4)2·2H2O

It has been established from the incoherent inelastic neutron scattering spectra (IINS) that both the oxonium [H3O]+ and dioxonium [H5O2]+ ions are present in the antimony hydrogen phosphate H1Sb(PO4)2·2H2O, written as H1SbP2·2H2O. However, as the extent of hydration decreases as in H1SbP2·1.25H2O, the proportion of the oxonium [H3O]+ ion increases. MAS NMR indicates that the P—O–H+ group remains undissociated in the anhydrous form. The title compound is an efficient but unselective ion exchanger which is able to extract mono- and poly-valent aquo-cations. In addition, polyvalent complex cations may be exchanged directly without the need for a catalytic or delamination process. A relatively high temperature (266 °C) is needed to dehydrate Co[Sb(PO4)2]2·6H2O in which the cobalt appears to be bound to four water molecules with two axial oxygens from the macroanionic layers.

Comparative neutron scattering study of molecular ordering in d-camphor and dl-borneole

Molecules of both studied substances: d-camphor and dl-borneole are nearly globular in shape and show plastic behaviour at room temperature. Neutron scattering investigations have been performed down to a helium temperature under different hydrostatic pressures up to 400 MPa. Neutron diffraction (ND) and incoherent inelastic neutron scattering (IINS) spectra clearly show the existence of phase transition in d-camphor, which has not been observed in dl-borneole. The ND spectra point to a possible cubic structure of dl-borneole crystal down to helium temperatures; temperature dependence of the IINS spectra suggests continuous transition from dynamical to static disorder of molecules in this crystal.

New electronic transitions observed in the trinuclear iron (III,III,II) cluster, by inelastic neutron scattering

The incoherent inelastic neutron scattering (IINS) spectrum of the iron (III, III, II) complex [Fe 3O(OOCMe) 6(py) 3](py) shows a pair of magnetic transitions at 199 and 221 cm −1. These are assigned to an exchange-coupled doublet, originating from the transition | S, S ab> = | 1, 1 > → | 2, 2 >, which from previous IINS spectra were predicted to occur at 209 cm −1.

Synthesis, characterization and inelastic neutron scattering spectra of hydrogen insertion compounds of the mixed [formula omitted] oxide V 9Mo 6O 40

Hydrogen insertion compounds of V 9Mo 6O 40 have been synthesized and investigated using incoherent inelastic neutron scattering (IINS) vibrational spectroscopy. IINS spectra of H xV 9Mo 6O 40 (x=7.8 and 17.5) confirm that in both phases H is present as coordinated hydroxyl groups. There is no evidence for the presence of coordinated water in contrast to the hydrogen insertion compounds of MoO 3 and V 2O 5.