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Zlatko Bacic - One of the best experts on this subject based on the ideXlab platform.
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intramolecular stretching vibrational states and frequency shifts of h2 2 confined inside the large cage of Clathrate Hydrate from an eight dimensional quantum treatment using small basis sets
Journal of Chemical Physics, 2019Co-Authors: Peter M Felker, Yohann Scribano, David Lauvergnat, David M Benoit, Zlatko BacicAbstract:We report the results of calculations pertaining to the HH intramolecular stretching fundamentals of (p-H2)2 encapsulated in the large cage of structure II Clathrate Hydrate. The eight-dimensional (8D) quantum treatment assumes rotationless (j = 0) H2 moieties and a rigid Clathrate structure but is otherwise fully coupled. The (H2)2-Clathrate interaction is constructed in a pairwise-additive fashion, by combining the ab initio H2–H2O pair potential for flexible H2 and rigid H2O [D. Lauvergnat et al., J. Chem. Phys. 150, 154303 (2019)] and the six-dimensional (6D) H2–H2 potential energy surface [R. J. Hinde, J. Chem. Phys. 128, 154308 (2008)]. The calculations are performed by first solving for the eigenstates of a reduced-dimension 6D “intermolecular” Hamiltonian extracted from the full 8D Hamiltonian by taking the H2 moieties to be rigid. An 8D contracted product basis for the solution of the full problem is then constructed from a small number of the lowest-energy 6D intermolecular eigenstates and two discrete variable representations covering the H2-monomer internuclear distances. Converged results are obtained already by including just the two lowest intermolecular eigenstates in the final 8D basis of dimension 128. The two HH vibrational stretching fundamentals are computed for three Hydrate domains having an increasing number of H2O molecules. For the largest domain, the two fundamentals are found to be site-split by ∼0.5 cm−1 and to be redshifted by about 24 cm−1 from the free-H2 monomer stretch frequency, in excellent agreement with the experimental value of 26 cm−1. A first-order perturbation theory treatment gives results that are nearly identical to those of the 8D quantum calculations.We report the results of calculations pertaining to the HH intramolecular stretching fundamentals of (p-H2)2 encapsulated in the large cage of structure II Clathrate Hydrate. The eight-dimensional (8D) quantum treatment assumes rotationless (j = 0) H2 moieties and a rigid Clathrate structure but is otherwise fully coupled. The (H2)2-Clathrate interaction is constructed in a pairwise-additive fashion, by combining the ab initio H2–H2O pair potential for flexible H2 and rigid H2O [D. Lauvergnat et al., J. Chem. Phys. 150, 154303 (2019)] and the six-dimensional (6D) H2–H2 potential energy surface [R. J. Hinde, J. Chem. Phys. 128, 154308 (2008)]. The calculations are performed by first solving for the eigenstates of a reduced-dimension 6D “intermolecular” Hamiltonian extracted from the full 8D Hamiltonian by taking the H2 moieties to be rigid. An 8D contracted product basis for the solution of the full problem is then constructed from a small number of the lowest-energy 6D intermolecular eigenstates and two d...
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intramolecular stretching vibrational states and frequency shifts of h2 2 confined inside the large cage of Clathrate Hydrate from an eight dimensional quantum treatment using small basis sets
Journal of Chemical Physics, 2019Co-Authors: Peter M Felker, Yohann Scribano, David Lauvergnat, David M Benoit, Zlatko BacicAbstract:We report the results of calculations pertaining to the HH intramolecular stretching fundamentals of (p-H2)2 encapsulated in the large cage of structure II Clathrate Hydrate. The eight-dimensional (8D) quantum treatment assumes rotationless (j = 0) H2 moieties and a rigid Clathrate structure but is otherwise fully coupled. The (H2)2-Clathrate interaction is constructed in a pairwise-additive fashion, by combining the ab initio H2-H2O pair potential for flexible H2 and rigid H2O [D. Lauvergnat et al., J. Chem. Phys. 150, 154303 (2019)] and the six-dimensional (6D) H2-H2 potential energy surface [R. J. Hinde, J. Chem. Phys. 128, 154308 (2008)]. The calculations are performed by first solving for the eigenstates of a reduced-dimension 6D "intermolecular" Hamiltonian extracted from the full 8D Hamiltonian by taking the H2 moieties to be rigid. An 8D contracted product basis for the solution of the full problem is then constructed from a small number of the lowest-energy 6D intermolecular eigenstates and two discrete variable representations covering the H2-monomer internuclear distances. Converged results are obtained already by including just the two lowest intermolecular eigenstates in the final 8D basis of dimension 128. The two HH vibrational stretching fundamentals are computed for three Hydrate domains having an increasing number of H2O molecules. For the largest domain, the two fundamentals are found to be site-split by ∼0.5 cm-1 and to be redshifted by about 24 cm-1 from the free-H2 monomer stretch frequency, in excellent agreement with the experimental value of 26 cm-1. A first-order perturbation theory treatment gives results that are nearly identical to those of the 8D quantum calculations.
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h2 hd and d2 in the small cage of structure ii Clathrate Hydrate vibrational frequency shifts from fully coupled quantum six dimensional calculations of the vibration translation rotation eigenstates
Journal of Chemical Physics, 2019Co-Authors: David Lauvergnat, Yohann Scribano, David M Benoit, Zlatko Bacic, Peter FelkerAbstract:We report the first fully coupled quantum six-dimensional (6D) bound-state calculations of the vibration-translation-rotation eigenstates of a flexible H2, HD, and D2 molecule confined inside the small cage of the structure II Clathrate Hydrate embedded in larger Hydrate domains with up to 76 H2O molecules, treated as rigid. Our calculations use a pairwise-additive 6D intermolecular potential energy surface for H2 in the Hydrate domain, based on an ab initio 6D H2–H2O pair potential for flexible H2 and rigid H2O. They extend to the first excited (v = 1) vibrational state of H2, along with two isotopologues, providing a direct computation of vibrational frequency shifts. We show that obtaining a converged v = 1 vibrational state of the caged molecule does not require converging the very large number of intermolecular translation-rotation states belonging to the v = 0 manifold up to the energy of the intramolecular stretch fundamental (≈4100 cm−1 for H2). Only a relatively modest-size basis for the intermolecular degrees of freedom is needed to accurately describe the vibrational averaging over the delocalized wave function of the quantum ground state of the system. For the caged H2, our computed fundamental translational excitations, rotational j = 0 → 1 transitions, and frequency shifts of the stretch fundamental are in excellent agreement with recent quantum 5D (rigid H2) results [A. Powers et al., J. Chem. Phys. 148, 144304 (2018)]. Our computed frequency shift of −43 cm−1 for H2 is only 14% away from the experimental value at 20 K.We report the first fully coupled quantum six-dimensional (6D) bound-state calculations of the vibration-translation-rotation eigenstates of a flexible H2, HD, and D2 molecule confined inside the small cage of the structure II Clathrate Hydrate embedded in larger Hydrate domains with up to 76 H2O molecules, treated as rigid. Our calculations use a pairwise-additive 6D intermolecular potential energy surface for H2 in the Hydrate domain, based on an ab initio 6D H2–H2O pair potential for flexible H2 and rigid H2O. They extend to the first excited (v = 1) vibrational state of H2, along with two isotopologues, providing a direct computation of vibrational frequency shifts. We show that obtaining a converged v = 1 vibrational state of the caged molecule does not require converging the very large number of intermolecular translation-rotation states belonging to the v = 0 manifold up to the energy of the intramolecular stretch fundamental (≈4100 cm−1 for H2). Only a relatively modest-size basis for the intermol...
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h 2 hd and d 2 in the small cage of structure ii Clathrate Hydrate vibrational frequency shifts from fully coupled quantum six dimensional calculations of the vibration translation rotation eigenstates
Journal of Chemical Physics, 2019Co-Authors: David Lauvergnat, Yohann Scribano, David M Benoit, Peter M Felker, Zlatko BacicAbstract:We report the first fully coupled quantum six-dimensional (6D) bound-state calculations of the vibration-translation-rotation eigenstates of a flexible H2, HD, and D2 molecule confined inside the small cage of the structure II Clathrate Hydrate embedded in larger Hydrate domains with up to 76 H2O molecules, treated as rigid. Our calculations use a pairwise-additive 6D intermolecular potential energy surface for H2 in the Hydrate domain, based on an ab initio 6D H2–H2O pair potential for flexible H2 and rigid H2O. They extend to the first excited (v = 1) vibrational state of H2, along with two isotopologues, providing a direct computation of vibrational frequency shifts. We show that obtaining a converged v = 1 vibrational state of the caged molecule does not require converging the very large number of intermolecular translation-rotation states belonging to the v = 0 manifold up to the energy of the intramolecular stretch fundamental (≈4100 cm−1 for H2). Only a relatively modest-size basis for the intermolecular degrees of freedom is needed to accurately describe the vibrational averaging over the delocalized wave function of the quantum ground state of the system. For the caged H2, our computed fundamental translational excitations, rotational j = 0 → 1 transitions, and frequency shifts of the stretch fundamental are in excellent agreement with recent quantum 5D (rigid H2) results [A. Powers et al., J. Chem. Phys. 148, 144304 (2018)]. Our computed frequency shift of −43 cm−1 for H2 is only 14% away from the experimental value at 20 K.We report the first fully coupled quantum six-dimensional (6D) bound-state calculations of the vibration-translation-rotation eigenstates of a flexible H2, HD, and D2 molecule confined inside the small cage of the structure II Clathrate Hydrate embedded in larger Hydrate domains with up to 76 H2O molecules, treated as rigid. Our calculations use a pairwise-additive 6D intermolecular potential energy surface for H2 in the Hydrate domain, based on an ab initio 6D H2–H2O pair potential for flexible H2 and rigid H2O. They extend to the first excited (v = 1) vibrational state of H2, along with two isotopologues, providing a direct computation of vibrational frequency shifts. We show that obtaining a converged v = 1 vibrational state of the caged molecule does not require converging the very large number of intermolecular translation-rotation states belonging to the v = 0 manifold up to the energy of the intramolecular stretch fundamental (≈4100 cm−1 for H2). Only a relatively modest-size basis for the intermol...
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rigorous quantum treatment of inelastic neutron scattering spectra of a heteronuclear diatomic molecule in a nanocavity hd in the small cage of structure ii Clathrate Hydrate
Chemical Physics Letters, 2013Co-Authors: Lorenzo Ulivi, Zlatko Bacic, Milva Celli, D ColognesiAbstract:Abstract We present a novel methodology which allows rigorous quantum calculation of the inelastic neutron scattering (INS) spectra of a heteronuclear diatomic molecule confined inside a nanoscale cavity of an arbitrary shape. This generalizes the approach recently developed by us for the quantum simulation of the INS spectra of nanoconfined homonuclear diatomics. The key distinguishing feature of our approach is the use of the fully coupled 5D translation–rotation (TR) energy levels and wave functions as the initial and final states of the INS transitions. The computed INS spectra embody the full complexity of the quantum TR dynamics of the guest heteronuclear molecule in the anisotropic confinement and are therefore highly realistic. Utilizing this methodology, we compute at several temperatures the INS spectra of HD molecule in the small cage of the structure II Clathrate Hydrate, which are in very good overall agreement with the experimental INS spectra.
Ryo Ohmura - One of the best experts on this subject based on the ideXlab platform.
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crystal growth of Clathrate Hydrate with methane plus partially water soluble large molecule guest compound
Crystal Growth & Design, 2019Co-Authors: Kazuya Ozawa, Ryo OhmuraAbstract:This paper reports the visual observations of the formation and growth of Clathrate Hydrate formed with methane plus a partially water soluble guest, tetrahydropyran (THP). THP is known to form a s...
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selective occupancy of methane by cage symmetry in tbab ionic Clathrate Hydrate
Chemical Communications, 2016Co-Authors: Sanehiro Muromachi, Saman Alavi, Ryo Ohmura, Konstantin A Udachin, John A RipmeesterAbstract:Methane trapped in the two distinct dodecahedral cages of the ionic Clathrate Hydrate of TBAB was studied by single crystal XRD and MD simulation. The relative CH4 occupancies over the cage types were opposite to those of CO2, which illustrates the interplay between the cage symmetry and guest shape and dynamics, and thus the gas selectivity.
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phase behavior and structural characterization of ionic Clathrate Hydrate formed with tetra n butylphosphonium hydroxide discovery of primitive crystal structure
Crystal Growth & Design, 2015Co-Authors: Takayuki Kobori, Saman Alavi, Satoshi Takeya, Sanehiro Muromachi, Tatsuro Yamasaki, Yoshitaka Yamamoto, Ryo OhmuraAbstract:This paper reports phase equilibrium measurements and crystal structure analysis on the ionic Clathrate Hydrate formed from tetra-n-butylphosphonium hydroxide (TBPOH). Phase equilibrium temperatures were measured in the mole fraction range of TBPOH in aqueous solution from 0.0072 to 0.0416. The highest ionic Clathrate Hydrate–solution equilibrium temperature was determined to be 290.2 K at a TBPOH mole fraction of 0.0340, which corresponds to the congruent composition. Single-crystal X-ray diffraction measurements were performed on the crystal formed at 288.7 K, and the chemical composition of the TBPOH Hydrate crystal was determined to be TBPOH·29.6H2O, which is consistent with the congruent composition obtained by the phase equilibrium measurement. The crystal structure of the TBPOH Hydrate has a superstructure identical with Jeffrey’s type I cubic structure, with an I43d space group with a lattice constant of 24.5191(13) A. The TBPOH Hydrate structure is compared with the same Hydrate structure formed...
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surfactant effects on the crystal growth of Clathrate Hydrate at the interface of water and hydrophobic guest liquid
Crystal Growth & Design, 2015Co-Authors: Makoto Mitarai, Masatoshi Kishimoto, Donguk Suh, Ryo OhmuraAbstract:Visual observations of the effect of surfactants on Clathrate Hydrate crystal growth at the interface of water and cyclopentane has been studied. Surfactants used in the present study are sorbitan monooleate (Span 80), naphthenic acid, and polypropylene glycol. The surfactants were each used at a mass fraction of 0.001% and 0.01%. All the surfactants were soluble in cyclopentane. The crystalline morphology and crystal growth behavior of the Hydrate at the interface were found to be substantially affected by the addition of all surfactants. The size of the individual Hydrate crystals in the surfactant system was larger than those in the pure cyclopentane system. The observations showed a distinct variation in the behavior of cyclopentane Hydrate crystal growth depending on the chemical species of the surfactants, their concentration, and ΔTsub, which is defined as the difference between the equilibrium temperature and the experimental temperature. For the system with surfactants, the growing Hydrate crysta...
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Phase Behavior and Structural Characterization of Ionic Clathrate Hydrate Formed with Tetra‑n‑butylphosphonium Hydroxide: Discovery of Primitive Crystal Structure
2015Co-Authors: Takayuki Kobori, Saman Alavi, Satoshi Takeya, Sanehiro Muromachi, Tatsuro Yamasaki, Yoshitaka Yamamoto, Ryo OhmuraAbstract:This paper reports phase equilibrium measurements and crystal structure analysis on the ionic Clathrate Hydrate formed from tetra-n-butylphosphonium hydroxide (TBPOH). Phase equilibrium temperatures were measured in the mole fraction range of TBPOH in aqueous solution from 0.0072 to 0.0416. The highest ionic Clathrate Hydrate–solution equilibrium temperature was determined to be 290.2 K at a TBPOH mole fraction of 0.0340, which corresponds to the congruent composition. Single-crystal X-ray diffraction measurements were performed on the crystal formed at 288.7 K, and the chemical composition of the TBPOH Hydrate crystal was determined to be TBPOH·29.6H2O, which is consistent with the congruent composition obtained by the phase equilibrium measurement. The crystal structure of the TBPOH Hydrate has a superstructure identical with Jeffrey’s type I cubic structure, with an I4̅3d space group with a lattice constant of 24.5191(13) Å. The TBPOH Hydrate structure is compared with the same Hydrate structure formed by the tetra-n-butylammonium fluoride. We provide a comprehensive overview of the dissociation temperature, the counteranion, and the Hydrate structure regarding TBP and TBA salt Hydrates. The dissociation temperatures decrease linearly with the increase in the partial molal volume of anions for TBA and TBP salt Hydrates, changing the Hydrate structures from the primitive cubic one that has the minimum hydration number
John A Ripmeester - One of the best experts on this subject based on the ideXlab platform.
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comment on quasi elastic neutron scattering investigation of the guest molecule dynamics in the bromomethane Clathrate Hydrate
Fluid Phase Equilibria, 2017Co-Authors: John A Ripmeester, Christopher I RatcliffeAbstract:Abstract This comment addresses several points presented in a recent paper in the Journal that affect the interpretation of data obtained in a study of quasi-elastic neutron scattering in methyl bromide Clathrate Hydrate. The Clathrate belongs to a class known as cubic structure I and it has two sites in its hydrogen-bonded network suitable for guest molecules, one in the large cavity in the structure, the other in the small cavity. The data obtained for methyl bromide Hydrate were assigned to the two presumed populations of methyl bromide molecules. However, previous composition measurements and NMR data have shown that the small cavity in fact does not contain methyl bromide molecules. This also becomes obvious once the dimensions of the methyl bromide and the host cavity are calculated, the molecule being too large to fit into the cavity by nearly 0.1 nm. Thus the interpretation of data as assigned in the paper cannot be correct. Finally, although the authors claim new insights into guest –host interactions from guest dynamics, this should be presented in light of previous relevant work where this topic has been thoroughly evaluated.
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some current challenges in Clathrate Hydrate science nucleation decomposition and the memory effect
Current Opinion in Solid State & Materials Science, 2016Co-Authors: John A Ripmeester, Saman AlaviAbstract:Abstract Among outstanding issues still to be understood regarding the Clathrate Hydrates are the mechanism of the processes involved in the formation and decomposition of Clathrates: nucleation, decomposition, and the memory effect during reformation. The latter involves the shorter induction times required for solutions of decomposed Hydrate to nucleate as compared to those for freshly prepared solutions. The formation of the Clathrate Hydrate phases of insoluble gases in water is accompanied by a ∼6000 fold concentration of the gas content in the solid phase compared to the aqueous phase from which it forms. The nucleation mechanism for the solid Hydrate which allows the delivery of such high concentration of gas and water in one location has been the subject of much experimental and computational study. While these studies have improved our understanding of the nucleation process, many unknown aspects remain. These developments are described in this Opinion.
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selective occupancy of methane by cage symmetry in tbab ionic Clathrate Hydrate
Chemical Communications, 2016Co-Authors: Sanehiro Muromachi, Saman Alavi, Ryo Ohmura, Konstantin A Udachin, John A RipmeesterAbstract:Methane trapped in the two distinct dodecahedral cages of the ionic Clathrate Hydrate of TBAB was studied by single crystal XRD and MD simulation. The relative CH4 occupancies over the cage types were opposite to those of CO2, which illustrates the interplay between the cage symmetry and guest shape and dynamics, and thus the gas selectivity.
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effect of small cage guests on hydrogen bonding of tetrahydrofuran in binary structure ii Clathrate Hydrates
Journal of Chemical Physics, 2012Co-Authors: Saman Alavi, John A RipmeesterAbstract:Molecular dynamics simulations of the pure structure II tetrahydrofuran Clathrate Hydrate and binary structure II tetrahydrofuran Clathrate Hydrate with CO2, CH4, H2S, and Xe small cage guests are performed to study the effect of the shape, size, and intermolecular forces of the small cages guests on the structure and dynamics of the Hydrate. The simulations show that the number and nature of the guest in the small cage affects the probability of hydrogen bonding of the tetrahydrofuran guest with the large cage water molecules. The effect on hydrogen bonding of tetrahydrofuran occurs despite the fact that the guests in the small cage do not themselves form hydrogen bonds with water. These results indicate that nearest neighbour guest-guest interactions (mediated through the water lattice framework) can affect the Clathrate structure and stability. The implications of these subtle small guest effects on Clathrate Hydrate stability are discussed.
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molecular dynamics and first principles calculations of raman spectra and molecular and electronic structure of hydrogen clusters in hydrogen Clathrate Hydrate
Journal of Physical Chemistry C, 2010Co-Authors: Jianwei Wang, John A Ripmeester, Udo BeckerAbstract:Molecular-dynamics simulations and first-principles calculations are employed to understand vibrational spectroscopy and molecular and electronic structure of the encaged hydrogen molecules in hydrogen Clathrate Hydrate. The molecular-dynamics simulations, using empirical potentials, are performed to generate collections of the Clathrate water cages with different hydrogen occupancies. The first-principles calculations, using Density Functional Theory with B3LYP hybrid density functionals for exchange and correlation, are carried out to optimize the structures and to calculate the Raman shift and activity of the stretching mode of the encaged hydrogen molecules. The Raman spectra are computed by a weighted moving average over a number of different structural configurations for different hydrogen occupancies. The results show that experimentally observed Raman peaks around 4120-4125 cm -1 are from small cages with single H2 occupancy and peaks around 4125-4150 cm -1 from those in the large cages with one to four H2 molecules. The Raman peaks of hydrogen molecules in the doubly occupied small cages are expected to be around or above the gas phase frequency 4155 cm -1 . Molecular structural analysis shows that the single hydrogen molecule in the small cages and single to quadruple hydrogen molecules in the large cage are encaged in loose cages, while double hydrogen molecules in the small cage are confined in a tight cage. Normal-mode analysis shows that there is limited vibrational coupling for H2 molecules in doubly to quadruply occupied large cages while a strong vibrational coupling is observed in the doubly occupied small cage. The isovalue maps of total electron density and electrostatic potential suggest significant electron sharing between hydrogen molecules and water molecules, and important interaction between hydrogen and water oxygen atoms for confining the hydrogen clusters. The results help explain experimentally observed Raman spectra of hydrogen Clathrates and provide new insights into the confinement effect by the water host framework on vibrational, molecular, and electronic properties of hydrogen molecules in the cages of Clathrate Hydrates.
Dendy E Sloan - One of the best experts on this subject based on the ideXlab platform.
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adhesion force between cyclopentane Hydrate and mineral surfaces
Langmuir, 2013Co-Authors: Zachary M Aman, William J Leith, Giovanny Grasso, Dendy E SloanAbstract:Clathrate Hydrate adhesion forces play a critical role in describing aggregation and deposition behavior in conventional energy production and transportation. This manuscript uses a unique micromechanical force apparatus to measure the adhesion force between cyclopentane Hydrate and heterogeneous quartz and calcite substrates. The latter substrates represent models for coproduced sand and scale often present during conventional energy production and transportation. Micromechanical adhesion force data indicate that Clathrate Hydrate adhesive forces are 5–10× larger for calcite and quartz minerals than stainless steel. Adhesive forces further increased by 3–15× when increasing surface contact time from 10 to 30 s. In some cases, liquid water from within the Hydrate shell contacted the mineral surface and rapidly converted to Clathrate Hydrate. Further measurements on mineral surfaces with physical control of surface roughness showed a nonlinear dependence of water wetting angle on surface roughness. Existin...
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interfacial mechanisms governing cyclopentane Clathrate Hydrate adhesion cohesion
Physical Chemistry Chemical Physics, 2011Co-Authors: Zachary Mark Aman, Erika P Brown, Dendy E SloanAbstract:The present work uses a micromechanical force apparatus to directly measure cyclopentane Clathrate Hydrate cohesive force and Hydrate-steel adhesive force, as a function of contact time, contact force and temperature. We present a Hydrate interparticle force model, which includes capillary and sintering contributions and is based on fundamental interparticle force theories. In this process, we estimate the cyclopentane Hydrate tensile strength to be approximately 0.91 MPa. This Hydrate interparticle force model also predicts the effect of temperature on Hydrate particle cohesion force. Finally, we present the first direct measurements of Hydrate cohesive force in the gas phase to be 9.1 ± 2.1 mN/m at approximately 3 °C (as opposed to 4.3 ± 0.4 mN/m in liquid cyclopentane).
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water cavities of sh Clathrate Hydrate stabilized by molecular hydrogen
Journal of Physical Chemistry B, 2008Co-Authors: Timothy A Strobel, Carolyn A Koh, Dendy E SloanAbstract:X-ray diffraction and Raman spectroscopic measurements confirm that molecular hydrogen can be contained within the small water cavities of a binary sH Clathrate Hydrate using large guest molecules that stabilize the large cavity. The potential increase in hydrogen storage could be more than 40% when compared with binary sII Hydrates. This work demonstrates the stabilization of hydrogen in a Hydrate structure previously unknown for encapsulating molecular hydrogen, indicating the potential for other inclusion compound materials with even greater hydrogen storage capabilities.
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a hydrogen Clathrate Hydrate with cyclohexanone structure and stability
Journal of the American Chemical Society, 2007Co-Authors: Timothy A Strobel, Dendy E Sloan, Keith C Hester, Carolyn A KohAbstract:High-resolution neutron diffraction measurements have been used to confirm the crystal structure of the binary Clathrate Hydrate of cyclohexanone and hydrogen, making cyclohexanone one of the largest known sII Hydrate formers. The position, orientation, and occupancy of the guest molecules within the Hydrate cavities have been determined. Because cyclohexanone falls into the class of large sII forming molecules that require a second guest for stability, the role of hydrogen in Hydrate stability is further elucidated. From these results, we suggest that the stabilization behavior of hydrogen is analogous to that of other more common Hydrate forming molecules and suggest that hydrogen has the potential to stabilize other Clathrate structures with greater hydrogen storage capacity.
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stable low pressure hydrogen clusters stored in a binary Clathrate Hydrate
Science, 2004Co-Authors: L J Florusse, C J Peters, Joop Schoonman, Keith C Hester, Kenneth N Marsh, Dendy E SloanAbstract:Thermodynamic, x-ray diffraction, and Raman and nuclear magnetic resonance spectroscopy measurements show that clusters of H2 can be stabilized and stored at low pressures in a sII binary Clathrate Hydrate. Clusters of H2 molecules occupy small water cages, whereas large water cages are singly occupied by tetrahydrofuran. The presence of this second guest component stabilizes the Clathrate at pressures of 5 megapascals at 279.6 kelvin, versus 300 megapascals at 280 kelvin for pure H2 Hydrate.
Saman Alavi - One of the best experts on this subject based on the ideXlab platform.
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some current challenges in Clathrate Hydrate science nucleation decomposition and the memory effect
Current Opinion in Solid State & Materials Science, 2016Co-Authors: John A Ripmeester, Saman AlaviAbstract:Abstract Among outstanding issues still to be understood regarding the Clathrate Hydrates are the mechanism of the processes involved in the formation and decomposition of Clathrates: nucleation, decomposition, and the memory effect during reformation. The latter involves the shorter induction times required for solutions of decomposed Hydrate to nucleate as compared to those for freshly prepared solutions. The formation of the Clathrate Hydrate phases of insoluble gases in water is accompanied by a ∼6000 fold concentration of the gas content in the solid phase compared to the aqueous phase from which it forms. The nucleation mechanism for the solid Hydrate which allows the delivery of such high concentration of gas and water in one location has been the subject of much experimental and computational study. While these studies have improved our understanding of the nucleation process, many unknown aspects remain. These developments are described in this Opinion.
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selective occupancy of methane by cage symmetry in tbab ionic Clathrate Hydrate
Chemical Communications, 2016Co-Authors: Sanehiro Muromachi, Saman Alavi, Ryo Ohmura, Konstantin A Udachin, John A RipmeesterAbstract:Methane trapped in the two distinct dodecahedral cages of the ionic Clathrate Hydrate of TBAB was studied by single crystal XRD and MD simulation. The relative CH4 occupancies over the cage types were opposite to those of CO2, which illustrates the interplay between the cage symmetry and guest shape and dynamics, and thus the gas selectivity.
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phase behavior and structural characterization of ionic Clathrate Hydrate formed with tetra n butylphosphonium hydroxide discovery of primitive crystal structure
Crystal Growth & Design, 2015Co-Authors: Takayuki Kobori, Saman Alavi, Satoshi Takeya, Sanehiro Muromachi, Tatsuro Yamasaki, Yoshitaka Yamamoto, Ryo OhmuraAbstract:This paper reports phase equilibrium measurements and crystal structure analysis on the ionic Clathrate Hydrate formed from tetra-n-butylphosphonium hydroxide (TBPOH). Phase equilibrium temperatures were measured in the mole fraction range of TBPOH in aqueous solution from 0.0072 to 0.0416. The highest ionic Clathrate Hydrate–solution equilibrium temperature was determined to be 290.2 K at a TBPOH mole fraction of 0.0340, which corresponds to the congruent composition. Single-crystal X-ray diffraction measurements were performed on the crystal formed at 288.7 K, and the chemical composition of the TBPOH Hydrate crystal was determined to be TBPOH·29.6H2O, which is consistent with the congruent composition obtained by the phase equilibrium measurement. The crystal structure of the TBPOH Hydrate has a superstructure identical with Jeffrey’s type I cubic structure, with an I43d space group with a lattice constant of 24.5191(13) A. The TBPOH Hydrate structure is compared with the same Hydrate structure formed...
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Phase Behavior and Structural Characterization of Ionic Clathrate Hydrate Formed with Tetra‑n‑butylphosphonium Hydroxide: Discovery of Primitive Crystal Structure
2015Co-Authors: Takayuki Kobori, Saman Alavi, Satoshi Takeya, Sanehiro Muromachi, Tatsuro Yamasaki, Yoshitaka Yamamoto, Ryo OhmuraAbstract:This paper reports phase equilibrium measurements and crystal structure analysis on the ionic Clathrate Hydrate formed from tetra-n-butylphosphonium hydroxide (TBPOH). Phase equilibrium temperatures were measured in the mole fraction range of TBPOH in aqueous solution from 0.0072 to 0.0416. The highest ionic Clathrate Hydrate–solution equilibrium temperature was determined to be 290.2 K at a TBPOH mole fraction of 0.0340, which corresponds to the congruent composition. Single-crystal X-ray diffraction measurements were performed on the crystal formed at 288.7 K, and the chemical composition of the TBPOH Hydrate crystal was determined to be TBPOH·29.6H2O, which is consistent with the congruent composition obtained by the phase equilibrium measurement. The crystal structure of the TBPOH Hydrate has a superstructure identical with Jeffrey’s type I cubic structure, with an I4̅3d space group with a lattice constant of 24.5191(13) Å. The TBPOH Hydrate structure is compared with the same Hydrate structure formed by the tetra-n-butylammonium fluoride. We provide a comprehensive overview of the dissociation temperature, the counteranion, and the Hydrate structure regarding TBP and TBA salt Hydrates. The dissociation temperatures decrease linearly with the increase in the partial molal volume of anions for TBA and TBP salt Hydrates, changing the Hydrate structures from the primitive cubic one that has the minimum hydration number
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water proton configurations in structures i ii and h Clathrate Hydrate unit cells
Journal of Chemical Physics, 2013Co-Authors: Fumihito Takeuchi, Saman Alavi, Ryo Ohmura, Masaki Hiratsuka, Amadeu K Sum, Kenji YasuokaAbstract:Position and orientation of water protons need to be specified when the molecular simulation studies are performed for Clathrate Hydrates. Positions of oxygen atoms in water are experimentally determined by X-ray diffraction analysis of Clathrate Hydrate structures, but positions of water hydrogen atoms in the lattice are disordered. This study reports a determination of the water proton coordinates in unit cell of structure I (sI), II (sII), and H (sH) Clathrate Hydrates that satisfy the ice rules, have the lowest potential energy configuration for the protons, and give a net zero dipole moment. Possible proton coordinates in the unit cell were chosen by analyzing the symmetry of protons on the hexagonal or pentagonal faces in the Hydrate cages and generating all possible proton distributions which satisfy the ice rules. We found that in the sI and sII unit cells, proton distributions with small net dipole moments have fairly narrow potential energy spreads of about 1 kJ/mol. The total Coulomb potential on a test unit charge placed in the cage center for the minimum energy/minimum dipole unit cell configurations was calculated. In the sI small cages, the Coulomb potential energy spread in each class of cage is less than 0.1 kJ/mol, while the potential energy spread increases to values up to 6 kJ/mol in sH and 15 kJ/mol in the sII cages. The guest environments inside the cages can therefore be substantially different in the sII case. Cartesian coordinates for oxygen and hydrogen atoms in the sI, sII, and sH unit cells are reported for reference.