Crystals Of Ice Ih Research Articles

The spectrum of Ih ice using terahertz time-domain spectroscopy.

Here, we report the frequency-dependent spectrum of ice Ih in the range of 0.2-2THz. We confirm the presence of a feature that blue-shifts from around 1.55-1.65THz with a decreasing temperature from 260 to 160K. There is also a change in the trend of the refractive index of ice corresponding to a dispersion, which is also around 1.6THz. The features are reproduced in data acquired with three commercial terahertz time-domain spectrometers. Computer-simulated spectra assign the feature to lattice translations perpendicular to the 110 and 1̄10 planes of the ice Ih crystal. The feature's existence should be recognized in the terahertz measurements of frozen aqueous solution samples to avoid false interpretations.

Quantification of anion and cation uptake in ice Ih crystals.

While ice has very low solubility for salts compared to water, small amounts of ions are doped into ice crystals. These small ion dopants can alter the fundamental physical and chemical properties of ice, such as its structure and electrical conductivity. Therefore, these results could have a direct impact on the chemical reactivity of ice and ice surfaces. Here, we examine the influence of the uptake of three salts-ammonium chloride (NH4Cl), sodium chloride (NaCl), and ammonium sulfate [(NH4)2SO4]-on ice Ih formation using capillary electrophoresis. Using both cation and anion modes, we observed and quantified the uptake of individual ions into the ice. Our results indicate that anions have a higher propensity for uptake into ice Ih crystals.

Transferable Potential Function for Flexible H2O Molecules Based on the Single-Center Multipole Expansion.

A potential function is presented for describing a system of flexible H2O molecules based on the single-center multipole expansion (SCME) of the electrostatic interaction. The model, referred to as SCME/f, includes the variation of the molecular quadrupole moment as well as the dipole moment with changes in bond length and angle so as to reproduce results of high-level electronic structure calculations. The multipole expansion also includes fixed octupole and hexadecapole moments, as well as anisotropic dipole-dipole, dipole-quadrupole, and quadrupole-quadrupole polarizability tensors. The model contains five adjustable parameters related to the repulsive interaction and damping functions in the electrostatic and dispersion interactions. Their values are adjusted to reproduce the lowest energy isomers of small clusters, (H2O)n with n = 2-6, as well as measured properties of the ice Ih crystal. Subsequent calculations of the energy difference between the various isomer configurations of the clusters show that SCME/f gives good agreement with results of electronic structure calculations and represents a significant improvement over the previously presented rigid SCME potential function. Analysis of the vibrational frequencies of the clusters and structural properties of ice Ih crystal show the importance of accurately describing the variation of the quadrupole moment with molecular structures.

Structures of ions accommodated in salty ice Ih crystals.

Frozen aqueous electrolytes are ubiquitous and involved in various phenomena occurring in the natural environment. Although salts are expelled from ice during freezing of aqueous solutions, minor amounts of the constituent ions are accommodated in the crystal lattice of ice. This phenomenon was associated with the generation of the Workman-Reynolds freezing potential. Molecular simulations also confirmed the ion incorporation in the crystal lattice of ice Ih upon freezing of aqueous electrolytes and identified possible local structures of the ions. However, no experimental information is available on the structure of ions accommodated in the crystal lattice of ice Ih. In this work, we use X-ray absorption fine structure (XAFS) to study the local structures of K+ and Cl- accommodated in ice Ih single crystals. Previous molecular simulations predicted that ions are trapped in the hexagonal cavities of the ice structure or replace two water molecules in the crystal lattice. Four possible configurations are considered and optimized by the calculations using ONIOM (QM/QM/QM). The results are evaluated in terms of the agreement between the experimental XAFS spectra and those simulated from the optimized structures. The spectra are most reasonably interpreted by assuming that K+ replaces one water molecule in the ice crystal lattice and is accommodated in a tetrahedral coordination cage. Similarly, Cl- probably adopts the same configuration, because it explains the coordination number better than other structures, such as that assuming the replacement of two water molecules belonging to the same hexagonal planes.

Vitrification and increase of basicity in between ice Ih crystals in rapidly frozen dilute NaCl aqueous solutions.

The freezing of ionic aqueous solutions is common in both nature and human-conducted cryopreservation. The cooling rate and the dimensions constraining the solution are known to fundamentally influence the physicochemical characteristics of the sample, including the extent of vitrification, morphology, and distribution of ions. The presence of some salts in an aqueous solution often suppresses the ice crystallization, allowing bulk vitrification during relatively slow cooling. Such a process, however, does not occur in NaCl solutions, previously observed to vitrify only under hyperquenching and/or in sub-micrometric confinements. This work demonstrates that, at freezing rates of ≥100 K min-1, crystallized ice Ih expels the freeze-concentrated solution onto the surfaces of the crystals, forming lamellae and veins to produce glass, besides eutectic crystallization. The vitrification covers (6.8% ± 0.6%) and (17.9% ± 1.5%) of the total eutectic content in 0.06M and 3.4 mM solutions, respectively. The vitrified solution shows a glass-to-liquid transition succeeded by cold crystallization of NaCl · 2H2O during heating via differential scanning calorimetry. We establish that ice crystallization is accompanied by increased basicity in freeze-concentrated solutions, reflecting preferential incorporation of chloride anions over sodium cations into the ice. After the sample is heated above the glass transition temperature, the acidity gradually returns towards the original value. The morphology of the samples is visualized with an environmental scanning electron microscope. Generally, the method of vitrifying the freeze-concentrated solution in between the ice Ih crystals via fast cooling can be considered a facile route towards information on vitrified solutions.

Why is Ice Slippery? Simulations of Shear Viscosity of the Quasi-Liquid Layer on Ice.

The temperature and depth dependence of the shear viscosity (η) of the quasi-liquid layer (QLL) of water on ice-Ih crystals was determined using simulations of the TIP4P/Ice model. The crystals display either the basal {0001} or prismatic {101̅0} facets, and we find that the QLL viscosity depends on the presented facet, the distance from the solid/liquid interface, and the undercooling temperature. Structural order parameters provide two distinct estimates of the QLL widths, which are found to range from 6.0 to 7.8 Å, and depend on the facet and undercooling temperature. Above 260 K, the viscosity of the vapor-adjacent water layer is significantly less viscous than the solid-adjacent layer and is also lower than the viscosity of liquid water.

Ice crystal growth under the presence of krypton and methane at low temperature

To investigate the influence of foreign gas inclusion on the crystallization of ice, we studied the low-temperature (74 < T < 160 K) vacuum deposition of water molecules mixed with Kr or CH4 in a wide range of H2O/gas mixing ratios (0.004 < R < 4) by means of in-situ X-ray diffraction. When H2O vapor containing either Kr or CH4 was condensed onto a cold substrate, ice Ih crystals were found to grow below 130 K in a film of amorphous solid water (ASW), whereas pure H2O gas formed only ASW below 135 K. Small to moderate concentrations (R > 0.2) of Kr and CH4 enhance the formation of ice Ih and increase the crystal size, while at high foreign gas contents (R ⩽ 0.2) that may develop Kr or CH4 crystals below 92 K, the crystal size and relative amount of ice decrease strongly. The maximum ice Ih crystal size in the order of 200 nm was observed with either Kr or CH4 at 92 K for R = 0.2. We propose that Kr and CH4 induce the crystallization of ice by acting as a surfactant.

Accurate Relative Energies and Binding Energies of Large Ice-Liquid Water Clusters and Periodic Structures.

Relative energies and binding energies are crucial quantities that determine various molecular properties of ice and water. We developed a new effective method to compute those energies of bulk ice-liquid water systems. In this work, ten ice-liquid 144-mers and ten periodic ice-liquid (H2O)64 systems are taken from the molecular dynamics simulations in the melting process of ice-Ih crystals. They are investigated at the levels of density functional theory (DFT), explicitly correlated second-order Møller-Plesset perturbation theory (MP2-F12), and coupled-cluster singles and doubles with noniterative triples corrections [CCSD(T)-F12b] in the framework of generalized energy-based fragmentation approach. Our results show that the changing of noncovalent interactions significantly influences the performances of DFT and electron correlation methods for those systems in the melting process of ice. Various DFT methods predict quite different results for ice and mixed ice-liquid structures but give similar results for pure liquid ones. It also explains why many DFT-based simulations lead to inaccurate densities of ice and liquid water. The CCSD(T)-F12b results suggest that the MP2-F12 method provides satisfactory results and is expected to be employed to simulate the phase transitions of ice crystal.

Single-crystal Ih ice surfaces unveil connection between macroscopic and molecular structure

Physics and chemistry of ice surfaces are not only of fundamental interest but also have important impacts on biological and environmental processes. As ice surfaces-particularly the two prism faces-come under greater scrutiny, it is increasingly important to connect the macroscopic faces with the molecular-level structure. The microscopic structure of the ubiquitous ice Ih crystal is well-known. It consists of stacked layers of chair-form hexagonal rings referred to as molecular hexagons. Crystallographic unit cells can be assembled into a regular right hexagonal prism. The bases are labeled crystallographic hexagons. The two hexagons are rotated 30° with respect to each other. The linkage between the familiar macroscopic shape of hexagonal snowflakes and either hexagon is not obvious per se. This report presents experimental data directly connecting the macroscopic shape of ice crystals and the microscopic hexagons. Large ice single crystals were used to fabricate samples with the basal, primary prism, or secondary prism faces exposed at the surface. In each case, the same sample was used to capture both a macroscopic etch pit image and an electron backscatter diffraction (EBSD) orientation density function (ODF) plot. Direct comparison of the etch pit image and the ODF plot compellingly connects the macroscopic etch pit hexagonal profile to the crystallographic hexagon. The most stable face at the ice-water interface is the smallest area face at the ice-vapor interface. A model based on the molecular structure of the prism faces accounts for this switch.

Sterilization by Cooling in Isochoric Conditions: The Case of Escherichia coli

High hydrostatic pressure (HHP) affects the structure, metabolism and survival of micro-organisms including bacteria. For this reason HHP is a promising treatment in the food industry. The aim of this work is to evaluate the effect of high pressure, under isochoric cooling conditions, on Escherichia coli, where such high pressure develops due to the fact water cannot expand. We combine survival curves obtained by spectrophotometry and images of atomic force microscopy in this study. Our results show that cooling at -20 and -30°C leads to a partial destruction of a Escherichia coli population. However, cooling at -15°C causes a total extermination of bacteria. This intriguing result is explained by the phase diagram of water. In the first case, the simultaneous formation of ice III and ice Ih crystals provides a safe environment for bacteria. In the second case (-15°C) Escherichia coli remains in a metastable and amorphous free-of-crystals liquid subjected to high pressure. Our work is the first experimental study carried out to inactivate Escherichia coli under isochoric cooling conditions. Unlike HHP, which is based on the application of an external load to augment the pressure, this technique only requires cooling. The method could be used for annihilation of other Escherichia coli strains and perhaps other micro-organisms.

Structural mechanisms of the Ih–II and II → Ic transitions between the crystalline phases of aqueous ice

Structural mechanisms are proposed for experimentally observed phase transitions between crystalline modifications of aqueous ice, Ih and II, as well as II and Ic. It is known that the Ih–II transition occurs with the conservation of large structural units (hexagonal channels) common for these ices. It is shown that the Ih → II transition may occur with the conservation of 5/6 of all hydrogen bonds in crystal, including all hydrogen bonds in the retained channels (3/4 of the total number of bonds in crystal) and 1/3 of the bonds between these channels (1/12 of the total number). The transformation of other hydrogen bonds between the retained channels leads to the occurrence of proton order in ice II. A structural mechanism is proposed to explain the transformation of single crystals of ice Ih either into single crystals of ice II or into crystalline twins of ice II with c axes rotated by 180° with respect to each other, which is often observed at the Ih → II transition. It is established that up to 7/12 of all hydrogen bonds are retained at the irreversible cooperative II → Ic transition.

Fluctuating Local Recrystallization of Quasi-Liquid Layer of Sub-Micrometer-Scale Ice: A Molecular Dynamics Study

Molecular dynamic simulation of a faceted ice-Ih crystal with the largest dimension of 0.06 µm in a vacuum is performed by employing the TIP4P intermolecular potential at temperatures Tm − 23, Tm − 13, and Tm − 1 K, where Tm is the melting point of the TIP4P bulk ice. We thereby observe at all the temperatures that the quasi-liquid layers (QLLs) formed on the basal (0001) surfaces are bumpy and that the liquid bumps repeatedly form and break at various places in a random manner. At Tm − 1 K, a liquid sheet appears under the liquid bumps. At an intermediate temperature for the bilayer-by-bilayer surface melting, the molecules under the local areas of either thin or thick QLLs have respectively the tendency to melt or recrystallize.

Diffuse scattering in Ih ice

Single crystals of ice Ih, extracted from the subglacial Lake Vostok accretion ice layer (3621 m depth) were investigated by means of diffuse x-ray scattering and inelastic x-ray scattering. The diffuse scattering was identified as mainly inelastic and rationalized in the frame of ab initio calculations for the ordered ice XI approximant. Together with Monte-Carlo modelling, our data allowed reconsidering previously available neutron diffuse scattering data of heavy ice as the sum of thermal diffuse scattering and static disorder contribution.

Alignment of nonmagnetic solid grains that essentially require high magnetic field; alignment of hexagonal ice Ih

Minimum field intensity required to achieve alignment of solid grains, which posses small diamagnetic anisotropy (Δχ)DIA, is discussed based on observed values of hexagonal ice Ih; the field intensity is about 6 Tesla at T = 273K for ice Ih crystal with 1.0 μm in diameter. Grain alignment essentially require strong magnetic field above several Tesla when (Δχ)DIA is in the level of 10−10 emu/g. (Δχ)DIA arises from preferential orientation of individual chemical bond with respect to a magnetic principle axis of the solid body. Hence (Δχ)DIA is negligibly small for materials with high crystal symmetry, such as crystals having a rutile, wurtzite or perovskite structure. Alignment should be studied intensively in high magnetic-field for these types of materials. Whereas alignment occurs below B = 2T for most of the unmeasured diamagnetic crystals with lower symmetry, since their (Δχ)DIA values are expected to exceed 1 × 10−9 emu/g according to the above-mentioned model; this field is produced by an ordinary electromagnet.

Vibrations of a water adlayer on Ru(0001)

Ab initio vibration spectra have been calculated for two-dimensional arrangements of intact and partially dissociated water molecules adsorbed on Ru(0001) and for an ice-Ih crystal. Dissociation of the non-hydrogen-bonding O-D bonds of a heavy-water bilayer on Ru(0001) eliminates the highest-energy O-D stretch feature, just as is seen in Denzler et al.'s (unpublished) sum frequency generation observations. Reduced zero-point energy, a consequence of replacing O-D stretch vibrations with softer Ru-D modes, stabilizes partially dissociated adlayers relative to adsorption structures made purely of intact water molecules.

First-Principles Theoretical Study of Molecular HCl Adsorption on a Hexagonal Ice (0001) Surface

A key step in the mechanism of polar ozone depletion involves the interaction of HCl with the particles that constitute polar stratospheric clouds. These particles exist as hexagonal ice Ih crystals below approximately 185 K. As a first step, we examine the binding of molecular HCl to a number of extended surface models of the basal (0001) face of hexagonal ice in addition to a cluster model representative of an unreconstructed adsorption site. Calculations are performed using gradient-corrected density-functional theory and high-order correlation methods. After correcting for zero-point energies, we estimate the molecular binding energy and enthalpy at 185 K to be 23 and 25 kJ/mol, respectively, for low (single-molecule) HCl coverage. These estimates decrease by a few kJ/mol at higher HCl coverage and are based partially on a low density of dangling surface OH groups. Our results set the stage for future studies addressing the possible ionization of molecularly adsorbed HCl using first-principles molecular dynamics.

Diffusion and Island formation on the ice Ih basal plane surface

We present theoretical calculations of the adsorption, diffusion and island formation of water admolecules on the basal plane surface of an ice Ih crystal. These are preliminary calculations based on the simple TIP4P interaction potential, a pairwise additive potential function based on point charges. At low coverage, we find that an admolecule prefers to sit at non-crystallographic sites on the surface (i.e., sites that do not fit into the ice lattice). Since ice Ih is proton disordered, no two sites are exactly the same and there is a wide range of binding energies. For some local environments the binding energy is of the order of, or even larger than, the cohesive energy. The proton disorder also results in a range of activation energies for diffusion. After mapping out a large number of diffusion barriers using the nudged elastic band method, a kinetic Monte-Carlo calculation of the diffusion at 140 K was performed. At early time, the mean squared displacement has anomalous scaling with time as is common for diffusion on random lattices. But, at longer time the scaling is normal and a diffusion coefficient can be obtained. The diffusivity is slightly larger than a recent experimental upper bound given by Brown and George. The energetics and dynamics of the formation of small islands on the ice surface have also been studied. It is found that islands up to and including pentamer are non-crystallographic, but the hexamer is crystallographic. While the formation of a crystallographic hexamer from a non-crystallographic pentamer and a new admolecule involves a complex concerted motion of all the island molecules and a large relaxation of the substrate, the activation energy for the process is estimated to be quite small, smaller than the admolecule diffusion barrier.

A helium atom scattering study of the structure and phonon dynamics of the ice surface

The structure and phonons of an ordered ice surface, prepared in situ under ultra high vacuum conditions, have been studied by high resolution helium atom scattering. The angular distributions are dominated by sharp hexagonal (1×1) diffraction peaks characteristic of a full bilayer terminated ice Ih crystal. Additional, very broad and weak, p(2.1×2.1) peaks may indicate the presence of small domains of antiphase oriented molecules. An eikonal analysis of the 1×1 peaks is compatible with either a proton disordered or a proton ordered surface with corrugations of 0.76 Å and 0.63 Å, respectively. Inelastic time-of-flight spectra reveal not only a dispersionless phonon branch reported previously at 5.9 meV, but also the first evidence for the surface Rayleigh phonons, which are reproduced well by a Born–von Kármán simulation of a full bilayer terminated ice surface using the unmodified force constants derived from neutron scattering bulk phonon measurements. Since the lattice dynamics simulations do not reproduce the dispersionless branch, it is attributed to the vibrations of single water molecules on the ice surface.

Effects of Proton Motions on the Fluorescence from 2-Naphthol-Doped Ice Ih and the Proton Ordering Transition

Fluorescence from 2-naphthol-doped ice Ih crystals was studied using a picosecond pulsed laser. Because of the incipient ESPT (excited state proton transfer) process of 2-naphthol in ice, the fluor...

Acoustic Emission in Single Crystals of Ice

The dislocation dynamics during the creep deformation of single crystals of ice Ih was studied using acoustic emission (AE) measurements. The AE activity was recorded during uniaxial compression and torsion creep tests. The results were interpreted in terms of dislocation dynamics with the help of an AE source model relating the amplitude of an acoustic event to the number of dislocations involved in the event and to their velocity. This model was first validated by a comparison between the global AE activity and the global strain rate. Then, it was possible to evaluate the density of moving dislocations during creep deformation. Two regimes were revealed. Without significant polygonization, the density of mobile dislocations, deduced from AE, was proportional to the stress, but increased much faster after polygonization, in agreement with theoretical arguments. Finally, the power law distributions observed for AE amplitudes, the slow driving process, the very large number of interacting dislocations invo...