Crossover between the thermodynamic and nonequilibrium scenarios of structural transformations of H<Subscript>2</Subscript>O I<Emphasis Type="Italic">h</Emphasis> ice during compression

A detailed investigation of different scenarios of structural transformations of H₂O Ih ice during compression to a pressure of 2 GPa in the temperature range from 77 to 200 K is performed. In the range of temperatures and pressures being treated, detailed data are obtained for the density and the shear modulus for different phases of ice including the hda, IX, and XII phases. The experimentally obtained correlations for the density and ultrasonic velocities, with due regard for the available data of structural investigations, are used to identify the transformation sequences Ih→hda (below 135 K), Ih→II→VI (above 165 K), and Ih→IX→VI (from 155 to 180 K). In the vicinity of the crystallization temperature of amorphous ice, i.e., at about 140 K, an anomalous transformation pattern is observed, which is interpreted as predominantly the Ih→XII phase transition. The temperature crossover is discussed between the mode of solid-phase amorphization (Ih→hda) and crystal-crystal transitions, as well as the metastable nature of IX ice and the mechanism of solid-phase amorphization.     

Influence of water on HFO-1234yf oxidation pyrolysis via ReaxFF molecular dynamics simulation

ABSTRACT

The effect of water molecules on HFO-1234yf oxidation pyrolysis was investigated by ReaxFF-molecular dynamics simulation from 1900 to 4200?K. The initial pyrolysis of HFO-1234yf starts around 2500?K and the water molecules participate in chemical reactions at 2800?K when the reactants pyrolysis reached the highest reaction rate. The primary products including HF, COF₂ and CO₂ are observed at 2600, 2700 and 2900?K, respectively. The influence of water molecules on products is mainly reflected in the promotion activity on the conversion from COF₂ to CO₂ and the generation of HF molecules. Four formation pathways are observed and calculated to further elucidate the procedure of pyrolysis. The main conversion process from H₂O to HF is the ?F?+?H₂O?=?HF+?OH reaction, and the paths from H₂O to ?OH radical and COF₂ to ?CFO radical which are promoted by ?F and ?H radical, respectively, have relatively low energy barriers of 10.44 and 40.29?kJ/mol, and both reaction processes released HF molecules.     

Ejection of H2O,O2, H2 and H from water ice by 0.5–6 keV H+ and Ne+ ion bombardment

The ejection of H₂O, O₂, H₂ and H from water ice at 30–140 K, bombarded by 0.5–6 keV H⁺ and Ne⁺ was studied experimentally. Neon ions in this energy range deposit their energy in the ice by nuclear collisions, whereas with protons of 0.5 to 6 keV the energy deposition mechanism shifts gradually from predominantly nuclear collisions to predominantly electronic processes. The existing theory of nuclear sputtering predicts very well the yield of ejected water molecules and the experimental results in the region of electronic processes agree well with the experimental results of Lanzerotti, Brown and Johnson. However, the major mass loss from water by ion bombardment is via the ejection of O₂, H₂ and H atoms, which exceed the ejection of water molecules. O₂ and H₂ production is markedly enhanced at temperatures exceeding ~100 K, whereas H₂O and H production are temperature independent, suggesting that O₂ and H₂ are produced in the bulk of the ice whereas H₂O and H atoms are ejected from the surface or near surface layers.     

NEUTRON SCATTERING AND LATTICE DYNAMICAL STUDIES OF THE HIGH-PRESSURE PHASE ICE (II)

Lattice dynamical calculations have been carried out for ice II based on the force field constructed for ice Ih. In order to fully understand ice II inelastic neutron scattering spectra, the decomposed phonon density of states was shown mode by mode. Calculated results have shown that the hydrogen bond force constant between the six-molecule rings is significantly weaker, 75eV/nm², compared with the force constant, 220eV/nm², within the rings. Inelastic neutron scattering spectra of clathrate hydrate H₂O+He are almost the same as ice II. This means that the absorption of He atoms cannot affect the bond strengths of the ice II host lattice. Based on the force field model for ice II, the van der Waals interactions between water molecules and helium atoms are considered. The results obtained are consistent with experimental data. Lattice dynamical calculations have been carried out for ice II using seven rigid pairwise potentials. It was found that MCY makes the stretching and bending interactions in ice II too weak and makes the O-O bond length too long (～5%), thus its lattice densities are obviously lower than other potential lattices or experimental values.     

The growth of ice clusters on the Si(100)(2 × 1)-H(D) surface: Electron energy loss spectroscopy and thermal desorption studies

The growth of ice clusters on the Si(100)(2 × 1)-H surface has been investigated mainly by the use of high-resolution electron energy loss spectroscopy and thermal desorption spectroscopy. At 90 K, H₂O molecules are adsorbed on the (2 × 1)-H surface to form ice clusters by the hydrogen-bonding interaction. Four H₂O peaks are observed at 165, 185, 215 and 270 K in the thermal desorption spectra for the ice-covered surface. The peaks at 165 and 185 K correspond to the ice clusters and the peaks at 215 and 270 K to the strongly-bound H₂O species which play a role as the nucleation centers of the ice clusters desorbing as H₂O at 185 and 165 K, respectively.     

CONFORMATIONAL ANALYSIS AND MOLECULAR MODELING OF CHOLESTERIC LIQUID CRYSTAL POLYESTERS BASED ON XRD,RAMAN, AND TRANSITION THERMAL ANALYSIS

Molecular modeling of the cholesteric liquid crystal polyester poly[oxy(1,2 - dodecane)oxycarbonyl-1,4-phenyleneoxycarbonyl-1,4-phenylenecarbonyloxy-1,4-phenylenecarbonyl] (PTOBDME), [C₃₄H₃₆O₈] _n , synthesized in our laboratory and thermally characterized by differential scanning calorimetry (DSC), was performed to explain both its cholesteric mesophase and 3D crystalline structure. Conformational analysis (CA) was run for the monomer both by systematic search and with molecular dynamics (MD) simulations. Minima energy conformers were “polymerized” with Cerius² and helical, cholesteric molecules were obtained in all cases. Our models agree with the chiral behavior observed by X-ray diffraction (XRD), thermooptical analysis (TOA) and circular dichroism (CD) experiments. Crystal packing of the polymer molecules were simulated in cells with parameters a and b obtained from experimental powder X-ray diffraction patterns and c calculated from the translational repetitive unit during the theoretical polymerization. Recalculated X-ray powder diffraction patterns of our models matched the observed ones. Morphology simulation from those crystal models is in good agreement with the crystals observed by optical microscopy. We have also modeled the self-associating nature of those polyesters when dispersed in aqueous media. Simulation of our models surrounded by different solvents, such as water and chloroform, were performed by calculating their interaction energies, coordination numbers, and mixing energies, applying Monte Carlo simulation techniques based on the Flory-Huggins theory. These results were compared with their experimental vibrational Fourier transform (FT)–Raman spectra in the regions in which structural marker bands of the polymer appear.     

EPR investigation of the spin-spin interactions in a Cu(II)-Gd(III)-Fe(III) heterospin system

The spin-spin interactions in a system that contains three different spin carriers, [{LCu}Gd(H₂O)₃×{Fe(CN)₆}] _n ·4nH₂O (1) [L²⁻, N,N-propylenedi(3-methoxysalicylideneiminato)], were investigated by electron paramagnetic resonance spectroscopy. Additional information was obtained by analyzing the discrete heterobinuclear system [LCu(OH₂)Gd(O₂NO)₃] (2), which contains the Cu(II)-Gd(III) pair also existing in the structure of 1, and the compounds [{LCu}Gd(H₂O)₃{Co(CN)₆}] _n ·3.5nH₂O and [{LCu}La(H₂O)₃×{Fe(CN)₆}] _n ·4nH₂O, which are isostructural with 1 and in which the paramagnetic low-spin Fe(III) and Gd(III) ions were replaced by diamagnetic low-spin Co(III) and La(III), respectively. The investigations were carried out in the temperature range of 293–4 K in both X- and Q-bands and also using a dual-mode X-band. The experimental spectra of the Cu(II)-Gd(III) pairs in 2 were interpreted as the sum of spectra of the ground spin state with total S = 4 and the excited state with S = 3 appearing due to the ferromagnetic exchange interaction between Cu(II) and Gd(III) ions. By fitting the experimental and simulated spectra, the zero-field splitting parameters of the Gd(III) ion are estimated and it is shown that no influence of the anisotropic interaction is detected. The magnetic properties of 1 are discussed from the perspective of the interaction of the Cu(II)-Gd(III) binuclear fragments with the Fe(III) ions.     

Broadening of absorption lines of the v2 band of the H2S molecule by the pressure of atmospheric gases

The broadening coefficients γ of absorption lines of the v₂ band of H₂S molecules due to the pressure of molecular gases H₂S (self-broadening), H₂O, N₂, O₂, H₂, D₂, and CO₂ have been calculated by the semiclassical methods. A satisfactory agreement with the experimental data available for some lines has been achieved. In all cases, the parameters of an analytical model allowing the reconstruction of the calculated and experimental values of γ have been determined. For the case of line self-broadening, the calculation has been performed for several temperatures in the range 296 K ≤ T ≤ 1300 K and the parameters determining the temperature dependence of γ have been obtained.     

Infrared Spectra of the Copper(II), Nickel(II) and Palladium(II) Complexes of 4-amino-3-pentene-2-one

Abstract

The infrared spectra of the metal complexes of 4-amino-3-pentene-2-one were measured from 4000 - 20 cm^?1. The absorption bands were assigned by comparison to other similar molecules: The Cu(II) complex of 4-methylamino-3-pentene-2-one, and complexes of acetylacetone. Force constants for the molecules were calculated using the A_xsm matrix method. The spectra were measured at 298^oK and 77^oK.     

Investigation of structural evolution of hydrogen-bond networks of water clusters at 1 and 300 K

Computer simulation of water clusters (H₂O) _n , Na⁺(H₂O) _n and K⁺(H₂O) _n (n ?? 8) at temperatures of 1 and 300 K was carried out using the Monte Carlo method. All the types of the hydrogen-bond network structures at equilibrium configurations of the water clusters and, among them, the most probable ones at temperatures of 1 and 300 K, were detected. The analysis of the most probable types of hydrogen-bond networks at equilibrium configurations of water clusters revealed that clusters with n water molecules inherit the configuration of clusters with n ? 1 water molecules with an accuracy of one hydrogen bond.     

Disorder in ICE VI at 1 GPa: A neutron diffraction study on in situ grown single crystals

Abstract

Crystallographic structure determinations of H₂O and D₂O ice VI single crystals were performed between 207 K and ambient temperautre at pressures of 0.9 GPa. A neutron pressure cell of the Marburg-type was used. Single crystals were grown in situ under optical control in the pressure cell. Details of the cell construction, especially the design of the sapphire anvils and zero-scattering gaskets, are described.     

Equation of state SAFT-CP for vapour–liquid equilibria and mutual solubility of carbon dioxide and water

ABSTRACT

The statistical associating fluid theory (SAFT) was proposed first in 1990, and has been extended to various forms for the calculation of thermodynamic properties of complex systems, such as oil reservoir fluids, polar systems, polymers, electrolytes, near-critical systems, interfacial phenomena, solids and even biomaterials. SAFT-CP (critical point) has been established for nonpolar fluids in 2001 with excellent expression of thermodynamic properties across critical points. It was extended later for polar and associating fluids with the addition of just a dipole–dipole interaction, which leads simple calculation procedure without an association term. In this article SAFT-CP is applied to carbon dioxide, water and their mixture. Vapour–liquid equilibria for pure components CO₂ and H₂O, CO₂ solubility in water and H₂O solubility in dense CO₂ are analysed. Expression of pure CO₂ properties is improved with the dipole–dipole interaction term used, while expression of pure water is a little bit improved with the non-spherical degree parameter less than 1.0. For the high asymmetry in polarity and association between CO₂ and H₂O molecules, the Stryjek–Vera combining rule is used with different temperature-dependent parameters. With the quadratic temperature-dependent parameters, the mutual solubilities in the system are calculated with good agreement with experimental ones over the wide range of temperature as 298–474 K and of pressure as 0.1–70 MPa.     

Ultrasonic study of solid-phase amorphization and polyamorphism in an H2O-D2O (1: 1) solid solution

The elastic moduli and volume of H₂O-D₂O (1: 1) isotopically mixed ice (solid solution) have been studied at the solid-phase amorphization of normal 1h ice under compression at a temperature of 77 K and at the transition from high-density amorphous ice to low-density amorphous ice with subsequent successive crystallization to cubic (1c) and hexagonal (1h) ice at isobaric (0.05 GPa) heating. Comparison of the results with the respective data for H₂O and D₂O ices indicates that the observed concentration (in the isotopic composition) dependences of the elastic moduli and their derivatives for different phases of ice at isotopic hydrogen substitution in the H₂O, H₂O-D₂O (1: 1), and D₂O chain can be both monotonic and significantly nonmonotonic.     

Detection of the structure of the wing of the Rayleigh line in ice, water, and heavy water using four-photon polarization spectroscopy

The spectral structure of the wing of the Rayleigh line in ice, ordinary water (H₂O), and heavy water (D₂O) is recorded in the frequency range 0–50 cm⁻¹ by means of four-photon polarization spectroscopy. It is shown that this structure can be explained by the collective rotational motion of molecules in cells determined by the structure of hexagonal ice. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 1, 12–14 (10 January 1999)     

On the limitation of the van der Waals-Platteeuw-based thermodynamic models for hydrates with multiple occupancy of cavities

Thermodynamic models based on the van der Waals–Platteeuw statistical theory (Adv. Chem. Phys. 2, 1 (1959)) can be very accurate in describing hydrate equilibrium conditions, even for some occasions when multiple cavity occupancy occurs. These are cases outside the range of assumptions used for the development of the original statistical theory. However, during multiple cavity occupancy such models can perform poorly when calculating the cavity occupancies. This paper reports novel Grand Canonical Monte Carlo molecular simulations for the case of pure structure II N₂ hydrate and compares the calculated cavity occupancies with experimental data and observe reasonable agreement. Also examined are the van der Waals–Platteeuw-based modifications that retained the single-occupancy assumption of the original theory and how they perform when predicting cavity occupancies and hydrate equilibrium pressures.     

Reactivity of carbon dioxide at nickel (110)

Adsorption and reactivity of carbon dioxide at the clean and oxygen precovered Ni(110) surface has been studied by means of EELS and LEED. On the clean surface two different types of CO₂ molecules have been observed by EELS at 135 K, one being the undisturbed linear configuration. With increasing temperature the linear molecule changes into a different species which precedes dissociation at 220 K into CO and O. EELS and LEED data of the intermediate species support the assumption that it is a bent CO⁻₂ anion adsorbed in C_2v symmetry with twofold oxygen coordination to the surface. Oxygen preadsorption stabilizes the linear CO₂ molecule up to higher temperatures which does not convert into a bent species in this case. Instead, a reaction product of CO₂ and O is found and interpreted as a carbonate species.     

A difference in the electromagnetic properties of D2O and H2O ice revealed by resonance measurements

The dielectric parameters of H₂O and D₂O ice samples were studied by a resonance technique in the region of 6 GHz. The ratio of the resonance curve halfwidths at half maximum was measured for light and heavy ice in the temperature range from 0 to ?130°C. The temperature dependences of the resonance peak asymmetry of the two types of ice are qualitatively different. The ratio of the higher-frequency halfwidths at half maximum to the lower-frequency one plotted versus temperature exhibits a positive slope for light ice and a negative slope for heavy ice. It is suggested that the difference reflects the different quantum statistics of the hydrogen and deuterium nuclei in ice.     

NEUTRON SCATTERING AND LATTICE DYNAMICAL STUDIES OF THE HIGH-PRESSURE PHASE ICE (I)

Lattice dynamical calculations of ice VIII have been carried out by using a slightly modified set of force constants obtained recently for ice Ih (Li J C and Ross D K 1993 Nature 365 327). A weak interaction was introduced between the two interpenetrated sublattices in the ice VIII structure. The calculated results for H₂O and D₂O ice VIII are in reasonable agreement with the measured inelastic neutron scattering spectra. The eigenvectors of phonon modes in the range of translational and librational bands have been studied in order to understand the properties of the vibrational modes. It is found that the third peak at 26.7meV in the translation results from weak hydrogen bond interactions, and the first peak (14.7meV) is much higher than it is in ice Ih (～7.1meV), which is partially due to the interactions between the two sublattices.     

Calorimetric study of a phase transition in D2O ice Ih doped with KOD: Ice XI

D₂O ice Ih doped with KOD was found by calorimetry to undergo a phase transition at 76 K. The enthalpy and entropy of the phase transition depended in their magnitude on the annealing of the sample. The largest values obtained were ΔH = 155 J mol⁻¹ and δS = 2.06 J K⁻¹ mol⁻¹. The phase transition removed 64% of the residual entropy. Mechanisms of the isotope effect were discussed to explain the difference in the transition temperatures of the D₂O and H₂O ices and compared with the experiment. The pressure coefficient of the transition temperature was calculated by the use of the Clapeyron-Clausius equation and recent data on the molar volume of the new phase. The name ice XI is proposed to designate the ordered phase of ice Ih.