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1.
E. A. Zheligovskaya 《Journal of Structural Chemistry》2008,49(3):459-471
The behavior of structures of H2O crystalline ices Ih, Ic, XI, VII, VIII, VI is studied in molecular dynamics experiment using the potential offered by Poltev and Malenkov. The behavior of the system consisting of one of the two identical interpenetrating, but without any common hydrogen bonds, water frameworks comprising the ice VI structure is also simulated. As a result of simulations, the ice VII structure has collapsed, whereas other systems proved to be stable. The reasons of instability of the ice VII and previously studied ice IV structures in molecular dynamics experiments are discussed. Based on the simulation results of the above-mentioned ices and previous simulation of ices II, III, IX, IV, and XII, the general regularities of dynamic properties of water molecules in crystalline water ices are formulated. Unreliability of results obtained by molecular dynamics in the investigation of self-organizing processes in aqueous systems is shown. 相似文献
2.
Saitta AM Strässle T Rousse G Hamel G Klotz S Nelmes RJ Loveday JS 《The Journal of chemical physics》2004,121(17):8430-8434
The structure of amorphous ice under pressure has been studied by molecular dynamics at 160 K. The starting low-density phase undergoes significant changes as the density increases, and at rho=1.51 g/cm(3) our calculated g(OO)(r) is in excellent agreement with in situ neutron diffraction data obtained at 1.8 GPa and 100 K on very high density amorphous ice made at 150 K. As the system is further compressed, in the theoretical simulations, up to rho=1.90 g/cm(3), the structural modifications are continuous up to the highest density. The analysis of orientational distributions reveals that dense amorphous ice is characterized by major distortions of the tetrahedral geometry, and that the pressure structural changes, already observed experimentally at lower densities, can be interpreted as a trend towards a disordered closed-packed structure. 相似文献
3.
The ability of several water models to predict the properties of ices is discussed. The emphasis is put on the results for the densities and the coexistence curves between the different ice forms. It is concluded that none of the most commonly used rigid models is satisfactory. A new model specifically designed to cope with solid-phase properties is proposed. The parameters have been obtained by fitting the equation of state and selected points of the melting lines and of the coexistence lines involving different ice forms. The phase diagram is then calculated for the new potential. The predicted melting temperature of hexagonal ice (Ih) at 1 bar is 272.2 K. This excellent value does not imply a deterioration of the rest of the properties. In fact, the predictions for both the densities and the coexistence curves are better than for TIP4P, which previously yielded the best estimations of the ice properties. 相似文献
4.
Temperature-dependent deuteron spin lattice relaxation times T(1) have been obtained from water in its three amorphous states at ambient pressure: low density amorphous (LDA), high density amorphous (HDA), and very high density amorphous (VHDA). It is found that in all of these states the magnetization recovery is essentially monoexponential and that T(1) of LDA is significantly longer than that of the higher density forms. Thus, T(1) can be used as a monitor parameter to study the kinetics of the transitions from HDA to LDA and from VHDA to LDA. During the transformation of VHDA to LDA an intermediate state is formed, which, according to its T(1) at low temperature, is clearly determined to be HDA-like. However, and most significantly, the transition from VHDA to this HDA-like state and further on to LDA occurs at temperatures significantly above the kinetic stability limit of native HDA produced at 77 K. These findings contribute to the current discussion on the nature of HDA and VHDA by strengthening the view that the annealing of VHDA at ambient pressure produces a relaxed HDA-like state. 相似文献
5.
The theoretical study of off-resonant fifth-order two-dimensional (2D)-Raman spectroscopy is made to analyze the intermolecular dynamics of liquid and solid water. The 2D-Raman spectroscopy is susceptible to the nonlinear anharmonic dynamics and local hydrogen bond structure in water. It is found that the distinct 2D-Raman response appears as the negative signal near the t(2) axis. The origin of this negative signal for t(2)<15 fs is from the nonlinear polarizability in the librational motions, whereas that for 30 fs相似文献
6.
We have made high density amorphous ice (HDA) by the pressure-induced amorphization of hexagonal ice at 77 K and measured the volume change on isobaric heating in a pressure range between 0.1 and 1.5 GPa. The volume of HDA on heating below ~0.35?GPa increases, while the volume of HDA on heating above ~0.35?GPa decreases. The polarized OH-stretching Raman spectra of the relaxed HDAs are compared with that of the unannealed HDA. The relaxed HDAs are prepared at 0.2 GPa at 130 K and 1.5 GPa at 160 K. It is found that the relatively strong totally symmetric OH-stretching vibration mode around 3100?cm(-1) exists in the depolarized reduced Raman spectrum χ(VH)(") of the unannealed HDA and that its intensity rapidly decreases by relaxation. The χ(VH)(") profiles of the relaxed HDA are similar to those of liquid water. These results indicate that the HDA reaches a nearly equilibrium state by annealing and the intrinsic state of HDA relates to a liquid state. The pressure-volume curve of the relaxed HDA at 140 K seems to be smooth in the pressure range below 1.5 GPa. 相似文献
7.
The kinetics of crystalline ice nucleation and growth in nonporous, molecular beam deposited amorphous solid water (ASW) films are investigated at temperatures near 140 K. We implement an experimental methodology and corresponding model of crystallization kinetics to decouple growth from nucleation and quantify the temperature dependence and absolute rates of both processes. Nucleation rates are found to increase from approximately 3x10(13) m(-3) s(-1) at 134 K to approximately 2x10(17) m(-3) s(-1) at 142 K, corresponding to an Arrhenius activation energy of 168 kJ/mol. Over the same temperature range, the growth velocity increases from approximately 0.4 to approximately 4 A s(-1), also exhibiting Arrhenius behavior with an activation energy of 47 kJ/mol. These nucleation rates are up to ten orders of magnitude larger than in liquid water near 235 K, while growth velocities are approximately 10(9) times smaller. Crystalline ice nucleation kinetics determined in this study differ significantly from those reported previously for porous, background vapor deposited ASW, suggesting the nucleation mechanism is dependent upon film morphology. 相似文献
8.
Z. I. Popov A. S. Fedorov A. A. Kuzubov T. A. Kozhevnikova 《Journal of Structural Chemistry》2011,52(5):861-869
Lithium absorption in silicon is studied at the DFT level. By means of the developed method of modeling the structure of amorphous
silicon, including with impurities, it is shown that with an increase in the lithium concentration intermediate amorphous
Li
x
Si
y
phases, up to the crystalline Li15Si4 phase, form in crystalline silicon. An increase in the silicon cell volume, as it is filled with lithium, is calculated.
A nonlinear dependence of silicon voltage on lithium intercalation is found. The lithium diffusion coefficient in crystalline
silicon at a low lithium concentration is calculated and it is demonstrated for amorphous silicon that lithium diffusion is
substantially accelerated by the lattice deformation inherent in amorphous silicon. The calculated values can be used in the
production of high-capacity lithium ion batteries with a silicon anode. 相似文献
9.
Kinugawa T Yabushita A Kawasaki M Hama T Watanabe N 《Physical chemistry chemical physics : PCCP》2011,13(35):15785-15791
Photodissociation of amorphous ice films of carbon dioxide and water co-adsorbed at 90 K was carried out at 157 nm using oxygen-16 and -18 isotopomers with a time-of-flight photofragment mass spectrometer. O((3)P(J)) atoms, OH (v = 0) radicals, and CO (v = 0,1) molecules were detected as photofragments. CO is produced directly from the photodissociation of CO(2). Two different adsorption states of CO(2), i.e., physisorbed CO(2) on the surface of amorphous solid water and trapped CO(2) in the pores of the film, are clearly distinguished by the translational and internal energy distributions of the CO molecules. The O atom and OH radical are produced from the photodissociation of H(2)O. Since the absorption cross section of CO(2) is smaller than that of H(2)O at 157 nm, the CO(2) surface abundance is relatively increased after prolonged photoirradiation of the mixed ice film, resulting in the formation of a heterogeneously layered structure in the mixed ice at low temperatures. Astrophysical implications are discussed. 相似文献
10.
F Borget T Chiavassa A Allouche F Marinelli J P Aycard 《Journal of the American Chemical Society》2001,123(43):10668-10675
The structure and energy properties of the 1:1 complexes formed between cyanoacetylene and H2O (D2O) are investigated using FT-IR matrix isolation spectroscopy and ab initio calculations at the MP2/ 6-31G(d,p) level. Cyanoacetylene adsorption and desorption on amorphous ice film are monitored by FT-IR using the temperature-programmed desorption method. In an argon matrix, two types of 1:1 complexes are observed. The first one corresponds to the NH structure, which involves a hydrogen bond with the terminal nitrogen of cyanoacetylene. The second corresponds to the HO form, which involves a hydrogen bond from the cyanoacetylene to the oxygen of water. This last complex is the more stable (DeltaE = -8.1 kJ/mol.). As obtained in argon matrixes, two kinds of adsorption site are observed between HC3N and ice. The first one, stable between 25 and 45 K is characterized by a nu(OH) shift similar to the one observed in matrix for the NH complex. The second, stable at higher temperatures (between 45 and 110 K), corresponds to an interaction with the dangling oxygen site of ice and is similar to the HO complex observed in matrix. From theoretical calculations (DFT method combined with a plane wave basis set and ultrasoft pseudopotentials), it is shown that, for this adsorption site, the HC3N moiety is flattened on the ice surface and stabilized by a long-distance interaction ( approximately 3 A) between one dangling OH and the pi system of the C triple bond C triple bond. The HC3N desorption occurs between 110 and 140 K, and the associated desorption energy is 39 kJ/mol. This value is in good agreement with the first principle calculation based on density functional theory and ultrasoft pseudopotentials (34 kJ/mol). These calculations confirm the electrostatic nature of the interaction forces. A small amount of cyanoacetylene is incorporated into the bulk and desorbs at the onset of the ice crystallization near 145 K. In these two kinds of experiments, HC3N acts as both an electrophilic and a nucleophilic molecule. 相似文献
11.
Single water molecules have been isolated in solid Ar matrices at 4 K and studied by rovibrational spectroscopy using FTIR in the regions of the ν(1), ν(2), and ν(3) modes. Upon nuclear spin conversion at 4 K, essentially pure para-H(2)O was prepared, followed by subsequent fast annealing generating ice particles. FTIR studies of the vapor above the condensed water upon annealing to T ≥ 250 K indicate fast reconversion of nuclear spin to equilibrium conditions. Our results indicate that nuclear spin conversion is fast in water dimers and larger clusters, which preclude preparation of concentrated samples of para-H(2)O, such as in ice or vapor. 相似文献
12.
Model structures have been created for ice Ih and for low density (LDA), high density (HDA), and very high density (VHDA) amorphous ices using the procedure for determining the equilibrium configurations of molecules in amorphous phases. The chemical potentials of these ices were calculated for wide ranges of temperature and pressure. The curves of equilibrium phase transitions have been plotted. It is shown that at high pressures, VHDA ice is more stable than Ih, while HDA ice is metastable with respect to VHDA over the whole range of pressures and temperatures. These calculations provide an explanation to the experimentally observed transition of HDA into a higher density phase (VHDA) during isobaric heating. 相似文献
13.
Electronic structures and hydrogen bond network of high-density and very high-density amorphous ices
Electronic structures of hexagonal ice (ice Ih), high-density amorphous ice (HDA), and very high-density amorphous ice (VHDA) are investigated using ab initio density functional theory (DFT) at 77 K under a pressure of 0.1 MPa, focusing on band structure, density of states (DOS), partial density of states (PDOS), and electron density. It is found that the integration intensity of the O-2p bonding band in HDA is 1.53 eV wider than that in the VHDA. Because more 2p electrons in HDA participate the 2p-1s hybridization of O-H. The classical molecular dynamics (MD) method has further been carried out to analyze the hydrogen bond network of HDA and VHDA with larger numbers of water molecules under the same temperature, pressure, and boundary conditions used as those during the DFT calculation. MD results show that there exists some water molecules with five hydrogen bonds in both HDA (4.1 +/- 0.1%) and VHDA (2.8 +/- 0.1%), as compared with the LDA, being consistent with the integration intensity results of PDOS. This result can be used to interpret the physical nature of the similar transition temperature of HDA and VHDA to LDA with different heating rates. 相似文献
14.
Complex shear modulus at 33 kc./sec. is measured at temperatures of ?150–150°C. for amorphous selenium and crystalline selenium with different crystallinities. The dielectric relaxation at 10 kc./sec. to 3 kc./sec. to 3 Mc./sec. is observed at temperatures of ?32–25°C. for iodine-doped crystalline selenium. It is concluded from the results of this study and of others' that selenium exhibits four relaxations, α, β γ, and δ, in order of descending temperature. The β relaxation is observed only in the amorphous sample above the glass temperature and is assigned to the primary relaxation. The α, γ, and δ relaxations are found in the crystalline selenium. The α relaxation, which is prominent in a highly crystalline sample, is assigned to the crystalline relaxation. The γ and δ relaxations increase in peak height with decreasing crystallinity and are attributed to the disordered region in the crystalline selenium. The dispersion map (logarithm of frequency versus reciprocal absolute temperature of loss maximum) of selenium is presented. 相似文献
15.
Isomerization processes of azobenzene dyes dissolved in a glassy polymeric matrix or attached in glassy amorphous or liquid crystalline polymers to the backbone as side groups are induced by light. The isomerization process, in turn, causes the dye to reorient provided that polarized light is used: the long axis of the dye is oriented perpendicular to the polarization direction in the stationary case. Such a reorientation gives rise to strong modifications of the optical properties. This contribution is concerned with the analysis of the correlation between the nature of the azobenzene dyes, the isomerization, reorientation and modulations discussed above and with possible applications in the optical holographic storage. Considered are, in particular, dye/matrix combinations giving rise to nonlinear holographic responses, two photon holography, transient holographic modes applicable for holographic displays and the optical switching of other than optical properties. 相似文献
16.
E. Ferracini A. Ferrero V. Malta S. Martelli W. Vogel 《Colloid and polymer science》1991,269(12):1241-1249
The WAXS powder pattern profile analysis of as-polymerized high-yield isotactic polypropylene has been performed in order to evaluate the crystalline, the so-called amorphous, and the diffuse scattering components. The amorphous component has been interpreted in terms of microcrystallites.The intensity percentages of the sample components are: -crystalline =42.12%, -semimicrocrystalline=18.65%, and -microcrystalline=39.23%. The method allows a good evaluation of the anisotropic structural disorder as well as the crystallite dimensions anisotropy and crystallinity determination. Moreover, the contemporary occurrence of different crystalline modifications in the sample can be defined quantitatively.The crystallinity, expressed as the ratio between the integral intensities diffracted by the large -form crystallites plus the middle-size -form crystallites and the sum of the larger and smaller ones is 61%. 相似文献
17.
Yabushita A Hama T Iida D Kawanaka N Kawasaki M Watanabe N Ashfold MN Loock HP 《The Journal of chemical physics》2008,129(4):044501
The production of H(2) in highly excited vibrational and rotational states (v=0-5, J=0-17) from the 157 nm photodissociation of amorphous solid water ice films at 100 K was observed directly using resonance-enhanced multiphoton ionization. Weaker signals from H(2)(v=2,3 and 4) were obtained from 157 nm photolysis of polycrystalline ice, but H(2)(v=0 and 1) populations in this case were below the detection limit. The H(2) products show two distinct formation mechanisms. Endothermic abstraction of a hydrogen atom from H(2)O by a photolytically produced H atom yields vibrationally cold H(2) products, whereas exothermic recombination of two H-atom photoproducts yields H(2) molecules with a highly excited vibrational distribution and non-Boltzmann rotational population distributions as has been predicted previously by both quantum-mechanical and molecular dynamics calculations. 相似文献
18.
V. Bolis B. Fubini S. Coluccia E. Mostacci 《Journal of Thermal Analysis and Calorimetry》1985,30(6):1283-1292
The surface properties of three SiO2 samples, one crystalline (quartz) and two amorphous, with a large difference in particle size, have been investigated by thermal analysis, adsorption calorimetry and infrared spectroscopy. The variation in the silanol group population upon thermal treatment has been followed via the evolution of the i.r. bands at 3745–3750 cm–1 (free hydroxyl groups) and 3650-3550 cm–1 (adjacent pairs of SiOH) and the evolution of the heat of adsorption of water with coverage on the outgassed samples.The adsorption capacities increase in the sequence high surface area amorphous sample T=673 K) brings about dehydroxylation leaving only isolated silanols on the high surface area amorphous silica, and partial dehydroxylation of the low surface area material. Quartz is totally hydrophilic, as its regular structure probably stabilizes the hydroxyl layers at the surface.
This research was supported by the Ministry of Public Education within a national programme relating to the structure and reactivity of surfaces. 相似文献
Zusammenfassung Die Oberflächeneigenschaften von einer kristallinen (Quarz) und zwei amorphen SiO2-Proben mit großen Unterschieden in der Partikelgröße wurden durch thermische Analyse, Adsorptionskalorimetrie und Infrarotspektroskopie untersucht. Bei thermischer Behandlung eintretende Veränderungen in der Silanolgruppenpopulation wurden durch Messung der IR-Banden bei 3745–3750 cm–1 (freie Hydroxylgruppen) und 3650–3550 cm–1 (benachbarte SiOH-Paare) und der Adsorptionswärme von Wasser an ausgeheitzten Proben untersucht. Die Adsorptionskapazitäten nehmen in folgender Reihenfolge ab: amorphe Probe mit großer Oberfläche > amorphe Probe mit geringer Oberfläche > Quarz. Dehydroxylierung der Oberfläche hat zunehmenden hydrophoben Charakter (Gestalt der Isothermen, Adsorptionswärme kleiner als Kondensationswärme von Wasser) zur Folge. Bei der gleichen thermischen Behandlung (673 K) werden bei amorphen Siliciumdioxid mit großer Oberfläche eine nur isolierte Hydroxylgruppen zurücklassende Dehydroxylierung und bei Material mit kleiner Oberfläche eine teilweise Dehydroxylierung beobachtet. Quarz ist vollkommen hydrophyl, da die reguläre Struktur wahrscheinlich die Hydroxylschichten an der Oberfläche stabilisiert.
, , (), — . 3745–3750 –1 ( ) 3650–3550 –1 ( SiOH), . < < . ( , ). (T=673 K) . , , , .
This research was supported by the Ministry of Public Education within a national programme relating to the structure and reactivity of surfaces. 相似文献
19.
The heat required to release and vaporize bound H2O from crystalline α-lactose monohydrate and from lactose glass, as determined by differential scanning calorimetry is 12.3±0.7 and 10.8±0.5 kcal·mole−1 of H2O, respectively. Water vapor sorption by anhydrous α-lactose leads to the formation of the α-monohydrate. The isotherm, obtained gravimetrically for this process is Langmuir type. β-Lactose is completely non-hygroscopic below 97% relative humidity. Thereafter, it sorbs H2O rapidly to form a concentrated solution wherein the lactose is capable of mutarotation. Densites of lactose forms determined pycnometrically by helium displacement are: 1.535 g/cm3 for α-lactose·H2O; 1.547 g/cm3 for anhydrous α-lactose; and 1.576 g/cm3 for β-lactose. 相似文献
20.
Burke DJ Wolff AJ Edridge JL Brown WA 《Physical chemistry chemical physics : PCCP》2008,10(32):4956-4967
Despite considerable attention in the literature being given to the desorption behaviour of smaller volatiles, the thermal properties of complex organics, such as ethanol (C(2)H(5)OH), which are predicted to be formed within interstellar ices, have yet to be characterized. With this in mind, reflection absorption infrared spectroscopy (RAIRS) and temperature programmed desorption (TPD) have been used to probe the adsorption and desorption of C(2)H(5)OH deposited on top of water (H(2)O) films of various thicknesses grown on highly oriented pyrolytic graphite (HOPG) at 98 K. Unlike many other molecules detected within interstellar ices, C(2)H(5)OH has a comparable sublimation temperature to H(2)O and therefore gives rise to a complicated desorption profile. RAIRS and TPD show that C(2)H(5)OH is incorporated into the underlying ASW film during heating, due to a morphology change in both the C(2)H(5)OH and H(2)O ices. Desorption peaks assigned to C(2)H(5)OH co-desorption with amorphous, crystalline (CI) and hexagonal H(2)O-ice phases, in addition to C(2)H(5)OH multilayer desorption are observed in the TPD. When C(2)H(5)OH is deposited beneath ASW films, or is co-deposited as a mixture with H(2)O, complete co-desorption is observed, providing further evidence of thermally induced mixing between the ices. C(2)H(5)OH is also shown to modify the desorption of H(2)O at the ASW-CI phase transition. This behaviour has not been previously reported for more commonly studied volatiles found within astrophysical ices. These results are consistent with astronomical observations, which suggest that gas-phase C(2)H(5)OH is localized in hotter regions of the ISM, such as hot cores. 相似文献