Structure of ice

Water ices play a critical role in various astrophysical phenomena and store information about the thermal history of icy grains. To understand this history, clarifying the formation conditions in astrophysical environments is critical. In addition to taking the form of amorphous ices, ice can take four crystalline forms: hexagonal ice I (ice Ih), cubic ice I (ice Ic) and hydrogen-ordered hexagonal ice (ice XIh) and cubic ice (ice XIc). The aim of this article is to study the conditions for phase transitions among these different crystalline ices. We found through cryogenic transmission electron microscopy observations that some polymorphs of ice XIh were formed by simple annealing of ice Ih at 120–150 K without any dopant or irradiation. We also investigated the formation conditions of ice Ih by vapour deposition and heating of ice Ic in protoplanetary discs. The transition kinetics from ice Ih to ice XIh suggested that ice XIh exists between the transition temperature from ice Ic to ice Ih and 150 K. From these results, we constructed a water-vapour flux–temperature–time diagram that clarifies the amorphous, Ic, Ih, XIc and XIh ice phases. We found that, under the conditions encountered in most protostars, hydrogen-ordered ices XIh and XIc can exist just outside the snow line and below 125 K, respectively. The infrared libration modes should enable these phases to be distinguished observationally. Because some of these phases are chiral, their presence could fundamentally affect the evolution of other homochiral organic molecules that develop on their surface.

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.

view Abstract Citations (157) References (75) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS High-Density Amorphous Ice, the Frost on Interstellar Grains Jenniskens, P. ; Blake, D. F. ; Wilson, M. A. ; Pohorille, A. Abstract Most water ice in the universe is in a form which does not occur naturally on Earth and of which only minimal amounts have been made in the laboratory. We have encountered this "high-density amorphous ice" in electron diffraction experiments of low-temperature (T < 30 K) vapor-deposited water and have subsequently modeled its structure using molecular dynamics simulations. The characteristic feature of high-density amorphous ice is the presence of "interstitial" oxygen pair distances between 3 and 4 A. However, we find that the structure is best described as a collapsed lattice of the more familiar low-density amorphous form. These distortions are frozen in at temperatures below 38 K because, we propose, it requires the breaking of one hydrogen bond, on average, per molecule to relieve the strain and to restructure the lattice to that of low-density amorphous ice. Several features of astrophysical ice analogs studied in laboratory experiments are readily explained by the structural transition from high-density amorphous ice into low-density amorphous ice. Changes in the shape of the 3.07 microns water band, trapping efficiency of CO, CO loss, changes in the CO band structure, and the recombination of radicals induced by low-temperature UV photolysis all covary with structural changes that occur in the ice during this amorphous to amorphous transition. While the 3.07 microns ice band in various astronomical environments can be modeled with spectra of simple mixtures of amorphous and crystalline forms, the contribution of the high-density amorphous form nearly always dominates. Publication: The Astrophysical Journal Pub Date: January 1995 DOI: 10.1086/176585 Bibcode: 1995ApJ...455..389J Keywords: INFRARED: ISM: LINES AND BANDS; ISM: DUST; EXTINCTION; ISM: MOLECULES; LINE: PROFILES; MOLECULAR DATA; METHODS: LABORATORY; Density (Mass/Volume); Amorphous Materials; Ice; Frost; Interstellar Matter; Astronomy; Astrophysics; Cosmic Dust; Crystallinity; Electron Diffraction; Hydrogen Bonds; Molecular Dynamics; Radicals; Shapes; Trapping; Universe; Vapor Deposition; Water; Astrophysics full text sources ADS |

The transitions of the recovered high-pressure phase ice VIII first to high-density amorphous (hda) and low-density amorphous ices, and finally to cubic Ic, and hexagonal Ih ice were observed at heating using real-time neutron diffraction. Inelastic incoherent neutron scattering measurements on the hdu ice, ice Ih and high-pressure phase ice VI revealed similarity between the amorphous phase and crystalline ice VI and led to the new proposition that hda ice consists of two interpenetrating hydrogen-bounded networks with no hydrogen bonds between “sublattices”.

Similarity of vibrational spectra of high-density amorphous ice and high-pressure phase ice VI

High sensitivity temperature-programmed desorption mass spectrometry (TPDMS) was employed in order to investigate the desorption kinetics of CCl4 from thin (∼500 ML (ML: monolayer)) amorphous D2O ice films. TPDMS experiments demonstrate that at low coverages CCl4 is trapped in the pores near the surface of microscopically rough ice. Three distinct desorption features, μ-, δ-, and ε-CCl4, consistent with the release of trapped CCl4 were observed. The μ-, δ-, and ε-CCl4 desorption yields demonstrate high sensitivity to the temperature and rate of ice film deposition. We interpret these results as evidence of the existence of three metastable forms of microporous amorphous ice, Iμ, Iδ, and Iε. Measurements of the relative desorption yields from CCl4 species trapped at the surface of ice films prepared at different temperatures and deposition rates were used in order to estimate the barriers to the diffusion of D2O on the surface of Iδ (EDδ) and Iε (EDε). The values obtained were EDδ = 5 ± 1 kcal mol-1 and EDε = 9 ± 2 kcal mol-1. We suggest that Iμ, Iδ, and Iε can be characterized respectively by the relative abundances of two-, three-, and four-coordinated D2O molecules at the ice surface. A proposed phase diagram for thin D2O ice films is presented.

Ice-nucleating proteins (INPs) are a unique class of biological macromolecules that catalyze the freezing of supercooled water with remarkable efficiency, exceeding that of most other known heterogeneous nucleators. Their exceptional efficiency has motivated applications across diverse sectors, including agricultural frost protection, food processing and packaging, biomedical cryopreservation, and even strategies for mitigating glacier ice loss. The ice-nucleation performance of INPs and the mechanical behavior of the ice they produce depend strongly on their structural and biochemical characteristics. However, the links between INP properties, the resulting ice microstructure, and their mechanical behavior have yet to be systematically established. In this study, coarse-grained molecular dynamics (CGMD) simulations using the machine-learned ML-BOP potential are employed to investigate how varying INP configurational parameters, including INP length and number of INPs, influence the ice-nucleation temperature, the resulting ice microstructure, and the mechanical behavior of the formed ice under creep tensile loading. We find that, depending on the length and number of INPs, they can significantly raise the ice-nucleation rate while altering the grain structure of ice. Our simulations reveal that INP-assisted nucleation leads to faster stabilization of the resulting polycrystalline ice composed of hexagonal ice (ice Ih) and cubic ice (ice Ic) as compared to nucleation in pure water. Moreover, a higher number of INPs and smaller ice grain sizes reduce the overall yield stress, while promoting diffusion-accommodated grain boundary sliding creep. These findings provide molecular-level insights into how INPs influence both the nucleation process and the mechanical behavior of ice, highlighting a pathway to engineer ice with tailored stability for real-world settings, including human activities and infrastructure in polar and icy environments.

The heat capacities of the glassy and liquid states of three lithium chloride aqueous solutions (LiCl⋅4H2O,LiCl⋅6H2O,LiCl⋅7.5H2O) were measured with an adiabatic calorimeter in the temperature range 5–340 K; the crystalline state was also measured for LiCl⋅4H2O. For all of the glassy samples, a large non-Debye excess heat capacity appeared below 30 K. The neutron scattering spectra of glassy LiCl⋅4H2O and LiCl⋅6H2O were measured with two spectrometers operating with different energy windows (E&amp;lt;20 meV and E&amp;lt;100 meV). A boson peak, corresponding to the excess heat capacity, appeared at around 4 meV in the S(Q,E) spectra of both glassy samples. From the analysis combining the heat capacity and neutron scattering data, the excess density of states due to the boson peak (compared with hexagonal ice) was found to be 0.10 degree of freedom per water molecule for both glassy samples. A librational peak of water molecules appeared at around 60 meV in glassy samples. This energy is about 10 meV lower than that of hexagonal and amorphous ices, indicating that the hydrogen bonds connecting water molecules are broken due to the strong coordination of water molecules to lithium ions.

The 90 K polarized Raman scattering of thin films of ice Ic and ice Ia containing mixtures of intact H2O and D2O have been measured using the interference-enhanced internal-reflection technique. The effects of isotopic dilution reported for samples with a D2O content ranging from 0% to 100% are consistent with the commonly held view that intermolecular coupling produces collective vibrational modes that determine the appearance of the Raman spectra in the stretching mode region of crystalline and amorphous ice. The convergence of bands produced by the collective modes on the isotopically decoupled mode frequencies of both ν1 and ν3 is displayed in this study. Bands at 3323 and 3209 cm−1 in the anisotropic scattering of protiated ice Ic are shown to converge on the decoupled antisymmetric stretch frequency of 3370 cm−1. The gradual shift of the dominant isotropic scattering at 3085 cm−1 towards the frequency of the decoupled ν1 mode is also revealed, with bands for the first stage in the evolution of the in-phase ν1 collective mode, i.e., the neighbor coupled mode, observed at 3180 (H2O) and 2340 cm−1 (D2O). The data also suggest that the shift of the in-phase coupled ν1 band begins with the first traces of added diluent, a behavior that indicates a macroscopic extension of the resonant coupling for both crystalline and amorphous ice. By contrast, the insensitivity of isotropic scattering near 3420 cm−1 to isotopic dilution suggests that the overtone of the bending mode is the likely source.

Context. Thermal inertias of atmosphereless icy planetary bodies happen to be very low.Aims. We relate the thermal inertia to the regolith properties such as porosity, grain size, ice form and heat transfer processes to understand why it is low. We interpret the dichotomy in thermal inertia of the surface of Mimas in terms of changes in regolith properties. We predict how the thermal inertia of these bodies may vary with heliocentric distance depending on these properties.Methods. We combine available models of conductivity by contact or radiation to understand what heat transfer process is predominant.Results. The magnitude of the thermal inertia of a porous icy regolith is mainly governed by the crystalline or amorphous ice forms, and the quality of contacts between grains. Beyond the orbit of Jupiter, thermal inertias as low as a few tens J/m2 / K/s1/2 are difficult to reproduce with plausible porosity and grains sizes made of crystalline ice unless contacts are loose. This is, on the contrary, straightforward for regoliths of sub-cm-sized grains made of amorphous water ice. This study points out the importance of including the temperature dependence of thermophysical properties of water ice forms and the radiative conduction in thermal models of these bodies. The relatively high thermal inertia of the leading face of Mimas can be explained by a regolith of crystalline ice grains in tight contacts, which are eventually sintered by the bombardment of high energy electrons. The low thermal inertia of its trailing face is easily reproduced by a regolith of moderate porosity with sub-mm-sized grains of amorphous ice. The characteristic decrease of thermal inertia with heliocentric distance of icy atmosphereless surfaces and the very low thermal inertia of relevant trans-Neptunian objects are easily explained if amorphous ice is present at cm depths below a thin layer of crystalline ice.

Adsorption of N 2 and CO 2 on ice

A detailed assignment of the infrared and Raman O–H stretching bands of disordered ice Ih and Ic is proposed. It is based on the assumptions that the spectra of disordered ice Ic are closely related to those of ordered ice Ic, and that the spectra of the as yet unrealized ordered ice Ic can be predicted from the spectra of ice VIII. The supposed similarity between the spectra of ordered and disordered ice Ic is justified by the observed similarity of the spectra of ice VIII and VII, which are respectively ordered and disordered forms of the same structure and are closely related to ordered and disordered ice Ic. The assignment takes into account the intermolecular coupling, which is particularly strong for the ν1 vibrations but weak for the v3, and the TO–LO splitting, particularly of the v3 vibrations, which is shown to be required by the high infrared intensity. The infrared and Raman bands of amorphous ice have been assigned by analogy with the assignments of ice I.

The adsorption of HCN at the surface of low-density amorphous (LDA) ice and its dissolution in the bulk LDA phase is studied by grand canonical Monte Carlo (GCMC) simulations at the temperatures of 50, 100, and 200 K, characteristic of different domains of the interstellar medium (ISM). Dissolved and adsorbed molecules are distinguished using the identification of the truly interfacial molecules (ITIM) method. The results reveal that the adsorption is monomolecular and the adsorption monolayer is only partially saturated at the point of condensation of HCN. The surface coverage corresponding to the saturated adsorption monolayer is estimated to be 9.8 ± 0.3 μmol/m2, providing a better estimate for this quantity than the crude approximation used in evaluating certain experiments. For the entropy of the condensed (glassy) phase of HCN, the simulations provide the value of 17.37 J/(mol K). The adsorption isotherms deviate considerably from the Langmuir shape, revealing that non-negligible interaction occurs between the adsorbed HCN molecules. The adsorption is found to be primarily governed by the dipolar interactions both between the surface water and adsorbed HCN molecules and between HCN neighbors within the adsorption layer. The heat of adsorption at infinitely low surface coverage is estimated to be −49.4 ± 3.9 kJ/mol. Further, the isosteric heat of adsorption at finite coverages is calculated in the entire range of surface coverages. In clear contrast with the adsorption, the dissolution of the HCN molecules remains ideal up to the point of condensation. This indicates that, in spite of the surprisingly large HCN concentrations reached, the HCN–HCN interaction is negligible in the bulk LDA phase. Further, contrary to its adsorption, the dissolution of HCN in LDA ice turns out to be an endothermic process. Finally, our results concerning the adsorption of HCN are not incompatible with the possibility of the oligomerization reaction of the HCN molecules, leading to the prebiotic formation of certain building blocks of biological macromolecules, under interstellar conditions at the LDA surface. Further, assuming that upon approaching the Earth, the transformation of the LDA phase with increasing temperature to liquid water goes through the thermodynamically stable crystalline (Ih) ice phase, which does not dissolve HCN molecules, the presumed expulsion of HCN to the ice surface could provide an additional window of opportunity for their oligomerization.

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionCorrection to "CH3O Radical Binding on Hexagonal Water Ice and Amorphous Solid Water"W. M. C. Sameera*W. M. C. SameeraInstitute of Low Temperature Science, Hokkaido University, N19-W8, Kita-ku, Sapporo, Hokkaido 060-0819, Japan*Email: [email protected]. Tel.: +81-11-706-7449. Fax: +81-11-706-7142.More by W. M. C. Sameerahttps://orcid.org/0000-0003-0213-0688, Bethmini SenevirathneBethmini SenevirathneDepartment of Chemistry and Molecular Biology, University of Gothenburg, Kemigården 4, SE-412 96 Gothenburg, SwedenMore by Bethmini Senevirathne, Stefan AnderssonStefan AnderssonDepartment of Chemistry and Molecular Biology, University of Gothenburg, Kemigården 4, SE-412 96 Gothenburg, SwedenSINTEF Industry, P.O. Box 4760 Torgarden, NO-7465 Trondheim, NorwayMore by Stefan Andersson, Muhsen Al-IbadiMuhsen Al-IbadiDepartment of Chemistry, College of Science, University of Kufa, P.O 21, Najaf, IraqMore by Muhsen Al-Ibadi, Hiroshi HidakaHiroshi HidakaInstitute of Low Temperature Science, Hokkaido University, N19-W8, Kita-ku, Sapporo, Hokkaido 060-0819, JapanMore by Hiroshi Hidaka, Akira KouchiAkira KouchiInstitute of Low Temperature Science, Hokkaido University, N19-W8, Kita-ku, Sapporo, Hokkaido 060-0819, JapanMore by Akira Kouchi, Gunnar NymanGunnar NymanDepartment of Chemistry and Molecular Biology, University of Gothenburg, Kemigården 4, SE-412 96 Gothenburg, SwedenMore by Gunnar Nymanhttps://orcid.org/0000-0002-9527-3890, and Naoki WatanabeNaoki WatanabeInstitute of Low Temperature Science, Hokkaido University, N19-W8, Kita-ku, Sapporo, Hokkaido 060-0819, JapanMore by Naoki Watanabehttps://orcid.org/0000-0001-8408-2872Cite this: J. Phys. Chem. A 2024, 128, 7, 1397Publication Date (Web):February 13, 2024Publication History Received24 January 2024Published online13 February 2024Published inissue 22 February 2024https://doi.org/10.1021/acs.jpca.4c00513Copyright © 2024 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissions This publication is free to access through this site. Learn MoreArticle Views148Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail PDF (811 KB) Get e-Alertsclose Get e-Alerts

Amorphous TiO2 nanotubes with diameters of 8-10 nm and length of several nanometers were synthesized by high pressure treatment of anatase TiO2 nanotubes. The structural phase transitions of anatase TiO2 nanotubes were investigated by using in-situ high-pressure synchrotron X-ray diffraction (XRD) method. The starting anatase structure is stable up to ∼20GPa, and transforms into a high-density amorphous (HDA) form at higher pressure. Pressure-modified high- to low-density transition was observed in the amorphous form upon decompression. The pressure-induced amorphization and polyamorphism are in good agreement with the previous results in ultrafine TiO2 nanoparticles and nanoribbons. The relationship between the LDA form and α-PbO2 phase was revealed by high-resolution transmission electron microscopy (HRTEM) study. In addition, the bulk modulus (B0 = 158 GPa) of the anatase TiO2 nanotubes is smaller than those of the corresponding bulks and nanoparticles (180-240 GPa). We suggest that the unique open-ended nanotube morphology and nanosize play important roles in the high pressure phase transition of TiO2 nanotubes.