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A J Horsewill - One of the best experts on this subject based on the ideXlab platform.
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the endofullerene hf c60 Inelastic Neutron Scattering spectra from quantum simulations and experiment validity of the selection rule and symmetry breaking
Journal of Physical Chemistry Letters, 2019Co-Authors: Peter M Felker, A J Horsewill, S Rols, Salvatore Mamone, Richard J Whitby, Zlatko BacicAbstract:Accurate quantum simulations of the low-temperature Inelastic Neutron Scattering (INS) spectra of HF@C60 are reported for two incident Neutron wavelengths. They are distinguished by the rigorous in...
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experimental theoretical and computational investigation of the Inelastic Neutron Scattering spectrum of a homonuclear diatomic molecule in a nearly spherical trap h2 c60
Physical Chemistry Chemical Physics, 2016Co-Authors: Salvatore Mamone, Mark R Johnson, S Rols, Monica Jimenezruiz, A J HorsewillAbstract:In this paper we report a methodology for calculating the Inelastic Neutron Scattering spectrum of homonuclear diatomic molecules confined within nano-cavities of spherical symmetry. The method is based on the expansion of the confining potential into multipoles of the coupled rotational and translational angular variables. The Hamiltonian and the INS transition probabilities are evaluated analytically. The method affords a fast and computationally inexpensive way to simulate the Inelastic Neutron Scattering spectrum of molecular hydrogen confined in fullerene cages. The potential energy surface is effectively parametrized in terms of few physical parameters comprising an harmonic term, anharmonic corrections and translation–rotation couplings. The parameters are refined by matching the simulations against the experiments and the excitation modes are identified for transfer energies up to 215 meV.
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confirming a predicted selection rule in Inelastic Neutron Scattering spectroscopy the quantum translator rotator h2 entrapped inside c60
Physical Review Letters, 2014Co-Authors: Monica Jimenezruiz, S Rols, Mark R Johnson, Marina Carravetta, Zlatko Bacic, Mark Denning, Xuegong Lei, A J HorsewillAbstract:We report an Inelastic Neutron Scattering (INS) study of H2 molecule encapsulated inside the fullerene C60 which confirms the recently predicted selection rule, the first to be established for the INS spectroscopy of aperiodic, discrete molecular compounds. Several transitions from the ground state of para-H2 to certain excited translation-rotation states, forbidden according to the selection rule, are systematically absent from the INS spectra, thus validating the selection rule with a high degree of confidence. Its confirmation sets a precedent, as it runs counter to the widely held view that the INS spectroscopy of molecular compounds is not subject to any selection rules.
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quantum rotation and translation of hydrogen molecules encapsulated inside c60 temperature dependence of Inelastic Neutron Scattering spectra
Philosophical Transactions of the Royal Society A, 2013Co-Authors: A J Horsewill, Yasujiro Murata, Kelvin S K Goh, S Rols, Jacques Ollivier, Mark R Johnson, Malcolm H Levitt, Marina Carravetta, Salvatore Mamone, Judy Y C ChenAbstract:The quantum dynamics of a hydrogen molecule encapsulated inside the cage of a C60 fullerene molecule is investigated using Inelastic Neutron Scattering (INS). The emphasis is on the temperature dep...
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Quantum Translator-Rotator: Inelastic Neutron Scattering of Dihydrogen Molecules Trapped inside Anisotropic Fullerene Cages
Physical review letters, 2009Co-Authors: A J Horsewill, Yasujiro Murata, S Rols, Mark R Johnson, Salvatore Mamone, K. S. Panesar, Koichi Komatsu, A. Danquigny, F. Cuda, S. MaltsevAbstract:We report an Inelastic Neutron Scattering investigation of the quantum dynamics of hydrogen molecules trapped inside anisotropic fullerene cages. Transitions among the manifold of quantized rotational and translational states are directly observed. The spectra recorded as a function of energy and momentum transfer are interpreted in terms of the rotational potential and the cage dimensions. The thermodynamics of orthohydrogen and parahydrogen are investigated through temperature dependence measurements.
Stewart F. Parker - One of the best experts on this subject based on the ideXlab platform.
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investigation of zsm 5 catalysts for dimethylether conversion using Inelastic Neutron Scattering
Applied Catalysis A-general, 2019Co-Authors: Stewart F. Parker, Andrea Zachariou, Alexander P Hawkins, David Lennon, Santhosh Kumar Matam, Richard C A CatlowAbstract:We report the characterisation of zeolite ZSM-5 catalysts used in the conversion of dimethylether to hydrocarbons. Inelastic Neutron Scattering spectroscopy, supported by solid state NMR, shows that the more rapid deactivation occurring with dimethylether compared with methanol is associated with the formation of less methylated aromatic coke species and attributed to the lower levels of water present during dimethylether conversion. The ability of Inelastic Neutron Scattering to probe a working catalyst with no sample preparation is demonstrated.
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application of Inelastic Neutron Scattering to the methanol to gasoline reaction over a zsm 5 catalyst
Catalysis Letters, 2016Co-Authors: Russell F Howe, Stewart F. Parker, James Mcgregor, Paul Collier, David LennonAbstract:Inelastic Neutron Scattering (INS) is used to investigate a ZSM-5 catalyst that has been exposed to methanol vapour at elevated temperature. In-line mass spectrometric analysis of the catalyst exit stream confirms methanol-to-gasoline chemistry, whilst ex situ INS measurements detect hydrocarbon species formed in/on the catalyst during methanol conversion. These preliminary studies demonstrate the capability of INS to complement infrared spectroscopic characterisation of the hydrocarbon pool present in/on ZSM-5 during the MTG reaction.
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Inelastic Neutron Scattering studies of methyl chloride synthesis over alumina
Accounts of Chemical Research, 2014Co-Authors: David Lennon, Stewart F. ParkerAbstract:Not only is alumina the most widely used catalyst support material in the world, it is also an important catalyst in its own right. One major chemical process that uses alumina in this respect is the industrial production of methyl chloride. This is a large scale process (650 000 metric tons in 2010 in the United States), and a key feedstock in the production of silicones that are widely used as household sealants. In this Account, we show how, in partnership with conventional spectroscopic and reaction testing methods, Inelastic Neutron Scattering (INS) spectroscopy can provide additional insight into the active sites present on the catalyst, as well as the intermediates present on the catalyst surface.INS spectroscopy is a form of vibrational spectroscopy, where the spectral features are dominated by modes involving hydrogen. Because of this, most materials including alumina are largely transparent to Neutrons. Advantageously, in this technique, the entire “mid-infrared”, 0–4000 cm–1, range is accessibl...
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Inelastic Neutron Scattering and raman spectroscopies and periodic dft studies of rb2pth6 and rb2ptd6
ChemInform, 2003Co-Authors: Stewart F. Parker, Anibal J Ramirezcuesta, Stephen M Bennington, Gudrun Auffermann, Welf Bronger, Henryk Herman, Kenneth P J Williams, Tim SmithAbstract:The present work has provided a complete set of assignments for the vibrational spectrum of Rb2PtH6 and Rb2PtD6. To confirm the assignments, a periodic density functional theory (DFT) code has been applied to the analysis of the Inelastic Neutron Scattering (INS) spectrum of an ionic material for the first time. The work has also provided an explanation for the unusual infrared spectrum of the potassium salt. The most significant aspect of the work is the use of the momentum transfer information provided by an INS chopper spectrometer. The straightforward method employed for the analysis of the data is applicable to any molecular system (organic or inorganic) and demonstrates the potential of these instruments for chemistry. Periodic DFT was also used to study the other A2PtH6 (A = alkali metal) including, the at present, unknown Li salt, which is found to be stable. The DFT studies have also highlighted the crucial role of the cation in removing charge from the transition metal and “hydride” ligand. It i...
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hydrogen spillover on carbon supported metal catalysts studied by Inelastic Neutron Scattering surface vibrational states and hydrogen riding modes
Journal of Physical Chemistry B, 2003Co-Authors: Philip C H Mitchell, Stewart F. Parker, Anibal J Ramirezcuesta, J Tomkinson, David ThompsettAbstract: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 H2), and a weakly bound layer of mobile H atoms (formed by surface diffusion of H atoms after dissociative c...
S Rols - One of the best experts on this subject based on the ideXlab platform.
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the endofullerene hf c60 Inelastic Neutron Scattering spectra from quantum simulations and experiment validity of the selection rule and symmetry breaking
Journal of Physical Chemistry Letters, 2019Co-Authors: Peter M Felker, A J Horsewill, S Rols, Salvatore Mamone, Richard J Whitby, Zlatko BacicAbstract:Accurate quantum simulations of the low-temperature Inelastic Neutron Scattering (INS) spectra of HF@C60 are reported for two incident Neutron wavelengths. They are distinguished by the rigorous in...
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experimental theoretical and computational investigation of the Inelastic Neutron Scattering spectrum of a homonuclear diatomic molecule in a nearly spherical trap h2 c60
Physical Chemistry Chemical Physics, 2016Co-Authors: Salvatore Mamone, Mark R Johnson, S Rols, Monica Jimenezruiz, A J HorsewillAbstract:In this paper we report a methodology for calculating the Inelastic Neutron Scattering spectrum of homonuclear diatomic molecules confined within nano-cavities of spherical symmetry. The method is based on the expansion of the confining potential into multipoles of the coupled rotational and translational angular variables. The Hamiltonian and the INS transition probabilities are evaluated analytically. The method affords a fast and computationally inexpensive way to simulate the Inelastic Neutron Scattering spectrum of molecular hydrogen confined in fullerene cages. The potential energy surface is effectively parametrized in terms of few physical parameters comprising an harmonic term, anharmonic corrections and translation–rotation couplings. The parameters are refined by matching the simulations against the experiments and the excitation modes are identified for transfer energies up to 215 meV.
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confirming a predicted selection rule in Inelastic Neutron Scattering spectroscopy the quantum translator rotator h2 entrapped inside c60
Physical Review Letters, 2014Co-Authors: Monica Jimenezruiz, S Rols, Mark R Johnson, Marina Carravetta, Zlatko Bacic, Mark Denning, Xuegong Lei, A J HorsewillAbstract:We report an Inelastic Neutron Scattering (INS) study of H2 molecule encapsulated inside the fullerene C60 which confirms the recently predicted selection rule, the first to be established for the INS spectroscopy of aperiodic, discrete molecular compounds. Several transitions from the ground state of para-H2 to certain excited translation-rotation states, forbidden according to the selection rule, are systematically absent from the INS spectra, thus validating the selection rule with a high degree of confidence. Its confirmation sets a precedent, as it runs counter to the widely held view that the INS spectroscopy of molecular compounds is not subject to any selection rules.
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vibrational dynamics in dendridic oligoarylamines by raman spectroscopy and incoherent Inelastic Neutron Scattering
Journal of Physical Chemistry B, 2014Co-Authors: I Kulszewiczbajer, S Rols, G Louarn, David Djurado, Lukasz Skorka, Marek Zdzislaw Szymanski, Jean Yves Mevellec, Adam PronAbstract:Vibrational dynamics in triarylamine dendrimers was studied in a complementary way by Raman and infrared (IR) spectroscopies and incoherent Inelastic Neutron Scattering (IINS). Three molecules were investigated, namely, unsubstituted triarylamine dendrimer of the first generation and two dendrimers of the first and second generation, substituted in the crown with butyl groups. To facilitate the assignment of the observed IR and Raman modes as well as the IINS peaks, vibrational models, based on the general valence force field method (GVFF), were calculated for all three compounds studied. A perfect consistency between the calculated and experimental results was found. Moreover, an important complementarity of the vibrational spectroscopies and IINS was established for the investigated dendrimers. The IINS peaks originating mainly from the C–H motions were not restricted by particular selection rules and only dependent on the IINS cross section. To the contrary, Raman and IR bands were imposed by the selec...
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quantum rotation and translation of hydrogen molecules encapsulated inside c60 temperature dependence of Inelastic Neutron Scattering spectra
Philosophical Transactions of the Royal Society A, 2013Co-Authors: A J Horsewill, Yasujiro Murata, Kelvin S K Goh, S Rols, Jacques Ollivier, Mark R Johnson, Malcolm H Levitt, Marina Carravetta, Salvatore Mamone, Judy Y C ChenAbstract:The quantum dynamics of a hydrogen molecule encapsulated inside the cage of a C60 fullerene molecule is investigated using Inelastic Neutron Scattering (INS). The emphasis is on the temperature dep...
S. L. Chaplot - One of the best experts on this subject based on the ideXlab platform.
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anomalous lattice dynamics in agc4n3 insights from Inelastic Neutron Scattering and density functional calculations
Frontiers in Chemistry, 2018Co-Authors: Baltej Singh, S. L. Chaplot, R. Mittal, Mayanak K Gupta, Mohamed Zbiri, Sarah A Hodgson, Andrew L Goodwin, Helmut SchoberAbstract:We have performed temperature dependent Inelastic Neutron Scattering measurements to study the anharmonicity of phonon spectra of AgC4N3. The analysis and interpretation of the experimental spectra is done using ab-initio lattice dynamics calculations. The calculated phonon spectrum over the entire Brillion zone is used to derive linear thermal expansion coefficients. The effect of van der Waals interaction on structure stability has been investigated using advanced density functional methods. The calculated isothermal equation of states implies a negative linear compressibility along the c-axis of the crystal, which also leads to a negative thermal expansion along this direction. The role of elastic properties inducing the observed anomalous lattice behaviour is discussed.
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Inelastic Neutron Scattering and lattice dynamics perspectives and challenges in mineral physics
naee, 2009Co-Authors: Narayani Choudhury, S. L. ChaplotAbstract:An understanding of the fundamental physics of the Earth's interior requires information about the phase transitions and thermodynamic properties of key mantle-forming mineral phases. Inelastic Neutron Scattering (INS) is an indispensable tool for determining key lattice dynamics properties like the phonon dispersion relation (PDR) and density of states, which govern a wide range of material behaviors including structural phase transitions, thermodynamic properties, elasticity, and melting. In this chapter we review recent reported studies involving INS and lattice dynamics calculations of geophysically important minerals. We also review recent applications of INS involving experimental and theoretical ab initio and atomistic studies of the phonon spectra and thermodynamic properties of minerals and of other novel phenomena like high-pressure phonon softening, structural phase transitions, pressure-induced amorphization, magnetic excitations, melting, etc. We discuss the current understanding of the dynamical behavior, thermodynamic properties, and phase transitions of key mantle components like the olivine and pyroxene end members forsterite and enstatite, the mineral zircon, important silica polymorphs, and magnesium oxide; recent results on water and ice; other complex silicates; hydrogen storage materials; etc. Inelastic Neutron Scattering and complementary techniques like Inelastic X-ray Scattering have been used to explore the high-pressure PDR and density of states of iron, diamond, and magnesium oxide; to study magnetic excitations; to estimate the magnetic contributions to thermodynamic properties; etc. The theoretical calculations enable fruitful microscopic interpretations of complex experimental data and provide an atomic-level understanding of vibrational and thermodynamic properties.
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modeling of anomalous thermodynamic properties using lattice dynamics and Inelastic Neutron Scattering
Progress in Materials Science, 2006Co-Authors: R. Mittal, S. L. Chaplot, Niharendu ChoudhuryAbstract:Abstract This paper reviews some of the recent advances in the modeling of anomalous thermodynamic properties. Inelastic Neutron Scattering experiments in combination with lattice dynamics calculations are used to study the phonon properties as well as thermodynamic properties of several novel compounds. There is a large variation in the thermal expansion, specific heat and equation of state pertaining to the compounds described in this review. The interatomic potentials as determined for various compounds have been able to successfully model the thermodynamic behavior. Lattice dynamical calculations and high pressure Inelastic Neutron Scattering experiments indicate that large softening of several low energy phonons is mainly responsible for the negative thermal expansion in ZrW2O8, HfW2O8 and ZrMo2O8 up to 1443, 1050 and 600 K, respectively. It has been shown that a proper description of negative thermal expansion requires consideration of both the acoustic and optic phonon modes in the entire Brillouin zone. We have also reviewed studies on X-ray image storage materials MFX (M = Ba, Pb, Sr; X = Cl, Br, I); compounds MPO4 (M = Al, Fe and Ga); several garnet minerals M3Al2Si3O12 (M = Fe, Mg, Ca and Mn) and zircon (ZrSiO4). The variations in phonon spectra manifest in the thermodynamic properties of these compounds at high pressure and temperature. The calculations enable predictions and microscopic interpretation of the thermal expansion, specific heat and the equation of state.
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lattice dynamics and Inelastic Neutron Scattering experiments on andalusite al2sio5
Solid State Communications, 2002Co-Authors: Prabhatasree Goel, Narayani Choudhury, S. L. Chaplot, Subrata GhoseAbstract:Abstract We report coherent Inelastic Neutron Scattering measurements of the phonon dispersion relations and lattice dynamics shell model calculations of several microscopic and macroscopic properties of andalusite, Al 2 SiO 5 . Andalusite has an orthorhombic structure with 32 atoms/unit cell. The Inelastic Neutron Scattering measurements (up to energy transfers of 45 meV) were carried out using the triple axis spectrometer at Dhruva reactor, India using a single crystal of andalusite and the phonon dispersion relations along the [100] direction have been measured. The shell model calculations have been used to compute the crystal structure, elastic constants, phonon frequencies, dispersion relations, density of states and the specific heat. The calculated results are in good agreement with available experimental data. The computed one-phonon Neutron Scattering structure factors based on the shell model have been very useful in the planning and analysis of the Inelastic Neutron Scattering experiments.
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origin of negative thermal expansion in cubic zrw2o8 revealed by high pressure Inelastic Neutron Scattering
Physical Review Letters, 2001Co-Authors: R. Mittal, S. L. Chaplot, H Schober, T A MaryAbstract:Isotropic negative thermal expansion has been reported in cubic ZrW2O8 over a wide range of temperatures (0-1050 K). Here we report the direct experimental determination of the Gruneisen parameters of phonon modes as a function of their energy, averaged over the whole Brillouin zone, by means of high pressure Inelastic Neutron Scattering measurements. We observe a pronounced softening of the phonon spectrum at P = 1.7 kbar compared to that at ambient pressure by about 0.1-0.2 meV for phonons of energy below 8 meV. This unusual phonon softening on compression, corresponding to large negative Gruneisen parameters, is able to account for the observed large negative thermal expansion.
Anibal J Ramirezcuesta - One of the best experts on this subject based on the ideXlab platform.
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Inelastic Neutron Scattering evidence for anomalous h h distances in metal hydrides
Proceedings of the National Academy of Sciences of the United States of America, 2020Co-Authors: Andreas Borgschulte, Jasmin Terreni, Emanuel Billeter, Luke L Daemen, Yongqiang Cheng, Anup Pandey, Zbigniew łodziana, Russell J Hemley, Anibal J RamirezcuestaAbstract:Hydrogen-containing materials are of fundamental as well as technological interest. An outstanding question for both is the amount of hydrogen that can be incorporated in such materials, because that determines dramatically their physical properties such as electronic and crystalline structure. The number of hydrogen atoms in a metal is controlled by the interaction of hydrogens with the metal and by the hydrogen–hydrogen interactions. It is well established that the minimal possible hydrogen–hydrogen distances in conventional metal hydrides are around 2.1 A under ambient conditions, although closer H–H distances are possible for materials under high pressure. We present Inelastic Neutron Scattering measurements on hydrogen in Z r V 2 H x showing nonexpected Scattering at low-energy transfer. The analysis of the spectra reveals that these spectral features in part originate from hydrogen vibrations confined by neighboring hydrogen at distances as short as 1.6 A. These distances are much smaller than those found in related hydrides, thereby violating the so-called Switendick criterion. The results have implications for the design and creation of hydrides with additional properties and applications.
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simulation of Inelastic Neutron Scattering spectra using oclimax
Journal of Chemical Theory and Computation, 2019Co-Authors: Yongqiang Cheng, Luke L Daemen, A I Kolesnikov, Anibal J RamirezcuestaAbstract:Studying the vibration of atoms is of fundamental importance and can provide critical insight for the understanding of materials behavior, such as structure and phase transition, thermodynamics, and chemical reactions. The atomic vibration can be probed using vibrational spectroscopy with various incident particles such as photons, Neutrons, or electrons. A major challenge when applying these techniques is often how to interpret the vibrational spectra and how to make connections to the theory. To this end, methods that can simulate the spectra from atomistic models are highly desired. In this paper, we present a program developed for the simulation of Inelastic Neutron Scattering spectra. It has many new and useful features that were not previously available and will greatly facilitate the analysis and understanding of Inelastic Neutron Scattering data.
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identifying atomic scale structure in undoped doped semicrystalline p3ht using Inelastic Neutron Scattering
Macromolecules, 2017Co-Authors: Thomas F Harrelson, Yongqiang Cheng, Anibal J Ramirezcuesta, Ian E Jacobs, Roland Faller, Adam J MouleAbstract:The greatest advantage of organic materials is the ability to synthetically tune desired properties. However, structural heterogeneity often obfuscates the relationship between chemical structure and functional properties. Inelastic Neutron Scattering (INS) is sensitive to both local structure and chemical environment and provides atomic level details that cannot be obtained through other spectroscopic or diffraction methods. INS data are composed of a density of vibrational states with no selection rules, which means that every structural configuration is equally weighted in the spectrum. This allows the INS spectrum to be quantitatively decomposed into different structural motifs. We present INS measurements of the semiconducting polymer P3HT doped with F4TCNQ supported by density functional theory calculations to identify two dominant families of undoped crystalline structures and one dominant doped structural motif, in spite of considerable heterogeneity. The differences between the undoped and doped ...
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gate opening effect in zif 8 the first experimental proof using Inelastic Neutron Scattering
Chemical Communications, 2016Co-Authors: Mirian Elizabeth Casco, Luke L Daemen, Yongqiang Cheng, Anibal J Ramirezcuesta, David Fairenjimenez, Enrique V Ramosfernandez, Joaquin SilvestrealberoAbstract: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.
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Inelastic Neutron Scattering and raman spectroscopies and periodic dft studies of rb2pth6 and rb2ptd6
ChemInform, 2003Co-Authors: Stewart F. Parker, Anibal J Ramirezcuesta, Stephen M Bennington, Gudrun Auffermann, Welf Bronger, Henryk Herman, Kenneth P J Williams, Tim SmithAbstract:The present work has provided a complete set of assignments for the vibrational spectrum of Rb2PtH6 and Rb2PtD6. To confirm the assignments, a periodic density functional theory (DFT) code has been applied to the analysis of the Inelastic Neutron Scattering (INS) spectrum of an ionic material for the first time. The work has also provided an explanation for the unusual infrared spectrum of the potassium salt. The most significant aspect of the work is the use of the momentum transfer information provided by an INS chopper spectrometer. The straightforward method employed for the analysis of the data is applicable to any molecular system (organic or inorganic) and demonstrates the potential of these instruments for chemistry. Periodic DFT was also used to study the other A2PtH6 (A = alkali metal) including, the at present, unknown Li salt, which is found to be stable. The DFT studies have also highlighted the crucial role of the cation in removing charge from the transition metal and “hydride” ligand. It i...