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Supramolecular interactions are fundamental to host-guest binding in chemical and biological processes. Direct visualisation of such supramolecular interactions within host-guest systems is extremely challenging but crucial for the understanding of their function. We report a comprehensive study combining neutron scattering with synchrotron X-ray and neutron diffraction, coupled with computational modelling, to define the detailed binding at a molecular level of acetylene, ethylene and ethane within the porous host NOTT-300. This study reveals the simultaneous and cooperative hydrogen-bonding, π···π stacking interactions and inter-molecular dipole interactions in the binding of acetylene and ethylene to give up to twelve individual weak supramolecular interactions aligned within the host to form an optimal geometry for intelligent, selective binding of hydrocarbons. We also report, for the first time, the cooperative binding of a mixture of acetylene and ethylene within the porous host together with the corresponding breakthrough experiment and analysis of mixed gas adsorption isotherms.

Polyoligosilsesquioxanes (POSS) are a large family of Si–O cage molecules that have diameters of 1–2 nm and can be viewed as perfectly monodisperse silica nanoparticles. POSS can be synthesized wit...

We present new high-resolution inelastic neutron scattering (INS) spectra (measured using the TOSCA and MARI instruments at ISIS) and powder neutron diffraction data (measured on the diffractometer WISH at ISIS) from the interaction of the prototypical metal–organic framework HKUST-1 with various dosages of dihydrogen gas. The INS spectra show direct evidence for the sequential occupation of various distinct sites for dihydrogen in the metal–organic framework, whose population is adjusted during increasing loading of the guest. The superior resolution of TOSCA reveals subtle features in the spectra, not previously reported, including evidence for split signals, while complementary spectra recorded on MARI present full information in energy and momentum transfer. The analysis of the powder neutron patterns using the Rietveld method shows a consistent picture, allowing the crystallographic indenisation of binding sites for dihydrogen, thus building a comprehensive picture of the interaction of the guest with the nanoporous host.

The dynamics and bonding of the complex hydride LiBH4 have been investigated by vibrational spectroscopy and density functional theory (DFT). The combination of infrared, Raman, and inelastic neutron-scattering (INS) spectroscopies on hydrided and deuterated samples reveals a complete picture of the dynamics of the BH4- ions as well as of the lattice. Particular emphasis is laid on a comparison between experiment and theory, revealing significant discrepancy between the two approaches for vibrations with high anharmonicity, which is related to large vibrational amplitudes. The latter is typical for librational modes in molecular crystals and pseudo-ionic crystals such as complex hydrides. The presented strategy for anharmonic frequency corrections might thus be generally applicable for this kind of materials. © 2013 Elsevier B.V.

Hydrogen has been identified as a fuel of choice for providing clean energy for transport and other applications across the world and the development of materials to store hydrogen efficiently and safely is crucial to this endeavour. Hydrogen has the largest scattering interaction with neutrons of all the elements in the periodic table making neutron scattering ideal for studying hydrogen storage materials. Simultaneous characterisation of the structure and dynamics of these materials during hydrogen uptake is straightforward using neutron scattering techniques. These studies will help us to understand the fundamental properties of hydrogen storage in realistic conditions and hence design new hydrogen storage materials. © 2009 Elsevier Ltd. All rights reserved.

The combination of techniques including switching experiments, temperature programed reduction and in situ neutron scattering-conductivity are used to investigate the sensing mechanism of 1% Pd/SnO 2 toward hydrogen-containing gas mixtures. In particular, the use of the in sim neutron scattering-conductivity for the first time allows the simultaneous monitoring of electrical conductivity and inelastic neutron scattering spectra of the sensor material. Direct evidence is obtained on a reversible migration of hydrogenic species from and to the metal and the underlying tin oxide surface, i.e., reversible hydrogen spillover. As a result of this spillover, a dramatic change in electrical conductivity of the Pd doped tin oxide material is observed. We confirm, in accordance with the known mechanism, that the change of conductivity is based upon the creation or destruction of negatively charged adsorbed oxygen species on the sensor surface. In addition, we report a new but important sensing mechanism, the spillover hydrogen species behaving like a shallow donor to the semiconductor oxide as the direct source of conductivity occurs concurrently with the known mechanism.

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.

Hydrogen bonds dominate many chemical and biological processes, and chemical modification enables control and modulation of host–guest systems. Here we report a targeted modification of hydrogen bonding and its effect on guest binding in redox-active materials. MFM-300(VIII) {[VIII2(OH)2(L)], LH4=biphenyl-3,3′,5,5′-tetracarboxylic acid} can be oxidized to isostructural MFM-300(VIV), [VIV2O2(L)], in which deprotonation of the bridging hydroxyl groups occurs. MFM-300(VIII) shows the second highest CO2 uptake capacity in metal-organic framework materials at 298 K and 1 bar (6.0 mmol g−1) and involves hydrogen bonding between the OH group of the host and the O-donor of CO2, which binds in an end-on manner, =1.863(1) Å. In contrast, CO2-loaded MFM-300(VIV) shows CO2 bound side-on to the oxy group and sandwiched between two phenyl groups involving a unique ···c.g.phenyl interaction [3.069(2), 3.146(3) Å]. The macroscopic packing of CO2 in the pores is directly influenced by these primary binding sites., Gaining molecular-level insight into host–guest binding interactions is fundamentally important, but experimentally challenging. Here, Schröder and co-workers study CO2–host hydrogen bonding interactions in a pair of isostructural redox-active VIII/VIV MOFs using neutron scattering and diffraction techniques.

The production of pure deuterium and the removal of tritium from nuclear waste are the key challenges in separation of light isotopes. Presently, the technological methods are extremely energy- and cost-intensive. Here we report the capture of heavy hydrogen isotopes from hydrogen gas by selective adsorption at Cu(I) sites in a metal-organic framework. At the strongly binding Cu(I) sites (32 kJ mol−1) nuclear quantum effects result in higher adsorption enthalpies of heavier isotopes. The capture mechanism takes place most efficiently at temperatures above 80 K, when an isotope exchange allows the preferential adsorption of heavy isotopologues from the gas phase. Large difference in adsorption enthalpy of 2.5 kJ mol−1 between D2 and H2 results in D2-over-H2 selectivity of 11 at 100 K, to the best of our knowledge the largest value known to date. Combination of thermal desorption spectroscopy, Raman measurements, inelastic neutron scattering and first principles calculations for H2/D2 mixtures allows the prediction of selectivities for tritium-containing isotopologues., Many applications require hydrogen isotopes and so it is important to develop alternative separation technologies. Here, the authors report a metal-organic framework capable of capturing deuterium from H2/D2 mixtures, and go on to predict selectivity for isotopologues containing tritium.

Selective adsorption of SO

A typical type of core-shell polyoxometalates can be obtained through the Keggin-type polyoxometalate-templated growth of a layer of spherical shell structure of {Mo72Fe30}. Small-angle X-ray scattering is used to study the structural features and stability of the core-shell structures in aqueous solutions. Time-resolved small-angle X-ray scattering is applied to monitor the synthetic reactions, and a three-stage formation mechanism is proposed to describe the synthesis of the core-shell polyoxometalates based on the monitoring results. New protocols have been developed by fitting the X-ray data with custom physical models, which provide more convincing, objective, and completed data interpretation. Quasi-elastic and inelastic neutron scattering are used to probe the dynamics of water molecules in the core-shell structures, and two different types of water molecules, the confined and structured water, are observed. These water molecules play an important role in bridging core and shell structures and stabilizing the cluster structures.

We have measured inelastic neutron scattering (INS) spectra from Ti-doped polycrystalline alanates (NaAlH 4 and Na 3 AlH 6 ), at low temperature, in the energy transfer range 3–500 meV, both for thermally treated and untreated samples. From the spectral range corresponding to the fundamental vibrational bands of these aluminohydrides, accurate one-phonon spectra and hydrogen-projected densities of phonon states have been extracted and analyzed using ab initio lattice dynamics calculations. Satisfactory agreement has been found for the untreated samples. In the case of thermally treated samples, due to thermal decomposition, different ionic species are present and the sample composition could be quantitatively evaluated. No evidence for the existence of intermediate species such as AlH 3 or AlH 5 2− has been found.

This study aims at an investigation of the impurity gases emitted during the decomposition of borohydrides. For this we have set up a quantitative gas analysis based on a combination of FTIR spectroscopy and gravimetry. We show that the emission of various intermediates, in particular diborane, depends sensitively on the reaction conditions, including gas mean free path lengths, hydrogen backpressure, and sample pretreatment. Adduct-free Mg(BH 4)2 and LiBH4 emit diborane only at the impurity level, while for LiZn2(BH4)5 diborane is the main decomposition product. The decomposition reaction of LiZn 2(BH4)5 proceeds via a collision-induced dissociation of Zn(BH4)2 in Ar at ambient pressures. Various additives were tested aiming at catalyzing the decomposition of the desorbed diborane. © 2011 American Chemical Society.

Liquid organic hydrides, e.g. 9-ethylcarbazole, are potentially interesting hydrogen storage materials because of their reversible hydrogen sorption properties. In the present work, hydrogenation reaction of 9-ethylcarbazole in the molten form was investigated over a wide variety of noble metal and nickel supported catalysts. The catalytic activity of 8.2 × 10-6 mol-ethylcarbazole/g of metal/s and selectivity of 98% towards a fully hydrogen loaded product were recorded over 5 wt% ruthenium on alumina which was prepared by mild chemical reduction of ruthenium salt. Using this catalyst the theoretical capacity of hydrogen uptake (5.7 wt%) was obtained and the rate of the reaction and activation energy were estimated. Due to its potential high hydrogen storage capacity, this system could be a promising on-board storage candidate for mobile applications. The structures of reaction products and intermediates were identified using 2D NMR techniques. These structures were also predicted to be thermodynamically stable using density functional theory (DFT), matching well with the experimental observations. © 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

Practical methods for hydrogen storage are still a major bottleneck in the realization of an energy economy based on hydrogen as an energy carrier.(1) Surface adsorption within crystalline, nanoporous, metal−organic frameworks (MOFs) provides a promising storage method that relies on sufficiently strong adsorption interactions for a large fraction of the storage capacity. Only few MOF structures were studied up to date using neutron diffraction to resolve the adsorption sites.(2-5) Here we use in situ neutron diffraction to characterize hydrogen (deuterium) adsorption sites in the MOF Cr MIL-53. The strongest adsorption interactions are present at three different sites where the hydrogen touches nearby organic linkers from two directions. Perhaps surprisingly, there is no strong direct interaction with the Cr−O cluster. Large breathing modes of the crystalline lattice are observed upon loading hydrogen reversibly to an equivalent of 5.5 wt %. Such breathing modes are known to occur for polar solvents like...

The dynamics of the hydrogen atoms in the highly ordered kaolinite was studied by vibrational spectroscopy based on inelastic neutron scattering method with the focus on the spectral region of 100–1,250 cm−1. The experimental spectrum was interpreted by means of the solid state density functional theory calculations covering both normal mode analysis and molecular dynamics going beyond the harmonic approximation. The Al–O–H bending modes were found to be spread over the large interval of 100–1,100 cm−1, with the dominant contributions located between 800 and 1,100 cm-1. The shapes of the individual hydrogen spectra depend on the strengths of the individual interlayer O–H···O hydrogen bonds involving the inner surface hydroxyl groups. The modes assigned to the in-plane movements of the respective hydrogen atoms are well-defined and always appear on the top of the intervals of energy transfer. In contrast, the modes generated by the out-of-plane movements are spread over large intervals of energies spanning down to the region of external (lattice) modes.

Raman spectra of Mg(BH(4))(2) have been measured in an extensive temperature range, from 15 to 473 K. Taking into account the high temperature conversion from the alpha to the beta phase, we have observed evident signatures of this phase transition and determined the Raman vibrational spectrum of each phase. The neutron scattering spectra of the beta phase sample were also recorded. The present experimental results have been compared to the density functional theory calculations available in the literature, and a substantial agreement has been found.

In the present article the effect of kosmotrope compounds, i.e. systems having the capability to stabilize biological macromolecules, is investigated by using complementary techniques. The attention is focused on the kosmotrope character of trehalose, a glucose disaccharide, compared to its homologous maltose and sucrose. Complementary techniques of neutron scattering, such as Inelastic Neutron Scattering (INS) and Quasi Elastic Neutron Scattering (QENS) allow to point out the capability of trehalose to strongly affect both the structural and dynamical properties of water. Finally the stabilization effect of trehalose on a well know protein, lysozyme, is studied as a function of temperature by Small Angle Neutron Scattering (SANS).

Employing femtosecond IR pump-probe and 2D spectroscopy, we measure the vibrational dynamics of LiBH(4) and several of its deuterium isotopomers. We find that the vibrational lifetime of various BH and BD stretching modes uniformly is approximately 1.5 ps for all BH(4-x)D(x)(-) units (0or=xor=4). Subsequently, vibrational energy cascades down through BH and BD bending, facilitated by a strong Fermi resonance, into external (librational and translational) modes with a 3 ps time constant. Final thermalization of the energy is completed in about 100 ps. The vibrational spectra are purely homogeneously broadened indicating low inhomogeneity due to static disorder. We furthermore measured the anharmonic constants of various modes, which sets the benchmark for future ab initio calculations, and completed the first FTIR assignment of the stretching vibrations for the five BH(4-x)D(x)(-) units.

The metal-organic framework, MIL-53, can have a structural transition from an open-pored to a closed-pored structure by adsorbing different guest molecules. The aid of guest molecules is believed to be necessary to initiate this "breathing" effect. Using both neutron powder diffraction and inelastic neutron scattering techniques, we find that MIL-53 exhibits a reversible structural transition between an open-pored and a closed-pored structure as a function of temperature without the presence of any guest molecules. Surprisingly, this structural transition shows a significant temperature hysteresis: the transition from the open-pored to closed-pored structure occurs at approximately 125 to 150 K, while the transition from the closed-pored to open-pored structure occurs around 325 to 375 K. To our knowledge, this is first observation of such a large temperature hysteresis of a structural transition in metal-organic frameworks. We also note that the transition from the open to closed structure at low temperature shows very slow kinetics. An ab initio computer simulation is employed to investigate the possible mechanism of the transition.

Hydrogen adsorption in porous, high surface area, and stable metal organic frameworks (MOF’s) appears a novel route towards hydrogen storage materials [N.L. Rosi, J. Eckert, M. Eddaoudi, D.T. Vodak, J. Kim, M. O’Keeffe, O.M. Yaghi, Science 300 (2003) 1127; J.L.C. Rowsell, A.R. Millward, K. Sung Park, O.M. Yaghi, J. Am. Chem. Soc. 126 (2004) 5666; G. Ferey, M. Latroche, C. Serre, F. Millange, T. Loiseau, A. Percheron-Guegan, Chem. Commun. (2003) 2976; T. Loiseau, C. Serre, C. Huguenard, G. Fink, F. Taulelle, M. Henry, T. Bataille, G. Ferey, Chem. Eur. J. 10 (2004) 1373]. A prerequisite for such materials is sufficient adsorption interaction strength for hydrogen adsorbed on the adsorption sites of the material because this facilitates successful operation under moderate temperature and pressure conditions. Here we report detailed information on the geometry of the hydrogen adsorption sites, based on the analysis of inelastic neutron spectroscopy (INS). The adsorption energies for the metal organic framework MOF5 equal about 800 K for part of the different sites, which is significantly higher than for nanoporous carbon materials (∼550 K) [H.G. Schimmel, G.J. Kearley, M.G. Nijkamp, C.T. Visser, K.P. de Jong, F.M. Mulder, Chem. Eur. J. 9 (2003) 4764], and is in agreement with what is found in first principles calculations [T. Sagara, J. Klassen, E. Ganz, J. Chem. Phys. 121 (2004) 12543; F.M. Mulder, T.J. Dingemans, M. Wagemaker, G.J. Kearley, Chem. Phys. 317 (2005) 113]. Assignments of the INS spectra is realized using comparison with independently published model calculations [F.M. Mulder, T.J. Dingemans, M. Wagemaker, G.J. Kearley, Chem. Phys. 317 (2005) 113] and structural data [T. Yildirim, M.R. Hartman, Phys. Rev. Lett. 95 (2005) 215504].

We report an inelastic neutron scattering (INS) study of a monosaccharide, 1,6-anhydro-β- d -glucopyranose, C 6 O 5 H 10 (levoglucosan). The assignment of the experimental vibrational spectrum measured in the range 30–4000 cm −1 on TOSCA spectrometer has been made by means of DFT calculations. To simulate crystal environment both molecular cluster and periodic models were used. The INS spectrum calculated with the periodic model is a better fit of the experiment than the cluster model. On the other hand the peaks between 630 and 730 cm −1 in the experimental INS assigned to OH torsional modes were reproduced better by the cluster calculations. The study has been completed by an alternative approach, molecular dynamics (MD) calculations, done at the same level of the DFT theory. The simulation trajectories were analyzed in both time and frequency space to determine the dynamical contributions to the observed spectra. Comparing the positions of the peaks in the power spectra and in the INS spectra, the former gave a better fit of the experimental ones in all the frequency ranges when compared to the spectra based on dynamical matrix. Our calculations, in general, underestimated the frequencies of the modes in the region between 500 and 1500 cm −1 by maximum of 30 cm −1 . The power spectra of the velocity autocorrelation function for centre of mass of a molecule of levoglucosan show peaks below 160 cm −1 .

The gate-opening phenomenon in ZIFs is of paramount importance to understand their behavior in industrial molecular separations. Here we show for the first time using in situ inelastic neutron scattering (INS) the swinging of the –CH3 groups and the imidazolate linkers in the prototypical ZIF-8 and ZIF-8@AC hybrid materials upon exposure to mild N2 pressure. The authors acknowledge financial support from MINECO projects: MAT2013-45008-p and CONCERT Project-NASEMS (PCIN-2013-057). EVRF gratefully acknowledge support from MINECO (Spain) for his Ramón y Cajal grant (RyC-2012-11427). DFJ thanks the Royal Society (UK) for funding through a University Research Fellowship and Dr Axel Zeitler for interesting discussions. This research benefited from the use of the VISION beamline (IPTS-13608) at ONRL’s Spallation Neutron Source and the VirtuES (Virtual Experiments in Spectroscopy) project, (LDRD 7739), which are supported by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy, under Contract No. DE-AC0500OR22725 with UT Battelle, LLC.

We report an inelastic neutron scattering (INS) study of the rotational–vibrational spectrum of dihydrogen sorbed by zeolite CaX. In the low energy (

It is well known that water plays a fundamental role for living beings, because the nature of water transformations provides for the ability to preserve biostructures. Solute can be classified as “kosmotropes” or “chaotropes” depending on the interaction strength with water. In the case of solutes destroying the natural hydrogen bonded network of water, called “kosmotropes” or “structure-makers”, the denaturation processes can be inhibited. The aim of this work is to investigate the vibrational behaviour of maltose/H 2 O mixtures in order to characterise the changes induced by the sugar on the H 2 O hydrogen-bonded network. The obtained findings point out that maltose has a destructuring effect on the water tetrahedral network and emphasise its kosmotrope character.

Currently microporous oxidic materials including zeolites are attracting interest as potential hydrogen storage materials. Understanding how molecular hydrogen interacts with these materials is important in the rational development of hydrogen storage materials and is also challenging theoretically. In this paper, we present an incoherent inelastic neutron scattering (INS) study of the adsorption of molecular hydrogen and hydrogen deuteride (HD) in a copper substituted ZSM5 zeolite varying the hydrogen dosage and temperature. We have demonstrated how inelastic neutron scattering can help us understand the interaction of H 2 molecules with a binding site in a particular microporous material, Cu ZSM5, and by implication of other similar materials. The H 2 molecule is bound as a single species lying parallel with the surface. As H 2 dosing increases, lateral interactions between the adsorbed H 2 molecules become apparent. With rising temperature of measurement up to 70 K (the limit of our experiments), H 2 molecules remain bound to the surface equivalent to a liquid or solid H 2 phase. The implication is that hydrogen is bound rather strongly in Cu ZSM5. Using the simple model for the anisotropic interaction to calculate the energy levels splitting, we found that the measured rotational constant of the hydrogen molecule is reduced as a consequence of adsorption by the Cu ZSM5. From the decrease in total signal intensity with increasing temperature, we were able to observe the conversion of para -hydrogen into ortho -hydrogen at paramagnetic centres and so determine the fraction of paramagnetic sites occupied by hydrogen molecules, ca. 60%.

An inelastic neutron scattering (INS) study of the rotational–vibrational spectrum of dihydrogen sorbed by zeolite X having substituted sodium, calcium and zinc cations is reported. The rotational–vibrational spectrum of H2 was observed at low energy transfer (below ca. 25 meV, 202 cm−1); the vibration was that of the H2 molecule against the binding site (H2–X, not H–H). The vibration frequency was proportional to the polarising power of the cation (Na+ < Ca2+ < Zn2+). Polarisation of the H2 molecule dominated the interaction of H2 with this binding site. The total scattering intensity was proportional to the dihydrogen dose. However the vibrational intensities became constant at ca. 0.3 wt% showing that the H2 binding sites had saturated. Additional dihydrogen appeared as unbound or weakly bound dihydrogen exhibiting recoil.

Natural methane hydrates are believed to be the largest source of hydrocarbons on Earth. These structures are formed in specific locations such as deep-sea sediments and the permafrost based on demanding conditions of high pressure and low temperature. Here we report that, by taking advantage of the confinement effects on nanopore space, synthetic methane hydrates grow under mild conditions (3.5 MPa and 2 degrees C), with faster kinetics (within minutes) than nature, fully reversibly and with a nominal stoichiometry that mimics nature. The formation of the hydrate structures in nanospace and their similarity to natural hydrates is confirmed using inelastic neutron scattering experiments and synchrotron X-ray powder diffraction. These findings may be a step towards the application of a smart synthesis of methane hydrates in energy-demanding applications (for example, transportation)., We acknowledge UK Science and Technlology Facilities Council for the provision of beam time on the TOSCA spectrometer (Projects RB1410624 and RB122099) and financial support from the European Commission under the 7th Framework Programme through the 'Research Infrastructures' action of the 'Capacities' Programme (NMI3-II Grant number 283883). J.S.-A. and F.R. acknowledges the financial support from MINECO: Strategic Japanese-Spanish Cooperation Program (PLE2009-0052), Concert Project-NASEMS (PCIN-2013-057) and Generalitat Valenciana (PROMETEO/2009/002). F.R. and J.L.J. thank the financial support from MINECO (MAT2012-38567-C02-01, Consolider Ingenio 2010-Multicat CSD-2009-00050 and SEV-2012-0267). K.K. thanks Grant-in-Aid for Scientific Research (A) (2424-1038), Japan. A.B. and A.U. thank the financial support from MINECO (SEV-2013-0319). J.L.J. and I.P. thank synchrotron ALBA for beamtime availability.

We use density-functional theory molecular dynamics (DFT-MD) simulations to determine the hydride transfer coordinate between palladium centres of the crystallographically observed terminal hydride locations, Pd–Pd–H, originally postulated for the solution dynamics of the complex bis-NHC dipalladium hydride [{(MesIm)2CH2}2Pd2H][PF6], and then calculate the free-energy along this coordinate. We estimate the transfer barrier-height to be about 20 kcal mol−1 with a hydride transfer rate in the order of seconds at room temperature. We validate our DFT-MD modelling using inelastic neutron scattering which reveals anharmonicity of the hydride environment that is so pronounced that there is complete failure of the harmonic model for the hydride ligand. The simulations are extended to high temperature to bring the H-transfer to a rate that is accessible to the simulation technique.

We have measured Incoherent Inelastic Neutron Scattering (IINS) spectra of H2 physisorbed in high purity chemically activated carbon (AC) at different surface coverage and at temperatures near the triple point of bulk hydrogen. Our experimental results and DFT calculations show that at low surface coverage, due to the very low corrugation of the adsorption potential, and in the absence of H2–H2 lateral interactions, the adsorbed molecules are practically free to translate in the 2D plane parallel to the surface. Model calculations show that a complete mixing between the sub-states of the J = 1 manifold occurs on the free surface. The J = 0-to-1 rotational transition should split if the H2 molecule is adsorbed in a slit type pore. Rotational splitting of up to 13 meV is found in the narrowest pores of around 6 A investigated. The calculated isosteric heat of adsorption for molecules adsorbed on the free surface, at different sites and molecule orientations, range between −39 and −42 meV/H2 at 77 K. In the optimum size slit pores, these numbers double up. Micropore volume of 0.34–0.45 ml/g carbon, and an upper limit of 4 wt% hydrogen storage is anticipated for the investigated material.

Neutron scattering has been demonstrated to be a powerful tool for characterizing the structure and dynamics of biological molecules and for investigating the physical and chemical mechanisms of biophysical processes. The aim of the present work is to investigate by inelastic neutron scattering (INS) the vibrational behaviour of a class of bioprotectant systems, such as homologous disaccharides, trehalose, maltose and sucrose, in water mixtures. INS measurements have been performed on trehalose/H 2 O, maltose/H 2 O and sucrose/H 2 O mixtures at very low temperature as a function of concentration by using the thermal original spectrometer with cylindrical analyzers (TOSCA) spectrometer at the ISIS Facility (DRAL, UK). The findings allow the analyses of the vibrational features of the INS spectra in order to study the effect of disaccharides on the H 2 O hydrogen-bonded tetrahedral network. The obtained neutron scattering findings point out that disaccharides, and in particular trehalose, have a destructuring effect on the water tetrahedral network, as emphasized by the analysis of the librational modes region from 50 to 130 meV energy transfer. On the other hand, the analysis of the bending modes region (130–225 meV) shows a locally ordered structure in the disaccharide/H 2 O mixtures. Finally, the observed experimental evidences are linked to the different bioprotective effectiveness of disaccharides as a function of concentration.

In a previous work, we carried out inelastic neutron scattering (INS) spectroscopy experiments and preliminary first principles calculations on alkali metal hydrides. The complete series of alkali metal hydrides, LiH, NaH, KH, RbH and CsH was measured in the high-resolution TOSCA INS spectrometer at ISIS. Here, we present the results of ab initio electronic structure calculations of the properties of the alkali metal hydrides using both the local density approximation (LDA) and the generalized gradient approximation (GGA), using the Perdew–Burke–Ernzerhof (PBE) parameterization. Properties calculated were lattice parameters, bulk moduli, dielectric constants, effective charges, electronic densities and inelastic neutron scattering (INS) spectra. We took advantage of the currently available computer power to use full lattice dynamics theory to calculate thermodynamic properties for these materials. For the alkali metal hydrides (LiH, NaH, KH, RbH and CsH) using lattice dynamics, we found that the INS spectra calculated using LDA agreed better with the experimental data than the spectra calculated using GGA. Both zero-point effects and thermal contributions to free energies had an important effect on INS and several thermodynamic properties. Fil: Barrera, Gustavo Daniel. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Rutherford Appleton Laboratory; Reino Unido Fil: Colognesi, D.. Istituto dei Sistemi Complessi; Italia Fil: Mitchell, P. C. H.. University of Reading; Reino Unido Fil: Ramirez Cuesta, A. J.. University of Reading; Reino Unido. Rutherford Appleton Laboratory; Reino Unido

Ball milled magnesium hydride with an average size of about 40 nm and bulk magnesium hydride have been studied with vibrational spectroscopy together with density functional computer calculations. Using this combination of techniques structural information can now be obtained on a nanometer scale, which is especially important for nanosized samples. Such samples exhibit very broad diffraction lines, from which limited information about the structure can be extracted. It was found that ball milling distorts the vibrational spectra due to distribution in stresses over the sample. Cycling of the hydrogen content of ball milled samples results in the spectrum of unmilled samples, while the particle size remains small and hydrogen storage characteristics continue to be better for ball milled samples. We conclude that improved performance for hydrogen storage applications of ball milled magnesium hydride has to be attributed to the reduction of the particle size, while defect densities inside the particles play less of a role.

Differential scanning calorimetry of the hydrated, microporous aluminum phosphate AlPO-14 shows two distinct water losses between room temperature and 120 degrees C, indicating the presence of two types of water in the solid. Multiple-quantum magic angle spinning (MQMAS) (27)Al NMR shows that, while in dehydrated AlPO-14 all aluminum is found in tetrahedral sites, on hydration a significant proportion of the aluminum increases its coordination number to 6. This accounts for the presence of tightly bound water. The first detailed incoherent inelastic neutron scattering (IINS) studies of such a system give a spectrum with distinct and sharp librational bands for bound water, significantly different than seen in ice Ih. Using these data, and by consideration of the crystal structure of dehydrated AlPO-14, we propose a model for the hydrated material in which the tightly bound water bridges pairs of Lewis acidic framework aluminums in a dense region of the structure, while loosely bound water resides in the pores of the solid. Further IINS measurements using a high-incident neutron energy provide data that are in agreement with our model. We can detect two O-H stretching modes for bound water in hydrated AlPO-14, consistent with the model of two types of water present in the material, with the loosely bound water connected to neighboring water molecules by intermolecular hydrogen bonds.

Inelastic neutron scattering (INS) spectra were measured in situ from progressively increased amounts of para-hydrogen physisorbed in bundles of single-walled carbon nanotubes at temperatures in the vicinity of 20 K. INS from the bound H2 molecules consists of two distinct parts carrying complementary information. In the low energy and momentum transfer region, at about 14.5 meV we observe a sharp line corresponding to rotational transitions between the ground para-J = 0 state and the ground ortho-J = 1 state without change of the translational state of the molecular centre of mass (CoM). This we call the ''bound'' spectrum. At higher energy transfers, a series of broad peaks are observed, corresponding to rotational transitions between the para-J = 0 state and different ortho-states (J = 1,3,5, . . . ,) shifted out in energy transfer by an amount equal to the CoM recoil energy. This we call the ''recoil'' spectrum. Both parts of each spectrum are analysed using the Young and Koppel model. From the ''bound'' spectrum we estimate the mean height of the barrier to rotation and the mean square displacements of the molecules accommodated at different adsorption sites. The ''recoil'' spectrum allows us to derive the mean translational kinetic energy of the adsorbed hydrogen as a function of the surface concentration.

Molecular crowding has been shown to be important in many cellular processes. The crowded environment in the cell results in a significant proportion of the cellular water being in contact with macromolecules such as proteins and DNA. These interfacial water molecules show a reduced dynamic motion that has been observed with isolated macromolecules using several biophysical techniques. Previously we investigated the inelastic neutron scattering properties of water closely associated with isolated biomolecules, and showed that interfacial water is strongly perturbed, as judged by its energy transfer spectrum. Here we have probed living cells using inelastic and quasielastic neutron scattering. We have found that mild heat stress ('heat shock'), which causes some proteins to become unfolded in the cell, results in changes in the inelastic neutron scattering in the librational region (45-130 meV). Heat shock also causes a narrowing of the quasielastic scattering peak. These changes can be understood in terms of an increase in the proportion of interfacial water molecules, and a net reduction in proton dynamics.

Inelastic neutron scattering spectra from polycrystalline NaH, KH, RbH and CsH, measured at low temperature in the energy transfer range 3 meV < E < 500 meV, are reported. From the medium-energy regions, coinciding with the optical phonon bands, accurate hydrogen-projected densities of phonon states are extracted and compared to ab initio lattice dynamics results. The overall agreement is very good. Further lattice dynamics calculations, based on a pairwise Born–Mayer semi-empirical potential scheme, were also performed, providing only limited and qualitative agreement with the experimental data. In conclusion, incoherent inelastic neutron spectroscopy proves to be a stringent validation tool for lattice dynamics simulations of H-containing materials. Fil: Auffermann, G.. Max Planck Institut fur Chemische Physik fester Stoffe; Alemania Fil: Barrera, Gustavo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco". Facultad de Ciencias Naturales - Sede Comodoro. Departamento de Química; Argentina Fil: Colognesi, D.. Istituto di Fisica Applicata ‘Nello Carrara’. Consiglio Nazionale delle Ricerche; Italia Fil: Corradi, G.. Istituto di Fisica Applicata ‘Nello Carrara’. Consiglio Nazionale delle Ricerche; Italia Fil: Ramirez Cuesta, A. J.. Rutherford Appleton Laboratory; Reino Unido Fil: Zoppi, M.. Istituto di Fisica Applicata ‘Nello Carrara’. Consiglio Nazionale delle Ricerche; Italia

In Inelastic Neutron Scattering Spectroscopy , the neutron scattering intensity is plotted versus neutron energy loss giving a spectrum that looks like an infrared or a Raman spectrum . Unlike IR or Raman, INS does not have selection rules, i.e. all transitions are in principle observable. This particular characteristic makes INS a test bed for Density Functional Theory calculations of vibrational modes . aCLIMAX is the first user friendly program, within the Windows environment, that uses the output of normal modes to generate the calculated INS of the model molecule, making a lot easier to establish a connection between theory and experiment. Program summary Title of program: aCLIMAX 4.0.1 Catalogue identifier: ADSW Program summary URL: http://cpc.cs.qub.ac.uk/summaries/ADSW Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Operating systems: Windows 95 onwards, except Windows ME where it does not work Programming language used: Visual Basic Memory requirements: 64 MB No. of processors: 1 Has the code been parallelized: No No. of bytes in distributed program, including test data, etc.: 2 432 775 No. of lines in distributed program, including test data, etc.: 17 998 Distribution format: tar gzip file Nature of physical problem: Calculation of the Inelastic Neutron Scattering Spectra from DFT calculations of the vibrational density of states for molecules. Method of solution: INS spectral intensity calculated from normal modes analysis. Isolated molecule approximation. Typical time of running: From few seconds to few minutes depending on the size of the molecule. Unusual features of the program: Special care has to be taken in the case of computers that have different regional options than the English speaking countries, the decimal separator has to be set as “.” (dot) instead of the usual “,” (comma) that most countries use.

Neutron inelastic scattering spectra from high quality single-wall carbon nanotubes (SWNTs), progressively dosed with hydrogen, have been measured with high resolution at different temperatures in the vicinity of 20 K. The spectra consist of two parts. Firstly, a relatively sharp complex peak, due to scattering from translationally bound molecules undergoing rotational transitions, is observed at around 14.5 meV. Secondly, there is a series of broad features at higher energies originating from roto-vibrational transitions corresponding to J = 0 to 1 rotational change plus n = 0 to n = 1, 2, etc molecular centre-of-mass vibrational transitions, as well as from molecule centre-of-mass recoil. The structure of the complex sharp peak suggests that the molecular hydrogen is adsorbed on at least two different adsorption sites on the surfaces of the nanotube bundles.

Hydrogen spillover on carbon-supported precious metal catalysts has been investigated with inelastic neutron scattering (INS) spectroscopy. The aim, which was fully realized, was to identify spillover hydrogen on the carbon support. The inelastic neutron scattering spectra of Pt/C, Ru/C, and PtRu/C fuel cell catalysts dosed with hydrogen were determined in two sets of experiments: with the catalyst in the neutron beam and, using an annular cell, with carbon in the beam and catalyst pellets at the edge of the cell excluded from the beam. The vibrational modes observed in the INS spectra were assigned with reference to the INS of a polycyclic aromatic hydrocarbon, coronene, taken as a molecular model of a graphite layer, and with the aid of computational modeling. Two forms of spillover hydrogen were identified: H at edge sites of a graphite layer (formed after ambient dissociative chemisorption of H-2), and a weakly bound layer of mobile H atoms (formed by surface diffusion of H atoms after dissociative chernisorption of H-2 at 500 K). The INS spectra exhibited characteristic riding modes of H on carbon and on Pt or Ru. In these riding modes H atoms move in phase with vibrations of the carbon and metal lattices. The lattice modes are amplified by neutron scattering from the H atoms attached to lattice atoms. Uptake of hydrogen, and spillover, was greater for the Ru containing catalysts than for the Pt/C catalyst. The INS experiments have thus directly demonstrated H spillover to the carbon support of these metal catalysts.

Inelastic neutron scattering spectroscopy has been used to observe and characterise hydrogen on the carbon component of a Pt/C catalyst. INS provides the complete vibration spectrum of coronene, regarded as a molecular model of a graphite layer. The vibrational modes are assigned with the aid of ab initio density functional theory calculations and the INS spectra by the a-CLIMAX program. A spectrum for which the H modes of coronene have been computationally suppressed, a carbon-only coronene spectrum, is a better representation of the spectrum of a graphite layer than is coronene itself. Dihydrogen dosing of a Pt/C catalyst caused amplification of the surface modes of carbon, an effect described as H riding on carbon. From the enhancement of the low energy carbon modes (100–600 cm−1) it is concluded that spillover hydrogen becomes attached to dangling bonds at the edges of graphitic regions of the carbon support.

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.

The location of hydrogen within Ti–Cr–V–Mo alloys has been investigated during hydrogen absorption and desorption using in situ neutron powder diffraction and inelastic neutron scattering. Neutron powder diffraction identifies a low hydrogen equilibration pressure body-centred tetragonal phase that undergoes a martensitic phase transition to a face-centred cubic phase at high hydrogen equilibration pressures. The average location of the hydrogen in each phase has been identified from the neutron powder diffraction data although inelastic neutron scattering combined with density functional theory calculations show that the local structure is more complex than it appears from the average structure. Furthermore the origin of the change in dissociation pressure and hydrogen trapping on cycling in Ti–Cr–V–Mo alloys is discussed.

Mesoporous binary Al x Ni y and ternary Al x Ni y Fe z Raney-type catalysts were synthesised by a two-step procedure involving two main processes, i.e. (i) mechanical metal alloying and (ii) alkaline aluminium leaching. Pure metallic powders of Al, Ni and Fe (if required) were first mechanically alloyed in an attrition mill and then subjected to KOH leaching to selectively remove part of the aluminium atoms. After a slow drying process, a fine, nanostructured slit-shaped material was obtained. Substrate characterisation involved studies by atomic absorption (AA), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDXS) in the SEM and nitrogen physisorption. An intermetallic β- or B2-(AlNi) phase with a metastable bcc crystalline structure was formed as a non-equilibrium phase after the metal alloying process. Because of aluminium removal, the β-(AlNi) phase was transformed into the more stable nickel fcc structure. In this work, some important physico-chemical properties of binary (Al–Ni) and ternary (Al–Ni–Fe) catalysts, with especial attention to textural properties adduced from nitrogen physisorption, are presented and discussed.

We have carried out a comprehensive characterization of the structure and dynamics of maleic anhydride using experimental (single-crystal neutron diffraction, infrared, Raman and inelastic neutron scattering (INS) spectroscopies) and computational methods (AM1 and two levels of density functional theory). The structure is largely in agreement with previous work, although with more accurate atomic positions. However, the report of an unusually short CC bond length is not supported by this work. The combination of ab initio results and INS spectra has confirmed the assignments of the internal modes. In addition, the complete lattice mode region is observed and assigned for the first time. Force fields derived by empirical means and from the ab initio data have been obtained and show differences, although both accurately predict the INS spectrum.

The interaction of CO 2 with a polycrystalline molybdenum-foil (Mo-foil) was previously studied at 77 K through mass-resolved flash thermal desorption spectroscopy (FTDS). From the results, a statistical model was developed with two kinds of sites (bridge and hollow type), CO 2 can adsorb on both but dissociates only on hollow ones. The proposed model reproduces the evolution of desorption peak areas as a function of CO 2 exposure without using any fitting parameter. Because of the sample polycrystallinity, all desorption peaks were fitted assuming a Gaussian distribution of desorption energies with a pre-exponential factor of 10 13 . Values of ∼60.6, ∼126.9 and ∼158.7 kJ/mol were obtained for the desorption energies of CO 2 from α 1 , β 1 and γ 1 states, respectively, while 73.1 and 110.6 kJ/mol correspond to the CO α 2 and β 2 desorption peaks.

Here we show, by in situ scanning tunnelling microscopy, that Pd nanoparticles enhance the rate of re-oxidation of a sub-stoichiometric TiO2(1 1 0) surface. We believe that O2 dissociatively adsorbs at 673 K on the Pd, and “spills over” onto the support where further reaction takes place. Tin+ interstitial ions in the bulk crystal lattice react with the spillover oxygen at the surface, preferentially growing TiO2 around and over the particles. We employ a kinetic Monte-Carlo scheme to simulate this surface reaction and find a good correlation between the simulation and STM images. The simulation indicates that the surface structure may be reproduced in a model in which mobile species spillover from the metal particle, performs a random walk until it reaches a step edge where it may react (with low probability) to form TiO2. The mobile species may also down-step to a lower terrace but up-stepping is forbidden. The temporal evolution of surface structures from both experiment and simulation are compared.