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Ice is known to collapse to amorphous ice upon pressurization at low temperatures and shows the unusual feature of multiple distinct solid amorphous water states, which have inspired models of liquid water’s structure and unusual properties. Here, we use heat capacity Cp measurements to show that similarly collapsed ice clathrates display identical glass behavior as amorphous ice but that crystallization above the glass transition temperature Tg of ∼140 K at 1 GPa is inhibited. This effect of the homogeneously distributed “guest molecules” in water reveals a relatively strong reversible Cp increase above Tg but no further transition before crystallization at ∼190 K. This is consistent with a glass–liquid transition of water at Tg, which suggests a new path to study an ultraviscous liquid water network and evaluate water models.

Saturn’s satellite Phoebe is the best-characterized representative of large outer Solar System planetesimals, thanks to the close flyby by the Cassini spacecraft in June 2004. We explore the information contained in Phoebe’s physical properties, density and shape, which are significantly different from those of other icy objects in its size range. Phoebe’s higher density has been interpreted as evidence that it was captured, probably from the proto-Kuiper-Belt. First, we demonstrate that Phoebe’s shape is globally relaxed and consistent with a spheroid in hydrostatic equilibrium with its rotation period. This distinguishes the satellite from ‘rubble-piles’ that are thought to result from the disruption of larger proto-satellites. We numerically model the geophysical evolution of Phoebe, accounting for the feedback between porosity and thermal state. We compare thermal evolution models for different assumptions on the formation of Phoebe, in particular the state of its water, amorphous or crystalline. We track the evolution of porosity and thermal conductivity as well as the destabilization of amorphous ice or clathrate hydrates. While rubble-piles may never reach temperatures suitable for porous ice to creep and relax, we argue that Phoebe’s shape could have relaxed due to heat from the decay of 26Al, provided that this object formed less than 3 Myr after the production of the calcium–aluminum inclusions. This is consistent with the idea that Phoebe could be an exemplar of planetesimals that formed in the transneptunian region and later accreted onto outer planet satellites, either during the satellite’s formation stage, or still later, during the late heavy bombardment.

International audience; A five-dimensional intermolecular potential for H2O-D-2 was obtained from the full nine-dimensional ab initio potential surface of Valiron et al. [P. Valiron, M. Wernli, A. Faure, L. Wiesenfeld, C. Rist, S. Kedzuch, J. Noga, J. Chem. Phys. 129 (2008) 134306] by averaging over the ground state vibrational wave functions of H2O and D-2. On this five-dimensional potential with a well depth D-e of 232.12 cm (1) we calculated the bound rovibrational levels of H2O-D-2 for total angular momentum J = 0-3. The method used to compute the rovibrational levels is similar to a scattering approach-it involves a basis of coupled free rotor wave functions for the hindered internal rotations and the overall rotation of the dimer-while it uses a discrete variable representation of the intermolecular distance coordinate R. The basis was adapted to the permutation symmetry associated with the para/ortho (p/o) nature of both H2O and D-2, as well as to inversion symmetry. As expected, the H2O-D-2 dimer is more strongly bound than its H2O-H-2 isotopologue [cf. A. van der Avoird, D. J. Nesbitt, J. Chem. Phys. 134 (2011) 044314], with dissociation energies D-0 of 46.10, 50.59, 67.43, and 73.53 cm (1) for pH(2)O-oD(2), oH(2)O-oD(2), pH(2)O-pD(2), and oH(2)O-pD(2). A rotationally resolved infrared spectrum of H2O-D2 was measured in the frequency region of the H2O bend mode. The ab initio calculated values of the rotational and distortion constants agree well with the values extracted from this spectrum.

The nature of cometary volatile materials is subject to debate. Theoretical models of cometary nuclei and laboratory studies suggest that these objects could be made of amorphous water ice in addition to other volatile molecules and refractory grains. This water ice structure has the ability to encapsulate the gases of surrounding environment, reflecting the physical and chemical conditions during their deposition. Therefore, the knowledge of the chemical composition of volatile molecules trapped in amorphous water ice provides a tool for probing the formation environment of cometary ice grains. Experimental studies of gas trapping efficiency in amorphous water ice have been previously conducted mostly under kinetic conditions, where dynamic pumping and temperature gradients prevented rigorous calibrations. In this work, we investigated the trapping efficiencies of Ar, CO, CH4, Kr and N2 by depositing water vapor as ice in the presence of trace gases in a volume submerged in liquid nitrogen at 77 K. The gas trapping efficiencies were determined simply by monitoring the pressure difference of the trace gases before and after the deposition of a known amount of water molecules as amorphous ice. Our results show that the trapped gas to water molecule ratio in amorphous ice is controlled primarily by the partial pressure of the gas during water ice deposition, and is independent of the ice deposition rate as well as the gas to water ratio in the vapor phase. The trapping efficiencies of gases decrease in the order of Kr > CH4 > CO > Ar > N2 in accordance with previous studies. Assuming that the water ice structure of comets is at least partially amorphous water ice at the time of their formation, these results suggest that the total pressure and composition of the surrounding environment of amorphous ice formation are significant controlling factors of trace gas concentrations in cometary ice. This further indicates that the evolution of the solar nebula and timing of cometary ice condensation can also be important parameters in linking the volatile contents of comets and their formation process.

Change in the state of water sorbed into four kinds of non-water-soluble poly(meth)acrylates with low water content by temperature (T) perturbation was examined on the basis of T variable mid-infrared (MIR) spectroscopy. Many studies using differential scanning calorimetry suggested that there was no change in the state. T dependence of their MIR spectra, however, clearly demonstrated various changes in the state. Furthermore, recrystallization, which was crystallization during heating, was observed in all four polymers. The recrystallization observed in this study was not devitrification, which is the change in the state from glassy water to crystalline water, but vapor deposition during heating (vapor re-deposition). There were only two reports about recrystallization of water in a non-water-soluble polymer before this report; therefore, it might be considered to be a rare phenomenon. However, as demonstrated in this study, it is not a rare phenomenon. Recrystallization (vapor re-deposition) of water in the polymer matrices is related to a balance between flexibility and strength of the electrostatic interaction sites of polymer matrices but might not be related to the biocompatibility of polymers.

The freezing of water to ice is fundamentally important to fields as diverse as cloud formation to cryopreservation. At ambient conditions, ice is considered to exist in two crystalline forms: stable hexagonal ice and metastable cubic ice. Using X-ray diffraction data and Monte Carlo simulations, we show that ice that crystallizes homogeneously from supercooled water is neither of these phases. The resulting ice is disordered in one dimension and therefore possesses neither cubic nor hexagonal symmetry and is instead composed of randomly stacked layers of cubic and hexagonal sequences. We refer to this ice as stacking-disordered ice I. Stacking disorder and stacking faults have been reported earlier for metastable ice I, but only for ice crystallizing in mesopores and in samples recrystallized from high-pressure ice phases rather than in water droplets. Review of the literature reveals that almost all ice that has been identified as cubic ice in previous diffraction studies and generated in a variety of ways was most likely stacking-disordered ice I with varying degrees of stacking disorder. These findings highlight the need to reevaluate the physical and thermodynamic properties of this metastable ice as a function of the nature and extent of stacking disorder using well-characterized samples.

The structure of ice samples formed in the decay of a water impurity gel at temperatures above 4 K and atmospheric pressure has been examined. The X-ray diffraction analysis indicates that three phases coexist in the initial sample at temperatures of 85–110 K. These phases are amorphous ice occupying up to 30% of the sample volume, cubic-phase ice I c metastable at low pressures (∼60%), and normal hexagonal ice I h (≤6%). The characteristic sizes of crystals of the cubic and hexagonal phases are about 6 and 30 nm, respectively. The amorphous phase at annealing above 110 K is gradually transformed to the crystalline phase both cubic and hexagonal. This transition is accompanied by two processes, including a fast increase in the sizes of cubicphase nanocrystals and the partial transition of the cubic phase I c to the hexagonal one I h. Hexagonal ice I h prevails in the bulk of the sample above 200 K.

Noctilucent clouds and polar mesospheric summer echoes are both manifestations of ice particles near the summer polar mesopause. These ice particles are believed to form mainly on pre-existing ice condensation nuclei. The characteristics and especially the concentrations of such nuclei have been considered important factors in determining ice properties. More ice condensation nuclei would, given the limited amount of water vapor, yield more but smaller ice particles, and thus a dimmer noctilucent cloud. However, here it is shown that the sensitivity of observable ice properties to condensation nuclei concentration is much less than one would expect from the simple situation described above. In particular, both ice mass and cloud brightness is close to independent of condensation nuclei concentration. The reason for this lack of sensitivity is further examined.

The X-ray pattern of ice recorded at −10°C reveals, along with the reflexes of a hexagonal phase, intense diffuse X-ray scattering, testifying to the presence of a noncrystalline phase in the sample. Heating of ice to a temperature close to the melting point leads to almost complete decomposition of the crystalline phase. As this takes place, intense diffuse X-ray scattering with a maximum at 2Θ of 23°C appears in the diffraction pattern, which is typical for a metastable amorphous phase. The first maximums of the radial distribution function for the metastable amorphous phase of ice appear to be close in their positions to the first radii of the hexagonal phase coordination spheres.

Small ice crystals are critical to ice cream quality and shelf life. In a scraped-surface freezer, ice crystals nucleate on the wall where the temperature is the coldest. The scraper blade then transports these crystals, in a layer of slush, to the warmer bulk zone of the freezer. Understanding the formation of ice crystals in a scraped-surface freezer will aid in retaining small ice crystals in ice cream. By freezing and warming thin layers of ice cream mix on a temperature-controlled microscope slide, it was found that warmer freezing temperatures gave more elongated and slightly larger crystals with a wider size distribution. Warming the crystals faster produced smaller or rounder ice crystals, depending on the residence time. These results suggest that, other variables being equal, freezers designed to quickly warm the scraped slush layer from its wall temperature to the bulk temperature may produce ice cream with smaller ice crystals.

Backscattering of very low energy electrons in thin layers of amorphous ice is known to provide experimental data for the elastic and inelastic cross sections and indicates values to be expected in liquid water. The extraction of cross sections was based on a transport analysis consistent with Monte Carlo simulation of electron trajectories. However, at electron energies below 20 eV, quantum coherence effects may be important and trajectory-based methods may be in significant error. This possibility is here investigated by calculating quantum multiple elastic scattering of electrons in a simple model of a very small, thin foil of amorphous ice.The average quantum multiple elastic scattering of electrons is calculated for a large number of simulated foils, using a point-scatterer model for the water molecule and taking inelastic absorption into account. The calculation is compared with a corresponding trajectory simulation.The difference between average quantum scattering and trajectory simulation at energies below about 20 eV is large, in particular in the forward scattering direction, and is found to be almost entirely due to coherence effects associated with the short-range order in the amorphous ice. For electrons backscattered at the experimental detection angle (45° relative to the surface normal) the difference is however small except at electron energies below about 10 eV.Although coherence effects are in general found to be strong, the mean free path values derived by trajectory-based analysis may actually be in fair agreement with the result of an analysis based on quantum scattering, at least for electron energies larger than about 10 eV.

Although the melting of ice is an everyday process, important issues remain unclear particularly on the nanoscale. Indeed despite extensive studies into ice melting and premelting, little is known about the relationship between (pre)melting and crystal size and morphology, with, for example, the melting temperature of ice nanocrystals being unclear. Here we report extensive long-time force-field-based molecular dynamics studies of the melting of hexagonal ice nanocrystals in the ca. 2 to 8 nm size range. We show that premelting is initiated at the corners of the crystals, then the edges between facets, and then the flat surfaces; that is, the melting temperature is related to the degree of coordination. A strong size dependence of the melting temperature is observed, with the combination of small particle size and premelting leading nanosized ice crystals to have liquid-like surfaces as low as about 130 K below the bulk ice melting temperature. These results will be of relevance in understanding the size dependence of ice crystal morphology and the surface reactivity of ice particles under atmospheric conditions.

This work is a continuation of our previous paper about brightening of Comet 17P/Holmes (Kossacki, K.J., Szutowicz, S. [2010]. Icarus 207, 320–340). In that paper we presented results of simulations indicating that the nonuniform crystallization of amorphous water ice itself is probably not sufficient for an explosion. In the present work we investigate the possibility that the explosion is caused by a rapid sublimation of the CO ice leading to the rise of gas pressure above the tensile strength of the nucleus. We simulated evolution of a model nucleus in the orbit of Comet 17P/Holmes. The nucleus is composed of water ice, carbon monoxide ice and dust and has the shape of an elongated ellipsoid. The simulations include crystallization of amorphous ice in the nucleus, changes of the dust mantle thickness, and sublimation of the CO ice. In our model CO is mantling grains composed of dust and amorphous water ice. Orientation of the nuclear spin axis in space is the same as derived in Moreno et al. (Moreno, F., Ortiz, J.L., Santos-Sanz, P., Morales, N., Vidal-Nunez, M.J., Lara, L.M., Gutierrez, P.J. [2008]. Astrophys. J. 677, L63–L66) for Comet Holmes during recent brightening event. Hence, the angle between the orbital and the equatorial planes of the comet is I = 95°, and the cometocentric solar longitude at perihelion is Φ = 210°. The calculations are performed for the south pole being the sub-solar point close to time of the outburst. Our computations indicate, that the CO pressure within the comet nucleus can rise to high values. When the layer between the dust mantle and the crystallization front of the amorphous water ice is very fine grained, few microns in radius, the CO pressure within the nucleus can exceed 10 kPa. This value is the lowest estimate for the tensile strength of the nucleus of Comet Holmes (Reach, W.T., Vaubaillon, J., Lisse, C.M., Holloway, M., Rho, J. [2010]. Icarus 208, 276–292). Hence, when the gas pressure reaches this value the nucleus may explode.

We investigate thermodynamic properties of supercooled water across the “no man’s land” onto the formation of amorphous ice. The calculations are aided by very long computer simulations, often more than 50 μs long, with the TIP4P/2005 model potential. Density fluctuations that arise from the proximity to a putative liquid-liquid (LL) transition at 228 K, cast a long shadow on the properties of water, both above and below the LL transition. We carry out the calculations of the quantum mechanical static and frequency-dependent specific heats by combining seminal studies of Lebowitz, Percus, and Verlet and Grest and Nagel with the harmonic approximation for the density of states. The obtained values are in quantitative agreement with all available experimental and numerical results of specific heats for both supercooled water and ice. We calculate the entropy at all the state points by integrating the specific heat. We find that the quantum corrected-contributions of intermolecular vibrational entropy dominate the excess entropy of amorphous phases over the crystal over a wide range of temperatures. Interestingly, the vibrational entropy lowers the Kauzmann temperature, TK, to 130 K, just below the experimental glass-to-liquid water transition temperature, Tg, of 136 K and the calculated Tg of 135 K in our previous study. A straightforward extrapolation of high temperature entropy from 250 K to below however would give a much higher value of TK ∼ 190 K. The calculation of Lindemann ratios shows the melting of amorphous ice ∼135 K. The amorphous state exhibits an extremely short correlation length for the distance dependence of orientational correlation.

We have studied the influence of sodium ions bound near the ice/vacuum interface on the electron solvation dynamics in amorphous D2O ice layers by means of femtosecond time-resolved two-photon photoelectron spectroscopy. Adsorption of submonolayer coverages of sodium on top of multilayers of amorphous ice leads to the formation of Na+ ions and to pronounced changes in the observed ultrafast dynamics compared to pure amorphous ice. We identify a Na+-induced species of excess electrons which exhibits a much longer lifetime compared to excess electrons in pure D2O ice and approximate the decay of the Na-induced contribution by two decay times τ2 = 880 fs and τ3 = 9.6 ps. In addition, a faster energetic stabilization of the excited electrons with a rate of Σ = 0.73 eV/ps is observed. The population of these electrons depends nonlinearly on the sodium coverage. We attribute the Na-induced contribution to a transient electron/ion/water complex which is located at the ice/vacuum interface. This interpretation is...

To investigate factors influencing nucleation of air clathrate hydrates in polar ice sheets, we have performed high-resolution mapping of the distributions of soluble impurities, air bubbles and air- hydrate crystals versus depth in the Dome Fuji Antarctic ice. Significant correlation observed between the concentrations of air inclusions and impurities in ice along with frequent occurrence of impurities inside hydrate crystals suggest that micro-inclusions promote hydrate nucleation in the ice matrix. Our observations also show that the diffusive macroscopic-scale redistribution of air constituents in ice in the bubble-hydrate transition zone is controlled by the original sedimentary layering of soluble impurities acting as nucleation helpers. The results of this study are important for the correct interpretation of high-resolution gas analyses of ice cores and for better understanding the global bubble-to-hydrate transformation process in polar ice sheets.

The state of the surface of amorphous ice with a specific surface area of about 160 m2/g obtained by the condensation of water vapor at 77 K is studied by IR spectroscopy. As the temperature increases to 130–160 K, absorption bands of surface hydroxyl groups vanish, whereas changes in bands characteristic of hydroxyl groups in the bulk of ice are indicative of a phase transition of ice from amorphous to the polycrystalline structure. The surface sites of amorphous ice are characterized with low-temperature adsorption of carbon monoxide. It is shown that there are two types of CO adsorption sites, free hydroxyl groups and oxygen atoms of surface coordinately unsaturated water molecules. Upon adsorption of nitrogen, methane, and carbon monoxide, in addition to the perturbation of surface OH groups, reversible changes in the spectrum are observed in the region of vibrations of bulk hydroxyls, which indicate that the strength of hydrogen bonds between water molecules in the surface layer of icy particles increases approaching the strength of these bonds in the crystal and that the ice surface becomes less amorphous. These results indicate that the properties of the ice surface layer substantially depend on the presence of adsorbed molecules.

We studied electrostatic charging on amorphous ice films induced by the impact of 100 keV Ar+ ions at 45° incidence. We derived the positive surface electrostatic potential from the kinetic energy of sputtered molecular ions. Measurements were performed as a function of film thickness, ion flux and accumulated fluence. The main results are (a) films charge up to a saturation value, following an exponential time dependence. (b) The time constant for charging is approximately proportional to the reciprocal of the ion flux. (c) The maximum surface voltage depends on film thickness and ion flux. (d) Charging does not occur for films thinner than the maximum range of projectile. (e) Dielectric breakdown is observed for surface potentials above ∼100 V. We explain the measurements with a model in which charges can drift into the substrate or be trapped temporarily near the ionization range of the projectiles. A charge can be released from the trap by the electric field produced by a nearby charge injected by subsequent projectiles.

Atmospheric conditions for growth of ice crystals (temperature and ice supersaturation) are often not well constrained and it is necessary to simulate such conditions in the laboratory to investigate such growth under well controlled conditions over many hours. The growth of ice crystals from the vapour in both prism and basal planes was observed at temperatures of -60 C and -70 C under ice supersaturation up to 100% (200% relative humidity) at pressures derived from the standard atmosphere in a static diffusion chamber. Crystals grew outward from a vertical glass filament, thickening in the basal plane by addition of macroscopic layers greater than 2 microns, leading to growth in the prism plane by passing of successive layers conveniently viewed by time lapse video.

At the Desert Research Institute, Reno, NV, USA, we investigated atmospheric ice crystal initiation, growth and interaction. We developed a mechanism of ice crystal growth in mixed clouds that is consistent with basic chemistry and physics, observations by others, and numerical studies of ice crystal growth from the vapor phase. The mechanism may provide insight into ice crystal morphology and charge separations in ice crystals growing in mixed clouds.

We analyze the heat capacity CP for low and high-density amorphous ice below the transition temperature (TC ≈ 140 K ) using a power-law formula. The renormalized critical exponent αR is extracted from the observed CP data, which describes similar critical behavior for both low and high-density amorphous ice below TC. Our analysis can also describe a glass transition in the low-density amorphous ice which is made from the high-density amorphous ice at 124 K, as observed experimentally.

The Cp calculation value (♦) of unfreezable bound water in PVME/water mixtures at low temperature. ◊: the experimental Cp of glassy water;21 □: the Cp of cubic ice.30

Our work was inspired by the recent brightening of Comet 17P/Holmes. The recently observed increase in brightness of this comet was correlated with emission of dust, probably larger in mass than the dust mantle of the nucleus. We analyzed the hypothesis that the comet can eject a large mass of dust due to non-uniform crystallization of amorphous water ice. For this purpose, we simulated the evolution of a model nucleus on the orbit of Comet 17P/Holmes. The nucleus is composed of water ice and dust and has the shape of an elongated ellipsoid. The simulations include crystallization of amorphous ice in the nucleus, changes in the dust mantle thickness, and changes in the nucleus orientation in space. Our computations indicate that: (i) ejection of the dust cover triggers crystallization of ice independently on the material properties of the nucleus; (ii) moderate changes in the nucleus orientation (∼50°) may result in an acceleration of the crystallization of ice in the northern hemisphere, while a rather large change in the orientation (∼120°) is needed to cause a significant jump of the crystallization front in the southern hemisphere, where the emission of dust during the recent brightening was strongest. We investigated the possible reason for an explosion and we have found that the crystallization of the water ice itself is probably not sufficient.

We study radiation-induced amorphization of crystalline ice, analyzing the results of three decades of experiments with a variety of projectiles, irradiation energy, and ice temperature, finding a similar trend of increasing resistance of amorphization with temperature and inconsistencies in results from different laboratories. We discuss the temperature dependence of amorphization in terms of the ‘thermal spike’ model. We then discuss the common use of the 1.65 μm infrared absorption band of water as a measure of degree of crystallinity, an increasingly common procedure to analyze remote sensing data of astronomical icy bodies. The discussion is based on new, high quality near-infrared reflectance absorption spectra measured between 1.4 and 2.2 μm for amorphous and crystalline ices irradiated with 225 keV protons at 80 K. We found that, after irradiation with 10 15 protons cm −2 , crystalline ice films thinner than the ion range become fully amorphous, and that the infrared absorption spectra show no significant changes upon further irradiation. The complete amorphization suggests that crystalline ice observed in the outer Solar System, including trans-neptunian objects, may results from heat from internal sources or from the impact of icy meteorites or comets.

We measured the neutron powder diffraction of 0.013 M KOD-doped D 2 O ice to investigate the formation process of ice XI, a hydrogen-ordered phase of ice Ih. The doped ice Ih transformed to ice XI after annealing at 57 and subsequently at 68 K. The mass fraction of ice XI to that of the doped ice ( f ) was estimated using Rietveld analysis for each sample. The f value of the doped ice, which had once experienced being ice XI ( f = 0.23), was larger than that of the doped ice, which had never experienced being ice XI ( f = 0.14). Results indicate that small hydrogen-ordered domains remained in the ice Ih, which had once transformed to ice XI, and accelerated the phase transition from ice Ih to ice XI. Results further suggest that large amounts of ice on icy bodies in our solar system can transform to ice XI, which might be detectable using infrared telescopes or planetary exploration in the near future.

We present the first clearly resolved observations of surfaces of growing and ablating hexagonal ice crystals using variable-pressure scanning electron microscopy. The ice surface develops trans-prismatic strands, separated from one another by distances of 5–10 μm. The strands are present at a wide range of supersaturations, but are most pronounced at temperatures near the frost point. Pyramidal facets consistent with Miller-Bravais indices of 1011, and possibly also 2021, are associated with ice growth under these conditions. A molecular-dynamics model of a free-standing ice Ih nanocolumn containing 8400 water molecules does not develop trans-prismatic strands, suggesting these features originate at larger spatial or temporal scales. The possible relevance of these surface features to cirrus ice is discussed.

Heterogeneous ice nucleation on solid ammonium sulfate and glutaric acid particles was studied using optical microscopy and Raman spectroscopy. Optical microscopy was used to detect selective nucleation events as water vapor was slowly introduced into an environmental sample cell. Particles that nucleated ice were dried via sublimation and examined in detail using Raman spectroscopy. Depositional ice nucleation is highly selective and occurred preferentially on just a few ammonium sulfate and glutaric acid particles in each sample. For freezing temperatures between 214 K and 235 K an average ice saturation ratio of S = 1.10±0.07 for solid ammonium sulfate was observed. Over the same temperature range, S values observed for ice nucleation on glutaric acid particles increased from 1.2 at 235 K to 1.6 at 218 K. Experiments with externally mixed particles further show that ammonium sulfate is a more potent ice nucleus than glutaric acid. Our results suggest that heterogeneous nucleation on ammonium sulfate may be an important pathway for atmospheric ice nucleation and cirrus cloud formation when solid ammonium sulfate aerosol particles are available for ice formation. This pathway for ice formation may be particularly significant near the tropical tropopause region where sulfates are abundant and other species known to be good ice nuclei are depleted.

Inelastic incoherent neutron scattering was used to study the phase transition process of high-density amorphous ice to low-density amorphous ice by annealing technique and the results show that the transformation occurs between 136 K and 144 K. From the comparison of high-density amorphous ice with low-density amorphous ice and ice Ih it is found that the internal interactions (covalent bond O-H and three-body interaction H-O-H) and their distances in high-density amorphous ice are strengthened and shortened, respectively, as nearest O-O distances are stretched longer from 2.75 A to 2.80 A (hydrogen bond length from 1.75 A to 1.82 A). Molecular dynamics simulation has been carried out for this phase transition procedure and TIP4P and rigid molecular model are adopted. High-density amorphous ice to low-density amorphous ice phase transition happens at about 130 K, which is good agreement with experimental result. Molar volume swells about 2.5% (density declines about 2.5%) during this phase transition. Low-density amorphous ice begins to melt at 230 K with its molar volume contracts back, which shows that low-density amorphous ice is amorphous ice and high-density amorphous ice is high-pressure water.

The smoothness and perceived quality of an ice cream depends in large part on the small size of ice crystals in the product. Understanding the mechanisms responsible for producing the disc-shaped crystals found in ice cream will greatly aid manufacturers in predicting how processing and formulation changes will affect their product. Because ice cream mix is opaque, it has not yet been possible to observe ice crystallization in ice cream in situ. Studies to date, therefore, have used analogues or have related observed effects to a hypothesized mechanism. Still, some elements of the crystallization mechanism are well accepted. Because of the large supercooling at the freezer wall, ice nucleates there before being swept into the bulk of the freezer. In the bulk, heat and mass transfer cause some crystals to melt and others to grow. By the time the ice cream reaches the freezer exit, the ice crystals have become small, rounded discs.

Polar stratospheric clouds (PSCs) are extremely efficient at catalysing the transformation of photostable chlorine reservoirs into photolabile species, which are actively involved in springtime ozone-depletion events. Why PSCs are such efficient catalysts, however, is not well understood. Here, we investigate the freezing behaviour of ternary HNO₃-H₂SO₄-H₂O droplets of micrometric size, which form type II PSC ice particles. We show that on freezing, a phase separation into pure ice and a residual solution coating occurs; this coating does not freeze but transforms into glass below ∼150 K. We find that the coating, which is thicker around young ice crystals, can still be approximately 30 nm around older ice crystals of diameter about 10 µm. These results affect our understanding of PSC microphysics and chemistry and suggest that chlorine-activation reactions are better studied on supercooled HNO₃-H₂SO₄-H₂O solutions rather than on a pure ice surface.

The complex behavior of water and the unusual properties of ferroelectric ice XI continue to attract much interest. Whether ice in the space exists as ice XI, is an important question, because long range electrostatic forces caused by the ferroelectricity might be an important factor for planet formation. From neutron diffraction experiments, we found the temperature and pressure conditions for the transformation of the largest fraction of ice into ferroelectric ice. It suggests that myriad big icy-bodies, which exist as dwarf planets and Kuiper Belt Object, consist of thick ferroelectric-ice surface. Furthermore, we report spectral and vibrational properties of ferroelectric ice investigated by inelastic neutron scattering and infrared absorption measurements. Because the spectral properties of ferroelectric ice are clearly different from those of ordinary ice, the distinct ferroelectric ice in the universe is detectable using infrared telescopes and planetary exploration.

This is a progress report on elucidating the behaviour of liquids,\ud in particular water, in confined geometry on the nano- to mesoscale,\ud and at interfaces. There are important measurements still\ud to make, conclusions still to be drawn, and above all leaps of\ud understanding still to be made. However, a number of important\ud features in the behaviour of these systems have recently become\ud clearer.\ud Nano-structuring of liquids and their crystals changes their\ud Gibbs free energy, and hence their dynamics. This may most readily\ud be probed by monitoring the alteration of phase changes as a\ud function of temperature, together with changes in other parameters,\ud particularly the confinement diameter. Such studies may be\ud performed by monitoring the change in the pressure (at constant\ud temperature) of the liquid in its own vapour (Kelvin equation), or\ud by monitoring the change in the freezing/melting temperature\ud (at constant pressure) of a crystal in its own liquid (Gibbs–Thomson\ud equation).\ud In the latter case the melting and freezing temperatures of liquids\ud are modified by the changes in the volumetric Gibbs free energy\ud due to nanostructuring; this is related to the surface energy of\ud the curved interface between the crystal and its own liquid. This is\ud thus dependent on the geometry of the interface between the crystal\ud and its liquid. There is still discussion on this point as to the exact\ud geometric constants and functional forms that are applicable\ud for different confining geometries. Experimental evidence is presented\ud for the cases of cylindrical pores (SBA-15), and for pores\ud that on average are spherical (sol–gel). However, reconciling this\ud comparative data with melting/freezing temperatures in each of\ud these systems still pose a number of questions.\ud It is well known that bulk brittle ice has a hexagonal structure,\ud while brittle ice that forms in pores may be cubic in structure [1,2],\ud Figs. 10 and 11. Adjacent surfaces appear to further alter the\ud dynamics and structure of confined liquids and their crystals, leading\ud in the case of a water/ice system to a state of enhanced rotational\ud motion (plastic ice) just below the confined freezing/\ud melting transitions. This plastic ice layer appears to form at both\ud the ice–silica interface and the ice–vapour surface, and reversibly\ud transforms to brittle ice at lower temperatures. There is good evidence\ud to suggest that the plastic ice at a silica interface transforms\ud to cubic ice, while the plastic ice at vapour surfaces transforms to\ud hexagonal ice. That this plastic ice may correspond to a layer at the\ud crystal surface is suggested by the presence of only amorphous ice\ud in confined systems with small dimensions (30 nm) contain predominately hexagonal\ud ice. It is conjectured that this layer of plastic ice at vapour\ud surfaces may be present at the myriad of such interfaces in macroscopic\ud systems, such as snow-packs, glaciers and icebergs, and may\ud be an explanation for the need for plastic terms in the macroscopic\ud dynamical models of these systems [3].\ud These results also point the way forward for a wide-range of\ud cryoporometric metrology studies of systems that are ‘difficult’\ud for NMR, such as high iron content clays and rocks, as well as aged\ud concrete. Results are presented for cryoporometric measurements\ud on meteorite samples with a significant metallic content, exhibiting\ud T2 relaxation times down to 2.5 us.

Ice chromatography, in which water-ice particles are employed as a chromatographic stationary phase, has proven an efficient technique for probing the solution/ice interface. The preparation of fine ice particles has allowed us to not only obtain higher-resolution separation but also investigate the molecular processes occurring on the ice surface in more detail. Chromatographic investigations have revealed that two or more hydrogen bonds are simultaneously formed between a solute and the dangling bonds on the ice surface when the solute gives measurable retention. Several compounds, including estrogens, amino acids, and acyclic polyethers, have been successfully separated by ice chromatography with a hexane-based mobile phase. In addition, this method effectively probes the surface melting of the ice stationary phase and the liquid phase that coexists with water ice at thermodynamic equilibrium. The thickness of the surface liquid layer and the size of the liquid phase that grows inside an ice particle have been evaluated. The perspectives of this method are also discussed.

The changes in situ in Raman spectra of ice in aqueous KOH solution as a function of pressure at liquid nitrogen temperature (77 K) have been examined. The possibility that the ice in aqueous KOH directly transforms to the low-temperature ice IX phase at around 1 GPa, not via high-density amorphous ice, is shown. Also, it is reported that the results show differences strongly depend on the salts dissolved in the aqueous solutions.

According to observations, a large relative humidity with respect to ice, RH(i)100%, often persists outside and inside upper tropospheric cirrus ice clouds. The persistence of the large in-cloud RH(i) means that H(2)O is slowly deposited onto cloud ice crystals. This unusual physical situation is similar to one in which a released body would slowly fall owing to gravitation. Here we present a physical mechanism which can be responsible for the persistence of large in-cloud RH(i). We find that clear-sky RH(i) up to 176% can be built up prior to the formation of ice cirrus by the homogeneous freezing of aqueous droplets containing H(2)SO(4) and HNO(3). As the droplets are cooled, a phase separation, which occurs during freezing, leads to the formation of a residual solution coating around the ice crystals formed. The coating can serve as a shield, slowing the rate of ice growth by approximately 10(3) in comparison with uncoated ice, and this can be a reason for the persistence of the large in-cloud RH(i).

The structural transformation of different high-density amorphous (HDA) ice modifications into the low-density amorphous (LDA) ice is studied by small-angle neutron scattering (SANS) techniques. All experiments have been performed at stationary conditions allowing to collect detailed information not only on the SANS formfactor but also on its time evolution and, hence, the kinetics governing the transformation process. A parametrization of the SANS formfactor by a superposition of the Debye-Bueche formfactor, characterizing a non-particulate two phase mixture, and a Porod-limit scattering formfactor is carried out successfully. The Porod-limit scattering indicates the presence of sharp interfaces and surfaces present in the sample material. Interpreting this signal as due to a grainy consistency of the amorphous samples grain sizes of the order of at least some micrometers can be approximated. The Debye-Bueche ansatz accounts for the formation of a transient pronounced signal on mesoscopic length scales. Its analysis results in an average domain size of 12–16 Å characterizing a hypothetical two phase mixture in its state of strongest intermixture, i.e., strongest heterogeneity. Interpretation of the Debye-Bueche formfactor by the Porod invariant results in a sample contrast that is by a factor of about 4 smaller than a hypothetical first-order transition between any modification of HDA and LDA. This statement is valid for an unstrained two-phase system separated by sharp interfaces. A detailed discussion is given which tries to set the present results into a more realistic context.

The crystalline state of water ice in the Solar System depends on the temperature history of the ice and the influence of energetic particles to which it has been exposed. We measured the infrared absorption spectra of amorphous and crystalline water ice in the 10-50 K and 10-140 K temperature range, respectively, and conducted a systematic experimental study to investigate the amorphization of crystalline water ice via ionizing radiation irradiation at doses of up to 160 \pm 30 eV per molecule. We found that crystalline water ice can be converted only partially to amorphous ice by electron irradiation. The experiments showed that a fraction of the 1.65 \mum band, which is characteristic for crystalline water ice, survived the irradiation, to a degree that strongly depends on the temperature. Quantitative kinetic fits of the temporal evolution of the 1.65 \mum band clearly demonstrate that there is a balance between thermal recrystallization and irradiation-induced amorphization, with thermal recrystallizaton dominant at higher temperatures. Our experiments show the amorphization at 40K was incomplete, in contradiction to Mastrapa and Brown's conclusion (Icarus 2006, 183, 207.). At 50 K, the recrystallization due to thermal effects is strong, and most of the crystalline ice survived. Temperatures of most icy objects in the Solar System, including Jovian satellites, Saturnian satellites (including Titan), and Kuiper Belt Objects, are equal to or above 50 K; this explains why water ice detected on those objects is mostly crystalline., 23 pages, 5 figures

Formation of H2O molecules through the codeposition of oxygen molecules and hydrogen atoms is examined in situ using IR spectroscopy at 10-40 K under various O2 and H fluxes. It is found that H2O and H2O2 are continuously formed by reaction, even at 40 K. The H2O ice formed is amorphous, but has a compact (not microporous) structure compared to vapor-deposited amorphous H2O ice, because dangling OH bonds are not observed in the IR spectrum. This is consistent with astronomical observations in molecular clouds and theoretical predictions, which suggest that hydrogenation of O2 is one of the potential routes for reproducing these IR spectral characteristics. The composition of the ice formed by codeposition varies with the O2/H ratio and temperature. Although no data are available at present for the H2O/H2O2 ratio of ice in molecular clouds, this study suggests that hydrogenation of O2 has a potential to yield a H2O/H2O2 ratio of 5 or more in molecular clouds.

We present observational data for two long-period and three dynamically new comets observed at heliocentric distances between 5.8 to 14.0 AU. All of the comets exhibited activity beyond the distance at which water ice sublimation can be significant. We have conducted experiments on gas-laden amorphous ice samples and show that considerable gas emission occurs when the ice is heated below the temperature of the amorphous–crystalline ice phase transition ( T ∼ 137 K ). We propose that annealing of amorphous water ice is the driver of activity in comets as they first enter the inner Solar System. Experimental data show that large grains can be ejected at low velocity during annealing and that the rate of brightening of the comet should decrease as the heliocentric distance decreases. These results are consistent with both historical observations of distant comet activity and with the data presented here. If observations of the onset of activity in a dynamically new comet are ever made, the distance at which this occurs would be a sensitive indicator of the temperature at which the comet had formed or represents the maximum temperature that it has experienced. New surveys such as Pan STARRS, may be able to detect these comets while they are still inactive.

This article mainly presents applications of previously derived formulas by the author to experimental systems whereby the Markovian and non-Markovian multimode Brownian oscillator (MBO) model and their consequent dynamics are explored. These applications include computing the zero-phonon line (ZPL) widths of aluminum phthalocyanine tetrasulphonate (APT) in glassy films of water and ethanol, which are compared to those of the Ohmic MBO model-calculated ZPL widths at different temperatures. The analytical forms of the ZPL width and Franck–Condon factors (FCF) derived from the high-temperature limit underdamped MBO model absorption line shape (Toutounji, Chem Phys, 2003, 293, 311) are recovered from the finite-temperature MBO model, which includes Matsubara terms (Toutounji and Small, J Chem Phys, 2002, 117, 3848). As the applicability of the Ohmic MBO model at low temperatures is questionable, the corresponding low-temperature (T) Markovian dynamics is discussed. A formula for the Ohmic MBO model ZPL FCF at T = 0 is presented. It is established that this formula reduces to e−S, S is Huang–Rhys factor, at T = 0, which further ratifies our previous conclusion (Toutounji and Small, J Chem Phys, 2002, 117, 3848) that the bath modes are completely thwarted from contributing to the ZPL profile at this T. Hayes–Small theory of linear absorption and hole-burning line shapes is discussed and compared to that of the MBO model and other line shapes. Overdamped Ohmic MBO model is briefly discussed. Illustrative calculations are presented. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009

The Centaurs are recent escapees from the Kuiper belt that are destined either to meet fiery oblivion in the hot inner regions of the Solar system or to be ejected to the interstellar medium by gravitational scattering from the giant planets. Dynamically evolved Centaurs, when captured by Jupiter and close enough to the Sun for near-surface water ice to sublimate, are conventionally labeled as "short-period" (specifically, Jupiter-family) comets. Remarkably, some Centaurs show comet-like activity even when far beyond the orbit of Jupiter, suggesting mass-loss driven by a process other than the sublimation of water ice. We observed a sample of 23 Centaurs and found nine to be active, with mass-loss rates measured from several kg/s to several tonnes/s. Considered as a group, we find that the "active Centaurs" in our sample have perihelia smaller than the inactive Centaurs (median 5.9 AU vs. 8.7 AU), and smaller than the median perihelion distance computed for all known Centaurs (12.4 AU). This suggests that their activity is thermally driven. There are several possibilities for the origin of the mass-loss from the active Centaurs. We consider the possibility that activity in the Centaurs is triggered by the conversion of amorphous ice into the crystalline form accompanied by the release of trapped gases, including carbon monoxide. By imposing the condition that crystallization should occur when the crystallization time is shorter than the orbital period we find a qualitative match to the perihelion distribution of the active Centaurs and conclude that the data are consistent with the hypothesis that the Centaurs contain amorphous ice., Comment: 52pages, 15 figures, accepted by AJ February 24 2009

A mathematical model of electrical processes that take place upon the evaporation of water and sublimation of ice, as well as the condensation growth of water and ice phases from vapor, is proposed. The transfer of the main charge carriers, such as (i) protons and hydroxide ions (in ice, water, and vapor and (ii) orientational defects (in ice and water) is taken into account. Upon the evaporation of water and the sublimation of ice, the first carriers are accumulated before the phase front and cause positive charges in the surface of the water and ice, while the second carriers are depleted (their concentration becomes lower than the thermodynamic value) and impart a negative charge to water and ice. The contribution of protons and hydroxide ions dominates at a low rate of evaporation. In the condensation of vapor and relevant growth of water and ice phases, the polarity of surface charge is opposite to that observed upon evaporation. The values of interfacial current and signs of phase charges upon sublimation, evaporation, and condensation that are predicted in the model comply with experimental data.

It is still unclear whether hyperquenched water (i.e., amorphous glassy water) heated to about 140-150 K remains glassy until it crystallizes near 154 K or whether instead it turns into a supercooled and very viscous liquid. It has been proposed that the glass transition temperature (T(g)) for water is 165 K and not, as previously thought, 136 K [V. Velikov et al., Science, 294, 2335 (2001)]. Support for both interpretations exists in the literature, since the T(g) of water is difficult to measure due to the formation of metastable cubic ice (I(c)) near 154 K. To address the nature of water in the 110-160 K temperature range, a confocal microscopy approach is used to study whether single-probe molecules (i.e., Rhodamine 700, Rh-700) embedded in hyperquenched glassy water (HGW) rotate in the temperature range of 110-160 K. If T(g) is 136 K and the liquid above this temperature is fragile (or strong with the fragility index m > 7), then rotation of the Rh-700 molecules should be observed several degrees above T(g). It is shown that no anticorrelated fluorescence intensity changes of single molecules in HGW (when excited at orthogonal polarizations) were observed up to temperatures of 160 K, although such changes were detected in control experiments performed for hyperquenched glassy ethanol (fragile liquid) at 99 K, that is, at T(g) + 2 K. The viscosity at which single Rh-700 molecules rotate in ethanol at 99 K is estimated to be about 10(12) poise. Since single-molecule spectroscopy did not reveal any rotation of probe molecules in HGW above 136 K, we conclude that water above 136 K is most likely a solid (i.e., glass), supporting the assignment that water remains glassy until it crystallizes near T = 154 K. It cannot be excluded, of course, that the value of m for water is smaller than 7 (i.e., water above 136 K could be an extremely strong liquid), but this possibility is considered unlikely as this would make water the strongest liquid ever known.

We present the hypothesis of homogeneous nucleation of ice nano-particles in the polar summer mesosphere. The nucleation of condensed phase is traced back to the first step on the formation pathway, which is assumed to be the transition of water vapor to amorphous cluster. Amorphous clusters then freeze into water ice, likely metastable cubic ice, when they reach the critical size. The estimates based on the equilibrium thermodynamics give the critical size (radius) of amorphous water clusters as about 1.0 nm. The same estimates for the final transition step, that is the transformation of cubic to hexagonal ice, give the critical size of about 15 nm at typical upper mesospheric conditions during the polar summer (temperature T=150 K, water vapor density ρvapor=109 cm−3).

We examined the effect of pore geometry on the stability of cubic ice in mesopores by measuring the change of the X-ray diffraction pattern for ice confined in cylindrical, interconnected cylindrical, interconnected spherical, and interconnected irregular pores of silica during a heating process. The results obtained clearly indicated that the stability of cubic ice in the mesopores depends on the pore geometry. Cubic ice confined to the interconnected spherical cavities of KIT-5 is metastable with respect to hexagonal ice, similar to bulk cubic ice. On the other hand, cubic ice confined to the cylindrical and interconnected cylindrical pores of SBA-15 and KIT-6 is stable up to the melting point of the ice, in accord with previous studies.

The surface of ice and snow is slippery. This slipperiness property of ice surface has been usually explained by a lubricating layer of water film, which exists in the surface. Ice crystal has a melting layer on the surface even at low temperatures below the bulk melting point. The properties of ice surface have attracted scientific interests for more than a century, ever since 1859 when Faraday predicted the existence of a melting layer on ice surface. This paper reviews the dynamics of ice surface and the effects of the dynamics on the formation process of the melting layer in ice surface.

(Received 4 June 2009; Accepted 7 June 2009; Published 11 June 2009)We report first results about the ability of low density amorphous ice nanolayers to behave as a “matrix” andtrap monomeric neutral glycine molecules at 125 K, a temperature much greater than the commonly used liquidHe temperature region. FTIR-RAS spectra of those monomeric neutral glycine molecules adsorbed on low denseamorphous ice were obtained for the first time and indicate that glycine adsorbs molecularly with the carboxylicgroup and the nitrogen atom hydrogen-bonded to the ice surface. [DOI: 10.1380/ejssnt.2009.693]

Heterogeneous depositional nucleation of ice particles may dominate in atmospheric regions with very low temperatures, where low vapor pressures and insoluble nuclei would be expected. However, depositional ice nucleation has not been studied extensively at temperatures below 200 K and not at all below 170 K. Here, we show results of a study of heterogeneous depositional nucleation of ice on a solid silicon substrate at temperatures from 150 to 180 K. The results presented herein demonstrate an unexpected temperature dependence in which very high critical supersaturations are required to nucleate ice at T ≤ 180 K. The vapor pressures necessary for nucleation below 175 K are greater than the vapor saturation for supercooled liquid water. The temperature dependence observed is not predicted by classical heterogeneous nucleation theory, when assuming a temperature-independent contact parameter, m. Here, we use our new measurements in combination with previously published data to derive a temperature-dependen...