Crystalline Ice Research Articles

Distinguishing Amorphous and Crystalline Ice by Ultralow Energy Collisions of Reactive Ions

Ion scattering using ultralow energy projectiles is considered to be a unique method to probe the nature of molecular surfaces because of its capacity to probe the very top, atomically thin layers. Here, we examine one of the most studied molecular solids, water-ice, using this technique. When ice surface undergoes the amorphous to crystalline transition, an ultralow energy reactive projectile identifies the change through the reaction product formed. It is shown that ultralow energy (2, 3, 4, 5, 6, and 7 eV) CH2+ (or CD2+) collision on amorphous D2O (or H2O) ice makes CHD+, while crystalline ice does not. The projectile undergoes H/D exchange with the dangling −OD (−OH) bond present on amorphous ice surfaces. It is also shown that H/D exchange product disappears when amorphous ice is annealed to the crystalline phase. The H/D exchange reaction is shown to be sensitive only to the surface layers of ice as it disappears when the surface is covered with long chain alcohols like 1-pentanol as the ice surface...

Defect pair separation as the controlling step in homogeneous ice melting

On being heated, ice melts into liquid water. Although in practice this process tends to be heterogeneous, it can occur homogeneously inside bulk ice. The thermally induced homogeneous melting of solids is fairly well understood, and involves the formation and growth of melting nuclei. But in the case of water, resilient hydrogen bonds render ice melting more complex. We know that the first defects appearing during homogeneous ice melting are pairs of five- and seven-membered rings, which appear and disappear repeatedly and randomly in space and time in the crystalline ice structure. However, the accumulation of these defects to form an aggregate is nearly additive in energy, and results in a steep free energy increase that suppresses further growth. Here we report molecular dynamics simulations of homogeneous ice melting that identify as a crucial first step not the formation but rather the spatial separation of a defect pair. We find that once it is separated, the defect pair--either an interstitial (I) and a vacancy (V) defect pair (a Frenkel pair), or an L and a D defect pair (a Bjerrum pair)--is entropically stabilized, or 'entangled'. In this state, defects with threefold hydrogen-bond coordination persist and grow, and thereby prepare the system for subsequent rapid melting.

Low temperature phase properties of water confined in mesoporous silica MCM-41: Thermodynamic and neutron scattering study

The phase properties of water confined in mesoporous silica MCM-41 were investigated over a temperature range of 100-298 K as a function of pore size by specific heat capacity and inelastic neutron scattering (INS) measurements. The water content of the samples was carefully controlled to ensure the capillary filled state and no overloading of water. The values of heat capacity of the pore water are higher than those of bulk ice and liquid water over the whole temperature range measured. The contribution of water in the inner part of pores (abbreviated as the internal water) was elucidated by using the heat capacity data of monolayer water measured. The entropy of the internal water was then estimated from integration of the heat capacity of the internal water. The entropy values of the internal water increase by confinement in the pores of MCM-41 in both liquid and frozen regions, indicating an increase in the deformation of the structure and∕or a change in the dynamics in both regions. The INS spectra show the density of states for the librational motion of water frozen at 50 K, suggesting that the confined water is similar to amorphous ice rather than to crystalline ice. When the sample is warmed to melt, the band edge of the librational motion for water frozen in large pores (diameter of 3.6 nm) shifts to a lower energy side, indicating the weakening of intermolecular hydrogen bonds. For water in small pores (2.1 nm), on the contrary, the librational band shifts slightly to a higher energy side, suggesting the low density liquid to high density liquid transition (L-L transition) at 225-250 K. A plausible mechanism of the L-L transition of water in confinement is proposed in terms of incomplete growth of homogeneous nucleation of ice due to an interfacial free energy effect to inhibit crystallization of water confined in small pores.

Ionization of Nitric Acid on Crystalline Ice: The Role of Defects and Collective Proton Movement.

Ionization of nitric acid (HNO3) on a model ice surface is studied using ab initio molecular dynamics at temperatures of 200 and 40 K with a surface slab model that consists of the ideal ice basal plane with locally optimized and annealed defects. Pico- and subpicosecond ionization of nitric acid can be achieved in the defect sites. Key features of the rapid ionization are (a) the efficient solvation of the polyatomic nitrate anion, by stealing hydrogen bonds from the weakened hydrogen bonds at defect sites, (b) formation of contact ion pairs to stable "presolvated" molecular species that are present at the defects,

Activity of Comet 29P/Schwassmann–Wachmann 1

Comet 29P/Schwassmann–Wachmann 1 is a continually active object moving along nearly circular orbit at a large heliocentric distance ∼6AU. The comet is famous for its repeated outbursts. We look for structure and composition of the nucleus that leads to the observed frequent outbursts. We performed series of numerical simulations dealing with evolution of the nucleus, including changes of the structure and of the CO gas pressure. In our model the porous nucleus has layered structure. Outermost layer is composed of grains with nonvolatile cores mantled by crystalline water ice. Deeper the grains have three components: non-volatile cores, amorphous water ice and, the carbon monoxide ice. The simulations include crystallization of amorphous ice in the nucleus, sublimation of the CO ice and local explosions. We have found, that for an equatorial location the explosions can be expected only in special case, when the nucleus is fine grained, fluffy and rich in CO. In polar regions explosions are possible for almost any composition and structure of the nucleus. Explosions can be either single, or multiple.

ANOMALOUS CO2ICE TOWARD HOPS-68: A TRACER OF PROTOSTELLAR FEEDBACK

We report the detection of a unique CO2 ice band toward the deeply embedded, low-mass protostar HOPS-68. Our spectrum, obtained with the Infrared Spectrograph onboard the Spitzer Space Telescope, reveals a 15.2 micron CO2 ice bending mode profile that cannot modeled with the same ice structure typically found toward other protostars. We develop a modified CO2 ice profile decomposition, including the addition of new high-quality laboratory spectra of pure, crystalline CO2 ice. Using this model, we find that 87-92% of the CO2 is sequestered as spherical, CO2-rich mantles, while typical interstellar ices show evidence of irregularly-shaped, hydrogen-rich mantles. We propose that (1) the nearly complete absence of unprocessed ices along the line-of-sight is due to the flattened envelope structure of HOPS-68, which lacks cold absorbing material in its outer envelope, and possesses an extreme concentration of material within its inner (10 AU) envelope region and (2) an energetic event led to the evaporation of inner envelope ices, followed by cooling and re-condensation, explaining the sequestration of spherical, CO2 ice mantles in a hydrogen-poor mixture. The mechanism responsible for the sublimation could be either a transient accretion event or shocks in the interaction region between the protostellar outflow and envelope. The proposed scenario is consistent with the rarity of the observed CO2 ice profile, the formation of nearly pure CO2 ice, and the production of spherical ice mantles. HOPS-68 may therefore provide a unique window into the protostellar feedback process, as outflows and heating shape the physical and chemical structure of protostellar envelopes and molecular clouds.

Glassy Character of DNA Hydration Water

The coherent excitations of DNA hydration water at 100 K have been investigated by neutron scattering spectroscopy to extract the excess signal of D(2)O-hydrated DNA with respect to dry DNA samples. A structural characterization of the sample, through the analysis of the static structure factor, has suggested that DNA hydration water is largely in an amorphous state up to high hydration degree, with only a small contribution coming from slightly deformed crystalline ice. To describe the inelastic spectra of DNA hydration water, we exploited a phenomenological model already applied in similar disordered systems, such as bulk water (Sacchetti et al. Phys. Rev. E2004, 69, 061203; Petrillo et al. Phys. Rev. E2000, 62, 3611-3618; Sette et al. Phys. Rev. Lett.1996, 77, 83-86) and protein hydration water (Orecchini et al. J. Am. Chem. Soc.2009, 131, 4664-4669). Over the low-energy range, the coherent dynamics of DNA hydration water is characterized by a branch at about 7.5 meV, a value slightly larger than that of bulk water. An additional mode in the energy range 20-35 meV is found, with a wavevector dependence seemingly connected with the structural features of amorphous ice. The ensemble of the results supports the glassy nature of DNA hydration water.

Limits of metastability in amorphous ices:2H-NMR relaxation

The high-frequency reorientation dynamics of O-(2)H bonds is investigated in various amorphous ices including eHDA (expanded high density amorphous ice), LDA-II (low density amorphous ice II) and HGW (hyperquenched glassy water) using (2)H-NMR spin-lattice relaxation as a local probe. Both low density forms, HGW and LDA-II, show similar spin-lattice relaxation but differ in the thermal stability with respect to the transition into crystalline cubic ice I(c). HGW already transforms slightly above 135 K whereas LDA-II crystallizes at 150 K. eHDA is distinguishable from other high density amorphous ices in its thermal stability and spin-lattice relaxation. Its relaxation times are much larger compared to those of VHDA (very high density amorphous ice) and uHDA (unrelaxed high density amorphous ice). eHDA does not show annealing effects, transforms sharply into LDA-II above 123 K and provides higher thermal stability as compared to other high density forms.

Topological characterization of crystalline ice structures from coordination sequences

Topological properties of crystalline ice structures are studied by considering ring statistics, coordination sequences, and topological density of different ice phases. The coordination sequences (number of sites at topological distance k from a reference site) have been obtained by direct enumeration until at least 40 coordination spheres for different ice polymorphs. This allows us to study the asymptotic behavior of the mean number of sites in the k-th shell, Mk, for high values of k: Mk~ak(2), a being a structure-dependent parameter. Small departures from a strict parabolic dependence have been studied by considering first and second differences of the series {Mk} for each structure. The parameter a ranges from 2.00 for ice VI to 4.27 for ice XII, and is used to define a topological density for these solid phases of water. Correlations between such topological density and the actual volume of ice phases are discussed. Ices Ih and Ic are found to depart from the general trend in this correlation due to the large void space in their structures.

Vibrational spectroscopic observation of ice dewetting on MgO(001)

The properties of the interfacial water monolayer on MgO(001) during growth of multilayer ice and, in particular, the dewetting of crystalline ice on MgO(001) are revealed by vibrational sum frequency generation and infrared reflection absorption spectroscopy.

PROBING DYNAMICAL PROCESSES IN THE PLANET-FORMING REGION WITH DUST MINERALOGY

We present Herschel Space Observatory PACS spectra of GQ Lup, a protoplanetary disk in the Lupus star-forming region. Through SED fitting from 0.3{\mu}m to 1.3mm, we construct a self-consistent model of this system's temperature and density structures, finding that although it is 3 Myr old, its dust has not settled to the midplane substantially. The disk has a radial gradient in both the silicate dust composition and grain size, with large amorphous grains in the upper layers of the inner disk and an enhancement of submicron, crystalline grains in the outer disk. We detect an excess of emission in the Herschel PACS B2A band near 63{\mu}m and model it with a combination of {\sim}15 to 70{\mu}m crystalline water ice grains with a size distribution consistent with ice recondensation-enhanced grain growth and a mass fraction half of that of our solar system. The combination of crystalline water ice and silicates in the outer disk is suggestive of disk-wide heating events or planetesimal collisions. If confirmed, this would be the first detection of water ice by Herschel.

Regolith grain sizes of Saturn’s rings inferred from Cassini–CIRS far-infrared spectra

We analyze far-infrared (10–650cm−1) emissivity spectra of Saturn’s main rings obtained by the Cassini Composite Infrared Spectrometer (CIRS). In modeling of the spectra, the single scattering albedos of regolith grains are calculated using the Mie theory, diffraction is removed with the delta-Eddington approximation, and the hemispherical emissivities of macroscopic free-floating ring particles are calculated using the Hapke’s isotropic scattering model. Only pure crystalline water ice is considered and the size distribution of regolith grains is estimated. We find that good fits are obtained if the size distribution is broad ranging from 1μm to 1–10cm with a power law index of ∼3. This means that the largest regolith grains are comparable to the smallest free-floating particles in size and that the power law indices for both free-floating particles and regolith grains are similar to each other. The apparent relative abundance of small grains increases with decreasing solar phase angle (or increasing mean temperature). This trend is particularly strong for the C ring and is probably caused by eclipse cooling in Saturn’s shadow, which relatively suppresses warming up of grains larger than the thermal skin depth (∼1mm) under subsequent solar illumination.

ChemInform Abstract: Prebiotic Chemistry in Eutectic Solutions at the Water—Ice Matrix

AbstractReview: 123 refs.

SIZE AND TEMPERATURE DEPENDENCE IN THE FAR-IR SPECTRA OF WATER ICE PARTICLES

Spectra of water-ice aerosol particles have been measured in the far-IR region using synchrotron radiation. The particles in the nanoscale size regime of 1-100 nm were formed by rapid collisional cooling at temperatures ranging from 4 to 190 K. The spectra show the characteristic bands centered near 44 μm (230 cm–1) and 62 μm (160 cm–1) associated with the intermolecular lattice modes of crystalline ice at all temperatures, in contrast to previous studies of thin films formed by vapor deposition where amorphous ice is generated below 140 K. The bands shift to higher wavenumber values as the temperature is reduced, consistent with the trend seen in earlier studies, but in our experiments the actual peak positions in the aerosol particle spectra are consistently higher by ca. 4 cm–1. This finding has implications for the potential use of these spectral features as a temperature probe. The particle sizes are small enough for their spectra to be free of scattering effects, and therefore provide a means to assess imaginary refractive index values obtained through Kramers-Kronig analyses of thin film spectra.

Growth of volcanic ash aggregates in the presence of liquid water and ice: an experimental approach

Key processes influencing the aggregation of volcanic ash and hydrometeors are examined with an experimental method employing vibratory pan aggregation. Mechanisms of aggregation in the presence of hail and ice pellets, liquid water (≤30 wt%), and mixed water phases are investigated at temperatures of 18 and −20 °C. The experimentally generated aggregates, examined in hand sample, impregnated thin sections, SEM imagery, and X-ray microtomography, closely match natural examples from phreatomagmatic phases of the 27 ka Oruanui and 2010 Eyjafjallajokull eruptions. Laser diffraction particle size analysis of parent ash and aggregates is also used to calculate the first experimentally derived aggregation coefficients that account for changing liquid water contents and subzero temperatures. These indicate that dry conditions ( 1). In contrast, liquid-saturated conditions (>15–20 wt% liquid) promote less size selective processes. Crystalline ice was also capable of preferentially selecting volcanic ash <31 μm under liquid-free conditions in a two-stage process of electrostatic attraction followed by ice sintering. However, this did not accumulate more than a monolayer of ash at the ice surface. These quantitative relationships may be used to predict the timescales and characteristics of aggregation, such as aggregate size spectra, densities, and constituent particle size characteristics, when the initial size distribution and water content of a volcanic cloud are known. The presence of an irregularly shaped, millimeter-scale vacuole at the center of natural aggregates was also replicated during interaction of ash and melting ice pellets, followed by sublimation. Fine-grained rims were formed by adding moist aggregates to a dry mixture of sub-31 μm ash, which adhered by electrostatic forces and sparse liquid bridges. From this, we infer that the fine-grained outer layers of natural aggregates reflect recycled exposure of moist aggregates to regions of volcanic clouds that are relatively dry and dominated by <31 μm ash.

Glycine phases formed from frozen aqueous solutions: Revisited

Glycine phases formed when aqueous solutions were frozen and subsequently heated under different conditions were studied by Raman scattering, x-ray diffraction, and differential scanning calorimetry (DSC) techniques. Crystallization of ice I(h) was observed in all the cases. On cooling at the rates of 0.5 K∕min and 5 K∕min, glassy glycine was formed as an intermediate phase which lived about 1 min or less only, and then transformed into β-polymorph of glycine. Quench cooling of glycine solutions (15% w∕w) in liquid nitrogen resulted in the formation of a mixture of crystalline water ice I(h) and a glassy glycine, which could be preserved at cryogenic temperatures (80 K) for an indefinitely long time. This mixture remained also quite stable for some time after heating above the cryogenic temperature. Subsequent heating under various conditions resulted in the transformation of the glycine glass into an unknown crystalline phase (glycine "X-phase") at 209-216 K, which at 218-226 K transformed into β-polymorph of glycine. The "X-phase" was characterized by Raman spectroscopy; it could be obtained in noticeable amounts using a special preparation technique and tentatively characterized by x-ray powder diffraction (P2, a = 6.648 Å, b = 25.867 Å, c = 5.610 Å, β = 113.12[ordinal indicator, masculine]); the formation of "X-phase" from the glycine glassy phase and its transformation into β-polymorph were followed by DSC. Raman scattering technique with its power for unambiguous identification of the crystalline and glassy polymorphs without limitation on the crystallite size helped us to follow the phase transformations during quenching, heating, and annealing. The experimental findings are considered in relation to the problem of control of glycine polymorphism on crystallization.

A cometary nucleus model taking into account all phase changes of water ice: amorphous, crystalline, and clathrate

Context. Current theories, models of cometary nuclei and of ice formation in the protoplanetary disk, and laboratory studies suggest that cometary materials could be formed of pure crystalline water ice, amorphous water ice, clathrate hydrate, or a mixture of these structures of water ice. However, current models of cometary nuclei consider only two forms of ice during the thermodynamic evolution of comets: amorphous and crystalline water ices. Aims. In this work, we have developed a model of cometary nucleus that takes into account all water ice structures and phase changes in order to predict the outgassing profile of volatile molecules that could be measured by the Rosetta mission and can be used to constrain the structural type of ice existing in the interior of the Comet 67P/Churyumov-Gerasimenko, the target comet of the Rosetta mission, and, hopefully, its initial composition.Methods. We added the physic of formation/dissociation of clathrate hydrates in addition to others physical processes that are taken into account in models without clathrate hydrates. All thermal changes, as well as the release and trapping of gas with water phase changes are taken into account.Results. This model describes heat transmission, latent heat exchanges, all water ices structures and transitions (amorphous-to-pure crystalline, amorphous-to-clathrate hydrates and pure crystalline-to-clathrate hydrates and vise versa), sublimation/recondensation of volatile molecules in the nucleus, gas diffusion, gas released and trapped by crystallization and clathrate formation/dissociation processes, as well as gas and dust release and mantle formation at the surface. Applying this model to the comet 67P/Churyumov-Gerasimenko, results show different outgassing profiles of volatiles molecules from the nucleus depending on the water ice structure, the distribution of volatile molecules between the “trapped” and “condensed” states in the nucleus and the thermal inertia of its porous matrix. Conclusions. Given these results, we pretend that this model is able to constrain the water ice structure and chemical composition in comets from outgassing profiles of volatile molecules, and especially those of the target comet of the Rosetta mission.

Comment on Yakovlev, S. &amp; Downing, K.H. (2011) Crystalline ice as a cryoprotectant: theoretical calculation of cooling speed in capillary tubes. J. Microsc. 243, 8–14.

Journal of MicroscopyVolume 246, Issue 3 p. 322-322 Comment on Yakovlev, S. & Downing, K.H. (2011) Crystalline ice as a cryoprotectant: theoretical calculation of cooling speed in capillary tubes. J. Microsc. 243, 8–14. First published: 14 May 2012 https://doi.org/10.1111/j.1365-2818.2012.03612.xCitations: 1Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume246, Issue3June 2012Pages 322-322 RelatedInformation

Ice Formation via Deposition Mode Nucleation on Bare and Alcohol-Covered Graphite Surfaces

Deposition of water on aerosol particles contributes to ice cloud formation in the atmosphere with implications for the water cycle and climate on Earth. The heterogeneous ice nucleation process is influenced by physico-chemical properties of the substrate, but the mechanisms remain incompletely understood. Here, we report on ice formation on bare and alcohol-covered graphite at temperatures from 175 to 213 K, probed by elastic helium and light scattering. Water has a low wettability on bare and butanol-covered graphite resulting in the growth of rough ice surfaces. In contrast, pre-adsorbed methanol provides hydrophilic surface sites and results in the formation of smooth crystalline ice; an effect that is pronounced also for sub-monolayer methanol coverages. The alcohols primarily reside at the ice surface and at the ice-graphite interface with a minor fraction being incorporated into the growing ice structures. Methanol has no observable effect on gas/solid water vapor exchange whereas butanol acts as a transport barrier for water resulting in a reduction in ice evaporation rate at 185 K. Implications for the description of deposition mode freezing are discussed.

Self-pressurized rapid freezing (SPRF) as a simple fixation method for cryo-electron microscopy of vitreous sections

Cryo-electron microscopy of vitreous sections (CEMOVIS) is currently considered the method of choice to explore cellular ultrastructure at high resolution as close as possible to their native state. Here, we apply a novel, easy-to-use and low-cost freeze fixation method for CEMOVIS, avoiding the use of high-pressure freezing apparatus. Cells are placed in capillary metal tubes, which are tightly closed and plunged directly into liquid ethane cooled by liquid nitrogen. In some parts of the tube, crystalline ice is formed, building up pressure sufficient for the liquid-glass transition of the remaining specimen. We verified the presence of vitreous ice in these preparations using CEMOVIS and electron diffraction. Furthermore, different tube materials being less poisonous than copper were established to minimize physiological alterations of the specimen. Bacteria, yeast and mammalian cells were tested for molecular resolution. The quality of results is equivalent to samples prepared by conventional high pressure freezing apparatus, thus establishing this novel method as fast, easy-to-use and low-cost freeze fixation alternative for cryo-EM.