Structure Of Water Ice Research Articles

Basic Theory of Ice Crystallization Based on Water Molecular Structure and Ice Structure.

Freezing storage is the most common method of food preservation and the formation of ice crystals during freezing has an important impact on food quality. The water molecular structure, mechanism of ice crystal formation, and ice crystal structure are elaborated in the present review. Meanwhile the methods of ice crystal characterization are outlined. It is concluded that the distribution of the water molecule cluster structure during the crystallization process directly affects the formed ice crystals' structure, but the intrinsic relationship needs to be further investigated. The morphology and distribution of ice crystals can be observed by experimental methods while simulation methods provide the possibility to study the molecular structure changes in water and ice crystals. It is hoped that this review will provide more information about ice crystallization and promote the control of ice crystals in frozen foods.

Imaging surface structure and premelting of ice Ih with atomic resolution.

Ice surfaces are closely relevant to many physical and chemical properties, such as melting, freezing, friction, gas uptake and atmospheric reaction1-8. Despite extensive experimental and theoretical investigations9-17, the exact atomic structures of ice interfaces remain elusive owing to the vulnerable hydrogen-bonding network and the complicated premelting process. Here we realize atomic-resolution imaging of the basal (0001) surface structure of hexagonal water ice (ice Ih) by using qPlus-based cryogenic atomic force microscopy with a carbonmonoxide-functionalized tip. We find that the crystalline ice-Ih surface consists of mixed Ih- and cubic (Ic)-stacking nanodomains, forming periodic superstructures. Density functional theory reveals that this reconstructed surface is stabilized over the ideal ice surface mainly by minimizing the electrostatic repulsion between dangling OH bonds. Moreover, we observe that the ice surface gradually becomes disordered with increasing temperature (above 120 Kelvin), indicating the onset of the premelting process. The surface premelting occurs from the defective boundaries between the Ih and Ic domains and can be promoted by the formation of a planar local structure. These results put an end to the longstanding debate on ice surface structures and shed light on the molecular origin of ice premelting, which may lead to a paradigm shift in the understanding of ice physics and chemistry.

Structure of crystalline water ice formed through neon matrix sublimation under cryogenic and vacuum conditions.

Ice I has three forms depending on the stacking arrangements of its layers: hexagonal ice Ih, cubic ice Ic, and stacking disordered ice Isd. Below ∼60K, amorphous water becomes metastable, and the formation of any form of ice I is often implicitly precluded. Using a newly developed low-temperature reflection high-energy electron diffraction (RHEED) technique, we show that crystalline ice with cubic stacking sequences (i.e., ice Ic) formed through Ne sublimation from a solid H2O/Ne (1:1000 ratio) matrix at 13K. The extent of stacking disorder (disordered cubic and hexagonal stacking sequences) in the ice formed by Ne matrix sublimation is smaller than that in vapor-deposited ice Isd prepared at 143K and below the limit of detection of low-temperature RHEED. Dependence of the resulting ice structures on the thickness of the H2O/Ne matrix shows that amorphous water first forms in the early stages of Ne sublimation, and the cubic stacking sequence subsequently takes place. As the cubic ice Ic formed here at a much lower temperature (13K) than previously observed (typically above 78K), Ne matrix sublimation represents a novel route to the formation of cubic ice Ic under low-temperature and low-pressure conditions.

The north polar basal unit of Mars: An Amazonian record of surface processes and climate events

The basal unit is a sedimentary deposit of water ice and lithic fines lying within the Planum Boreum of Mars. It can be divided into two subunits, rupēs and cavi, based on their stratigraphy and age. The basal unit lies between Late Hesperian and very recent (<4 Ma) units, and thus likely represents a record of polar geologic processes and climate events spanning large portions of the Amazonian Period. Despite the numerous recent studies, several key questions remain unanswered regarding its stratigraphic nature, age, and potential as a historical record of surface processes and climate. In this study, we combine the ability of the Shallow Radar (SHARAD) to reveal the large-scale stratigraphy and morphology of the basal unit within Planum Boreum with geologic mapping of visible exposures based on high-resolution imagery. This integrated study reveals that the basal unit has significantly larger extent but smaller volume than previously thought, and demonstrates that radar profiles acquired by SHARAD can provide the necessary stratigraphic correlation to comprehensively study isolated outcrops with high-resolution imagery that would otherwise lack important context. SHARAD also reveals portions of the contact between the rupēs and cavi unit in the innermost region of Planum Boreum which will allow us to better constrain the relative volume of the two units, and thus their water ice and lithic sediment content. New age constraints on the rupēs and cavi unit reveal a history of lithic fines and water ice accumulation and erosion spanning most of the Amazonian Period. Detailed mapping of the basal unit surface morphology underneath the North Polar Layered Deposits provides further insight on the erosional history of the rupēs and cavi units and suggest a more complex resurfacing history than previously thought, likely characterized by an intimate interplay with polar ice growth and retreat. SHARAD also reveals erosional forms in the cavi unit that provide new supporting observations of its hypothesized water ice and sand-sheet structure, confirming that it likely preserved former polar cap ice in its interior.

Numerical Simulation of Subsurface Penetrating Radar in Isidis Planitia on Mars for China’s First Mission to Mars

The water ice exploration mission is an important scientific target of China’s first Mission to Mars. The high frequency full polarimetric subsurface penetrating radar (SPR) system onboard the landing rover can carry out high-resolution imaging of the near-surface area of Mars, which is an important tool for detecting the presence of shallow water ice and soil structure. At present, most of the radar detection simulations are based on low-frequency antennas to analyze the geological structure of Mars down to several kilometers, with low resolution, which is difficult to detect the subsurface structure in the near-surface accurately. Considering topographic relief, interface roughness, subsurface rock, water ice, and permittivity changes at different layers, a three-dimensional near-surface model in the Isidis Planitia on Mars is established. The interpretation of the forward simulation results is of reference value for future Mars exploration missions.

Strong Variability of Martian Water Ice Clouds During Dust Storms Revealed From ExoMars Trace Gas Orbiter/NOMAD

AbstractObservations of water ice clouds and aerosols on Mars can provide important insights into the complexity of the water cycle. Recent observations have indicated an important link between dust activity and the water cycle, as intense dust activity can significantly raise the hygropause, and subsequently increase the escape of water after dissociation in the upper atmosphere. Here present observations from Nadir and Occultation for MArs Discovery/Trace Gas Orbiter that investigate the variation of water ice clouds in the perihelion season of Mars year 34 (April 2018–2019), their diurnal and seasonal behavior, and the vertical structure and microphysical properties of water ice and dust. These observations reveal the recurrent presence of a layer of mesospheric water ice clouds subsequent to the 2018 global dust storm. We show that this layer rose from 45 to 80 km in altitude on a time scale of days from heating in the lower atmosphere due to the storm. In addition, we demonstrate that there is a strong dawn‐dusk asymmetry in water ice abundance, related to nighttime nucleation and subsequent daytime sublimation. Water ice particle sizes are retrieved consistently and exhibit sharp vertical gradients (from 0.1 to 4.0 μm), as well as mesospheric differences between the global dust storm (&lt;0.5 μm) and the 2019 regional dust storm (1.0 μm), which suggests differing water ice nucleation efficiencies. These results form the basis to advance our understanding of mesospheric water ice clouds on Mars, and further constrain the interactions between water ice and dust in the middle atmosphere.

Study on the Structure Model of Water Molecule and the Reasons of Formation of Some Characteristics of Liquid &amp; Solid Water

A model for water (H2O) molecule, the structure of ice, snow and liquid water were presented, and the reasons of formation of their specific characteristics were modeled in good coincidence with observed data. (1) A stable quasi rigid molecule structure may be constructed by dominant trajectories of electrons round and between the H-O-H nucleus according with the laws of Columb’s force and Kepler’s movement rule. The core of the water molecule is a isosceles triangle with ratio of distances between nucleus: (H-H)2/(H-O)2=2.5, which would be surrounded by moving electrons and form an equilateral triangular pyramid (ETP Model) with 2 pairs of “+/-” electricity endpoints and edge length of 0.48017nm. (2) The “+/-” endpoint of a water molecule may attract other “-/+” endpoint in distance of less than 0.27 nm. A molecule may joints other molecule to have all their 4 planes parallel each other and the 6 molecules may joint as a hexagon loop with a common plane and then these loops may similarly be formed for each plane of the pyramid and extend to whole space and form the water ice structure with Zigzag Hexagon Tunnel-Vacancy System (ZHTVS Model) with porosity of ≥2.28. (3) A “sheet model” of desublimation like the snowflake is more possible phenomenon below 0°C in air, possessing the self-similarity with the hexagon-sexangle-six needle forms. (4) The liquid water has the same structure of the solid ice, but because there is 1/11 possibility to have an appearance of double electrons at one endpoint of the pyramid with “-” charge, so when the temperature is above 0°C, a part of water molecules on the frame may possess the energy for separating from the frame, and will move into the tunnel/vacancy, being as a “free water molecule”. The total volume of the liquid water would decrease until to 4°C to the minimum. The ratio of density of solid water ice and liquid water is 11/12=0.916667. (5) The relationships of the specific characteristics of the water with its construction, such as density, expansibility, compressibility, specific heat capacity, electric and thermal conductivity, solubility for O2, H2S, NaCl, KCl, etc. were discussed and numerical modeled. The experiments of saturated solution of NaCl audio-visual indicated that there are tunnel/vacancy spaces for storing NaCl molecules/ions, and increasing the volume of 1/11 of water volume after freezing. (6) The surface structure of liquid water and the applications of research results are presented in other papers.

Theoretical investigation of methanol formation from methane water-ice cluster following ionization

In this article, I have presented quantum mechanical treatment of methanol formation reaction from methane water-ice cluster after ionization with high energy photons. To mimic water ice structure, six water molecules are arranged in hexagonal form. This is the most stable structure formed by six water molecules. Theoretical photodesorption study has been performed on this structure. I have investigated a unique reaction mechanism of methanol formation from methane water ice cluster. I have shown that methanol forms after ionization via two transition states. Hydrogen molecule forms as one of the side product. Initiation of the reaction occurs by dissociation of OH bond in the water cluster followed by CH bond dissociation and formation of CO bond. The timescale of the initial step, which is dissociation of OH bond, has been computed as 50 femtosecond in this article.

Magnetospheric considerations for solar system ice state

The current lattice configuration of the water ice on the surfaces of the inner satellites of Jupiter and Saturn is likely shaped by many factors. But laboratory experiments have found that energetic proton irradiation can cause a transition in the structure of pure water ice from crystalline to amorphous. It is not known to what extent this process is competitive with other processes in solar system contexts. For example, surface regions that are rich in water ice may be too warm for this effect to be important, even if the energetic proton bombardment rate is very high. In this paper, we make predictions, based on particle flux levels and other considerations, about where in the magnetospheres of Jupiter and Saturn the ∼MeV proton irradiation mechanism should be most relevant. Our results support the conclusions of Hansen and McCord (2004), who related relative level of radiation on the three outer Galilean satellites to the amorphous ice content within the top 1 mm of surface. We argue here that if magnetospheric effects are considered more carefully, the correlation is even more compelling. Crystalline ice is by far the dominant ice state detected on the inner Saturnian satellites and, as we show here, the flux of bombarding energetic protons onto these bodies is much smaller than at the inner Jovian satellites. Therefore, the ice on the Saturnian satellites also corroborates the correlation.

The ice phenomena dynamics of small anthropogenic water bodies in the Silesian Upland, Poland

Abstract The aim of this study was to determine the dynamics of the process of a course of ice creation phenomena in two small water bodies located in the Silesian Upland. The studies and observations of ice formation on the water bodies were conducted during the period 10th November 2011 to 23rd March 2012. The following parameters were determined each day: degree of ice coverage on each water body, thickness and ice structure and thickness of snow cover on each water body. From the studies it results that a course of the ice formation of both water bodies was almost identical. The same maximum ice thickness was recorded in both cases. It was 36 cm in that season, with slight differences in average thickness. The course of particular phases of ice formation in different water regions was also very similar. The number of days with the ice phenomena and the number of days from the beginning to the end of the ice phenomena were identical in both cases, being 96 and 131 days, respectively. The slight differences over several days were recorded in the case of: number of days with shore ice (lb), number of days with partial ice cover (lcz), number of days with an incomplete ice cover (lnp), number of breaks in the ice cover (B). Additionally, with daily measurements of ice cover thickness the relationships between the course of the average daily air temperature from the meteorological station of Faculty of Earth Sciences of University of Silesia and the daily changes in the ice thickness in the water regions in question were determined by using Spearman’s correlation coefficient. In both cases the relationships were strong and they were r= −0,84(p&lt;0,001) for the Amendy water body and r= −0,87 (p&lt;0,001) for the Żabie Doły S water body. The maximum and average ice thickness, duration of the ice phenomena and ice cover and the obtained correlation coefficients between the air temperature and the changes in the ice thickness show that the water bodies in question are characterized by a quasi-natural ice regime.

Unveiling subsurface hydrogen-bond structure of hexagonal water ice

The phase-resolved sum-frequency-generation (SFG) spectrum for the basal face of hexagonal ice is reported and is interpreted by molecular dynamics simulations combined with ab initio quantum calculations. Here, we demonstrate that the line shape of the SFG spectra of isotope-diluted OH chromophores is a sensitive indicator of structural rumpling uniquely emerging at the subsurface of hexagonal ice. In the outermost subsurface between the first (B1) and second (B2) bilayer, the hydrogen bond of ${\mathrm{O}}_{\mathrm{B}1}\ensuremath{-}\mathrm{H}\ensuremath{\cdots}{\mathrm{O}}_{\mathrm{B}2}$ is weaker than that of ${\mathrm{O}}_{\mathrm{B}1}\ensuremath{\cdots}\mathrm{H}\ensuremath{-}{\mathrm{O}}_{\mathrm{B}2}$ . This implies that subsurface O-O distance is laterally altered, depending on the direction of O-H bond along the surface normal: H-up or H-down, which is in stark contrast to bulk hydrogen bonds. This new finding uncovers how water molecules undercoordinated at the topmost surface influence on the subsurface structural rumpling associated with orientational frustration inherent in water ice.

IR Selective Irradiations of Amorphous Solid Water Dangling Modes: Irradiation vs Annealing Effects

Amorphous solid water (ASW) is one of the most widely studied molecular systems. Ubiquitous in the interstellar medium (ISM) and potentially present in the upper layers of the Earth’s atmosphere, ASW plays a major role in heterogeneous physical chemistry. Small molecules form or accrete at the ice surface, bonding to water molecules with an OH bond projecting from the surface, so-called “dangling bonds”. These dangling OH are of crucial importance in the quest to identify and quantify surface reactions. Water ices in the ISM or Earth’s atmosphere undergo constant processing by thermal and irradiation effects, which can significantly affect both the bulk and surface structures and therefore the catalytic properties of the surface. In this work we have studied thermal and irradiation processing of ASW and determine that there is a photochemical processing pathway of the ice surface which is clearly distinct from purely thermal effects. Selective IR irradiations of each of the surface water modes led to the observation of a “hole-burning” at the irradiation frequency, counterbalanced by the production of a new band, identified as a water monomer interacting with the surface. The thermal effects, meanwhile, led to a global decrease of all the dangling modes due to global reorganization of the water ice structure. It is thus obvious that, depending on the processing history of an ice, its catalytic properties will not be affected in the same way. The fact that we observe an IR selective irradiation effect illustrates that some fraction of the vibrational energy, rather than being relaxed through the H-bonded network of the bulk ice, is trapped at the surface; this energy induces a reorganization of the surface structure, forming new trapping sites, and thus generating new catalytic properties.

How to link the relative abundances of gas species in coma of comets to their initial chemical composition?

Comets are expected to be the most primitive objects in the Solar System. The chemical composition of these objects is frequently assumed to be directly provided by the observations of the abundances of volatile molecules in the coma. The present work aims to determine the relationship between the chemical composition of the coma, the outgassing profile of volatile molecules and the internal chemical composition, and water ice structure of the nucleus, and physical assumptions on comets. To do this, we have developed a quasi 3D model of a cometary nucleus which takes into account all phase changes and water ice structures (amorphous, crystalline, clathrate, and a mixture of them); we have applied this model to the Comet 67P/Churyumov-Gerasimenko, the target of the Rosetta mission. We find that the outgassing profile of volatile molecules is a strong indicator of the physical and thermal properties (water ice structure, thermal inertia, abundances, distribution, physical differentiation) of the solid nucleus. Day/night variations of the rate of production of species helps to distinguish the clathrate structure from other water ice structures in nuclei, implying different thermodynamic conditions of cometary ice formation in the protoplanetary disc. The relative abundance (to H2O) of volatile molecules released from the nucleus interior varies by some orders of magnitude as a function of the distance to the Sun, the volatility of species, their abundance and distribution between the ”trapped” and ”condensed” states, the structure of water ice, and the thermal inertia and other physical assumptions (dust mantle, …) on the nucleus. For the less volatile molecules such as CO2 and H2S, the relative (to H2O) abundance of species in coma remain similar to the primitive composition of the nucleus (relative deviation less than 25%) only around the perihelion passage (in the range −3 to −2 to +2–3AU), whatever is the water ice structure and chemical composition, and under the conditions that the nucleus is not fully covered by a dust mantle. The relative (to H2O) abundance of highly volatile molecules such as CO and CH4 in the coma remain approximately equal to the primitive nucleus composition only for nuclei made of clathrates. The nucleus releases systematically lower relative abundances of highly volatile species (up to one order of magnitude) around perihelion (in the range −3 to −2 to +2–3AU) in the cases of the crystalline and amorphous water ice structures in the nuclei. The rate of production, the outgassing profile and the relative abundances (to H2O) of volatile molecules are the key parameters allowing one to retrieve the chemical composition and thermodynamic conditions of cometary ice formation in the early Solar System. The coming observations of the coma and nucleus by the Rosetta mission instruments (VIRTIS, MIRO, …) should provide the necessary constraints to the model to allow it to infer the primordial ice structure and composition of the comet.

Intracellular ice and cell survival in cryo-exposed embryonic axes of recalcitrant seeds of Acer saccharinum: an ultrastructural study of factors affecting cell and ice structures.

Cryopreservation is the only long-term conservation strategy available for germplasm of recalcitrant-seeded species. Efforts to cryopreserve this form of germplasm are hampered by potentially lethal intracellular freezing events; thus, it is important to understand the relationships among cryo-exposure techniques, water content, structure and survival. Undried embryonic axes of Acer saccharinum and those rapidly dried to two different water contents were cooled at three rates and re-warmed at two rates. Ultrastructural observations were carried out on radicle and shoot tips prepared by freeze-fracture and freeze-substitution to assess immediate (i.e. pre-thaw) responses to cooling treatments. Survival of axes was assessed in vitro. Intracellular ice formation was not necessarily lethal. Embryo cells survived when crystal diameter was between 0·2 and 0·4 µm and fewer than 20 crystals were distributed per μm(2) in the cytoplasm. Ice was not uniformly distributed within the cells. In fully hydrated axes cooled at an intermediate rate, the interiors of many organelles were apparently ice-free; this may have prevented the disruption of vital intracellular machinery. Intracytoplasmic ice formation did not apparently impact the integrity of the plasmalemma. The maximum number of ice crystals was far greater in shoot apices, which were more sensitive than radicles to cryo-exposure. The findings challenge the accepted paradigm that intracellular ice formation is always lethal, as the results show that cells can survive intracellular ice if crystals are small and localized in the cytoplasm. Further understanding of the interactions among water content, cooling rate, cell structure and ice structure is required to optimize cryopreservation treatments without undue reliance on empirical approaches.

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.

Lunar radiation environment and space weathering from the Cosmic Ray Telescope for the Effects of Radiation (CRaTER)

The Cosmic Ray Telescope for the Effects of Radiation (CRaTER) measures linear energy transfer by Galactic Cosmic Rays (GCRs) and Solar Energetic Particles (SEPs) on the Lunar Reconnaissance Orbiter (LRO) Mission in a circular, polar lunar orbit. GCR fluxes remain at the highest levels ever observed during the space age. One of the largest SEP events observed by CRaTER during the LRO mission occurred on June 7, 2011. We compare model predictions by the Earth‐Moon‐Mars Radiation Environment Module (EMMREM) for both dose rates from GCRs and SEPs during this event with results from CRaTER. We find agreement between these models and the CRaTER dose rates, which together demonstrate the accuracy of EMMREM, and its suitability for a real‐time space weather system. We utilize CRaTER to test forecasts made by the Relativistic Electron Alert System for Exploration (REleASE), which successfully predicts the June 7th event. At the maximum CRaTER‐observed GCR dose rate (∼11.7 cGy/yr where Gy is a unit indicating energy deposition per unit mass, 1 Gy = 1 J/kg), GCRs deposit ∼88 eV/molecule in water over 4 billion years, causing significant change in molecular composition and physical structure (e.g., density, color, crystallinity) of water ice, loss of molecular hydrogen, and production of more complex molecules linking carbon and other elements in the irradiated ice. This shows that space weathering by GCRs may be extremely important for chemical evolution of ice on the Moon. Thus, we show comprehensive observations from the CRaTER instrument on the Lunar Reconnaissance Orbiter that characterizes the radiation environment and space weathering on the Moon.

Pressure dependent trace gas trapping in amorphous water ice at 77 K: Implications for determining conditions of comet formation

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 77K. 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.

Structure and dynamics of the Martian lower and middle atmosphere as observed by the Mars Climate Sounder: Seasonal variations in zonal mean temperature, dust, and water ice aerosols

The first Martian year and a half of observations by the Mars Climate Sounder aboard the Mars Reconnaissance Orbiter has revealed new details of the thermal structure and distributions of dust and water ice in the atmosphere. The Martian atmosphere is shown in the observations by the Mars Climate Sounder to vary seasonally between two modes: a symmetrical equinoctial structure with middle atmosphere polar warming and a solstitial structure with an intense middle atmosphere polar warming overlying a deep winter polar vortex. The dust distribution, in particular, is more complex than appreciated before the advent of these high (∼5 km) vertical resolution observations, which extend from near the surface to above 80 km and yield 13 dayside and 13 nightside pole‐to‐pole cross sections each day. Among the new features noted is a persistent maximum in dust mass mixing ratio at 15–25 km above the surface (at least on the nightside) during northern spring and summer. The water ice distribution is very sensitive to the diurnal and seasonal variation of temperature and is a good tracer of the vertically propagating tide.

A polarizable, four-point-charge model of water with size variation

The proposed model is classical, polarizable and can change its size responding to the impact of the surroundings. We introduce a qualitative theory which simultaneously changes polarization, repulsion and size. Larger electric fields in condensed phases pull the molecules closer and induce larger polarization than in gas phase. However, this causes exponential increase in repulsion as a result of overlapping electron clouds. To decrease the impact of this repulsion the electron cloud contracts slightly, which decrease its polarization. Since the size of the molecule is determined by the extension of its electron cloud, there will be a subtle equilibrium determined by the actual strength of the polarization force, the repulsion and the size of the molecule. Using the principles above, we developed a model and carried out numerical calculations. The properties of the dimer practically reproduce the experimental values. The estimates of the energy, the density and the structure of liquid water and hexagonal ice are also excellent.

A local-MP2 approach to the ab initio study of electron correlation in crystals and to the simulation of vibrational spectra: the case of Ice XI

Wave-function-based computational techniques for describing electron correlation effects in periodic systems have a long history. Among early attempts, the method proposed by Colle and Salvetti (Theor Chim Acta 37:329, 1975) more than 30 years ago is noteworthy for its simplicity, power, and far-reaching consequences. The renewed interest in this topic is due to the well-known failure of techniques based on Density Functional Theory when it comes to obtaining very accurate estimates of some important quantities. Here we present the essential features of an ab initio code, (CRYSCOR) recently implemented (Phys Rev B 76: 075101, 075102, 2007), which solves the MP2 equations for crystals by adopting a local-correlation approach and using as a reference the Hartree-Fock solution provided by the CRYSTAL program. As an example of application, we discuss the MP2 corrections to the frequency of some vibrational modes in a proton-ordered structure of water ice (Ice XI).