DOCSLIB.ORG

Structural Transformations in Amorphous Ice and Supercooled Water and Their Relevance to the Phase Diagram of Water Alan K Soper

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Structural Transformations in Amorphous Ice and Supercooled Water and Their Relevance to the Phase Diagram of Water Alan K Soper Structural transformations in amorphous ice and supercooled water and their relevance to the phase diagram of water Alan K Soper To cite this version: Alan K Soper. Structural transformations in amorphous ice and supercooled water and their relevance to the phase diagram of water. Molecular Physics, Taylor & Francis, 2008, 106 (16-18), pp.2053-2076. 10.1080/00268970802116146. hal-00513204 HAL Id: hal-00513204 https://hal.archives-ouvertes.fr/hal-00513204 Submitted on 1 Sep 2010 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Molecular Physics For Peer Review Only Structural transformations in amorphous ice and supercooled water and their relevance to the phase diagram of water Journal: Molecular Physics Manuscript ID: TMPH-2008-0088 Manuscript Type: Invited Article Date Submitted by the 17-Mar-2008 Author: Complete List of Authors: Soper, Alan supercooled water, amorphous ice, structure, second critical point, Keywords: computer simulation URL: http://mc.manuscriptcentral.com/tandf/tmph Page 1 of 36 Molecular Physics 1 2 Structural transformations in amorphous ice and supercooled water and their 3 relevance to the phase diagram of water 4 5 A.K.Soper∗ 6 ISIS Facility, STFC Rutherford Appleton Laboratory, 7 Harwell Science and Innovation Campus, Didcot, Oxon, OX11 0QX, UK 8 (Dated: March 17, 2008) 9 Arguably the most important liquid in our existence, water continues to attract enormous efforts 10 to understand its underlying structure, dynamics and thermodynamics. These properties become 11 increasingly complex and controversial as we progress into and below the “no man’s land” where 12 bulk water can only exist as crystalline ice. Various, so far unconfirmed, scenarios are painted 13 for this region, including the second critical point scenario, the singularity-free scenario, and most Science 319 14 recently the “critical point-free” scenario [C.A. Angell, , , 582 (2008)]. In this article the structural aspects of water (as opposed to its dynamic and thermodynamic properties) in its 15 supercooled, amorphous and confined states are explored, to the extent that these are known and 16 related toFor the water phasePeer diagram. AnReview important issue to emerge Only is the extent to which structural 17 measurements on a disordered material can tell us about its phase. 18 19 20 I. INTRODUCTION competing scenarios for understanding the properties of 21 supercooled and glassy water. One of these was the pro- 22 Figure 1 shows a simplified phase diagram of water in posal that at a temperature of around 220K and pressure 23 the ambient and low temperature region. In particular of 0.1GPa, water exhibited a second critical point below 24 it is seen that, starting from ambient pressure, the melt- which it separated into one of two distinct forms, high 25 ing point falls to about 251K at a pressure of 0.2GPa, density liquid (HDL) and low density liquid (LDL), with 26 then rises to higher temperatures with further increases a first order transformation between them. These liquids 27 in pressure. Below the equilibrium melting line lies the were a continuous extension of their much lower temper- 28 homogeneous nucleation line - this is the lowest temper- ature amorphous counterparts, HDA and LDA respec- 29 ature to which the liquid can be cooled before sponta- tively. The increase in density and entropy fluctuations 30 neous crystallisation sets in: the bulk liquid cannot exist as one approached this critical point could be used ex- 31 below this line. At ambient pressure it occurs at 231K. plain the increased compressibility and heat capacity of 32 At much lower temperatures, below 150K, water can be water on cooling water below its stable melting temper- 33 made to form an amorphous solid, either by condensing ature. The consequences of such a second critical point 34 water vapour onto a cold substrate, or by hyperquenching would extend up into the accessible supercooled and low temperature stable liquid regions. Hence there is for ex- 35 droplets of the liquid, or by pressurising crystalline ice to ample a marked but continuous structural transforma- 36 around 1GPa. The material made by the latter process tion between HDL and LDL in the low temperature sta- 37 is actually a high density form of amorphous ice, called ble liquid region [3]. However the difficulty of observing 38 HDA: when the pressure is released it converts spon- this second critical point in the bulk liquid, or even get- 39 taneously to the low density form, LDA, which, struc- ting close to it, means it is ‘virtual’ in the same sense that 40 turally at least, appears very similar to the amorphous the focal point of a concave lens is virtual, namely you 41 ices formed by vapour deposition and hyperquenching. might be able to see the effects of the postulated second 42 Subsequently an even denser form of amorphous ice was found, VHDA, formed by annealing HDA under pressure critical point in the stable liquid region, even though you 43 can’t observe it directly. 44 at 120K. When the pressure is released VHDA converts This means its existence will remain controversial, 45 directly to LDA and does not stop at HDA on the way, since there is also the “singularity free” scenario, which 46 so there is a debate about whether VHDA is truly a new reports a similar phase diagram to that with the second 47 form of amorphous ice, or whether it is simply densified, critical point, but without any divergences in thermody- 48 annealed HDA. The space (shaded in Fig. 1) between the highest amorphous ice formation temperature, TX , namic quantities and with a rapid but continuous trans- 49 formation between HDL and LDL. Within this scenario 50 and the homogeneous nucleation line, TH , is often called “no man’s land” since experiments on the bulk liquid in the transition from HDA to LDA would also be rapid but 51 that region are impossible. continuous. 52 More recently, Angell [4, 5] has proposed, in analogy 53 Comprehensive and very readable reviews of the cur- to what happens in crystalline C , the hypothesis of an 54 rent state of thinking on supercooled water were pub- 60 lished in 2003.[1, 2] At that time there appeared to be two order-disorder transition occurring as deeply cooled wa- 55 ter is heated, this transition occurring also at 225K. Such 56 a transition is apparently observed in highly confined wa- 57 ter, where the freezing transition is suppressed. It does 58 ∗[email protected] not exclude the second critical point scenario, but it also 59 60 URL: http://mc.manuscriptcentral.com/tandf/tmph Molecular Physics Page 2 of 36 2 1 2 does not require it. How this most recent suggestion re- bulk water, which had generally been more or less under- 3 lates to the full phase diagram of cold water remains to stood for many years as a tetrahedrally coordinated net- 4 be determined. work, was thrown into disarray in 2004 [14] with the chal- 5 It is interesting that in 1997 Jeffery and Austin, [10], lenging, and so far unconfirmed, proposition that water in 6 published an equation of state that they claimed was sig- fact was more chain-like than network-like. Independent 7 nificantly more accurate than existing equations of state evidence in support of this idea is still lacking, and the 8 for water. Extrapolating this phase diagram into the su- interpretation of the x-ray absorption spectroscopy data 9 percooled region, they refer to a second critical point for that led to the original proposal is controversial and not fully understood. Nonetheless the proposal has led to a 10 water and the likelihood of a high density to low density substantial amount of research trying to corroborate or 11 transition which occurs immediately before freezing at understand the findings. 12 high enough pressures. These ideas were elaborated in In this situation it is not possible in a review of this 13 a subsequent paper, [12]. In the meantime Mishima and kind to cover all the topics related to water with any de- 14 Stanley in 1998 observed a discontinuity in the decom- gree of completeness. Instead the aim is to summarise as 15 pression induced melting line of ice IV and concluded this best as possible the primary structural aspects of ambient 16 could mean there wasFor a second criticalPeer point at aboutReview the Only and supercooled water and amorphous ice, to the extent 17 same pressure and temperature as Jeffery and Austin, that these are understood, and to identify discrepancies 18 namely 0.1GPa and 220K, [11]. They do not refer to between different accounts. Reference to computer sim- 19 the Jeffery and Austin equation of state, but the latter ulations of water will only be made where relevant, since 20 appears to derive from previous work, [13], so it is not clear how truly independent are the two results. Even so the computer simulation of water is itself a vast topic 21 it seems curious that a very accurate equation of state that could not possibly be given adequate coverage here. 22 seems to predict the same behaviour as the observed Although computer simulations of water and other mate- 23 ice IV melting curve.
Load more

Recommended publications
  • Ice Ic” Werner F
    Extent and relevance of stacking disorder in “ice Ic” Werner F. Kuhsa,1, Christian Sippela,b, Andrzej Falentya, and Thomas C. Hansenb aGeoZentrumGöttingen Abteilung Kristallographie (GZG Abt. Kristallographie), Universität Göttingen, 37077 Göttingen, Germany; and bInstitut Laue-Langevin, 38000 Grenoble, France Edited by Russell J. Hemley, Carnegie Institution of Washington, Washington, DC, and approved November 15, 2012 (received for review June 16, 2012) “ ” “ ” A solid water phase commonly known as cubic ice or ice Ic is perfectly cubic ice Ic, as manifested in the diffraction pattern, in frequently encountered in various transitions between the solid, terms of stacking faults. Other authors took up the idea and liquid, and gaseous phases of the water substance. It may form, attempted to quantify the stacking disorder (7, 8). The most e.g., by water freezing or vapor deposition in the Earth’s atmo- general approach to stacking disorder so far has been proposed by sphere or in extraterrestrial environments, and plays a central role Hansen et al. (9, 10), who defined hexagonal (H) and cubic in various cryopreservation techniques; its formation is observed stacking (K) and considered interactions beyond next-nearest over a wide temperature range from about 120 K up to the melt- H-orK sequences. We shall discuss which interaction range ing point of ice. There was multiple and compelling evidence in the needs to be considered for a proper description of the various past that this phase is not truly cubic but composed of disordered forms of “ice Ic” encountered. cubic and hexagonal stacking sequences. The complexity of the König identified what he called cubic ice 70 y ago (11) by stacking disorder, however, appears to have been largely over- condensing water vapor to a cold support in the electron mi- looked in most of the literature.
    [Show full text]
  • Indiana Glaciers.PM6
    How the Ice Age Shaped Indiana Jerry Wilson Published by Wilstar Media, www.wilstar.com Indianapolis, Indiana 1 Previiously published as The Topography of Indiana: Ice Age Legacy, © 1988 by Jerry Wilson. Second Edition Copyright © 2008 by Jerry Wilson ALL RIGHTS RESERVED 2 For Aaron and Shana and In Memory of Donna 3 Introduction During the time that I have been a science teacher I have tried to enlist in my students the desire to understand and the ability to reason. Logical reasoning is the surest way to overcome the unknown. The best aid to reasoning effectively is having the knowledge and an understanding of the things that have previ- ously been determined or discovered by others. Having an understanding of the reasons things are the way they are and how they got that way can help an individual to utilize his or her resources more effectively. I want my students to realize that changes that have taken place on the earth in the past have had an effect on them. Why are some towns in Indiana subject to flooding, whereas others are not? Why are cemeteries built on old beach fronts in Northwest Indiana? Why would it be easier to dig a basement in Valparaiso than in Bloomington? These things are a direct result of the glaciers that advanced southward over Indiana during the last Ice Age. The history of the land upon which we live is fascinating. Why are there large granite boulders nested in some of the fields of northern Indiana since Indiana has no granite bedrock? They are known as glacial erratics, or dropstones, and were formed in Canada or the upper Midwest hundreds of millions of years ago.
    [Show full text]
  • Genesis and Geographical Aspects of Glaciers - Vladimir M
    HYDROLOGICAL CYCLE – Vol. IV - Genesis and Geographical Aspects of Glaciers - Vladimir M. Kotlyakov GENESIS AND GEOGRAPHICAL ASPECTS OF GLACIERS Vladimir M. Kotlyakov Institute of Geography, Russian Academy of Sciences, Moscow, Russia Keywords: Chionosphere, cryosphere, equilibrium line, firn line, glacial climate, glacier, glacierization, glaciosphere, ice, seasonal snow line, snow line, snow-patch Contents 1. Introduction 2. Properties of natural ice 3. Cryosphere, glaciosphere, chionosphere 4. Snow-patches and glaciers 5. Basic boundary levels of snow and ice 6. Measures of glacierization 7. Occurrence of glaciers 8. Present-day glacierization of the Arctic Glossary Bibliography Biographical Sketch Summary There exist ten crystal variants of ice and one amorphous form in Nature, however only one form ice-1 is distributed on the Earth. Ten other ice variants steadily exist only under a certain combinations of pressure, specific volume and temperature of medium, and those are not typical for our planet. The ice density is less than that of water by 9%, and owing to this water reservoirs are never totally frozen., Thus life is sustained in them during the winter time. As a rule, ice is much cleaner than water, and specific gas-ice compounds called as crystalline hydrates are found in ice. Among the different spheres surrounding our globe there are cryosphere (sphere of the cold), glaciosphere (sphere of snow and ice) and chionosphere (that part of the troposphere where the annual amount of solid precipitation exceeds their losses). The chionosphere envelopes the Earth with a shell 3 to 5 km in thickness. In the present epoch, snow and ice cover 14.2% of the planet’s surface and more than half of the land surface.
    [Show full text]
  • Case Fil Copy
    NASA TECHNICAL NASA TM X-3511 MEMORANDUM CO >< CASE FIL COPY REPORTS OF PLANETARY GEOLOGY PROGRAM, 1976-1977 Compiled by Raymond Arvidson and Russell Wahmann Office of Space Science NASA Headquarters NATIONAL AERONAUTICS AND SPACE ADMINISTRATION • WASHINGTON, D. C. • MAY 1977 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. TMX3511 4. Title and Subtitle 5. Report Date May 1977 6. Performing Organization Code REPORTS OF PLANETARY GEOLOGY PROGRAM, 1976-1977 SL 7. Author(s) 8. Performing Organization Report No. Compiled by Raymond Arvidson and Russell Wahmann 10. Work Unit No. 9. Performing Organization Name and Address Office of Space Science 11. Contract or Grant No. Lunar and Planetary Programs Planetary Geology Program 13. Type of Report and Period Covered 12. Sponsoring Agency Name and Address Technical Memorandum National Aeronautics and Space Administration 14. Sponsoring Agency Code Washington, D.C. 20546 15. Supplementary Notes 16. Abstract A compilation of abstracts of reports which summarizes work conducted by Principal Investigators. Full reports of these abstracts were presented to the annual meeting of Planetary Geology Principal Investigators and their associates at Washington University, St. Louis, Missouri, May 23-26, 1977. 17. Key Words (Suggested by Author(s)) 18. Distribution Statement Planetary geology Solar system evolution Unclassified—Unlimited Planetary geological mapping Instrument development 19. Security Qassif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price* Unclassified Unclassified 294 $9.25 * For sale by the National Technical Information Service, Springfield, Virginia 22161 FOREWORD This is a compilation of abstracts of reports from Principal Investigators of NASA's Office of Space Science, Division of Lunar and Planetary Programs Planetary Geology Program.
    [Show full text]
  • Searching for Crystal-Ice Domains in Amorphous Ices
    PHYSICAL REVIEW MATERIALS 2, 075601 (2018) Searching for crystal-ice domains in amorphous ices Fausto Martelli,1,2,* Nicolas Giovambattista,3,4 Salvatore Torquato,2 and Roberto Car2 1IBM Research, Hartree Centre, Daresbury WA4 4AD, United Kingdom 2Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA 3Department of Physics, Brooklyn College of the City University of New York, Brooklyn, New York 11210, USA 4The Graduate Center of the City University of New York, New York, New York 10016, USA (Received 7 May 2018; published 2 July 2018) Weemploy classical molecular dynamics simulations to investigate the molecular-level structure of water during the isothermal compression of hexagonal ice (Ih) and low-density amorphous (LDA) ice at low temperatures. In both cases, the system transforms to high-density amorphous ice (HDA) via a first-order-like phase transition. We employ a sensitive local order metric (LOM) [F. Martelli et al., Phys. Rev. B 97, 064105 (2018)] that can discriminate among different crystalline and noncrystalline ice structures and is based on the positions of the oxygen atoms in the first- and/or second-hydration shell. Our results confirm that LDA and HDA are indeed amorphous, i.e., they lack polydispersed ice domains. Interestingly, HDA contains a small number of domains that are reminiscent of the unit cell of ice IV,although the hydrogen-bond network (HBN) of these domains differs from the HBN of ice IV. The presence of ice-IV-like domains provides some support to the hypothesis that HDA could be the result of a detour on the HBN rearrangement along the Ih-to-ice-IV pressure-induced transformation.
    [Show full text]
  • 11Th International Conference on the Physics and Chemistry of Ice, PCI
    11th International Conference on the Physics and Chemistry of Ice (PCI-2006) Bremerhaven, Germany, 23-28 July 2006 Abstracts _______________________________________________ Edited by Frank Wilhelms and Werner F. Kuhs Ber. Polarforsch. Meeresforsch. 549 (2007) ISSN 1618-3193 Frank Wilhelms, Alfred-Wegener-Institut für Polar- und Meeresforschung, Columbusstrasse, D-27568 Bremerhaven, Germany Werner F. Kuhs, Universität Göttingen, GZG, Abt. Kristallographie Goldschmidtstr. 1, D-37077 Göttingen, Germany Preface The 11th International Conference on the Physics and Chemistry of Ice (PCI- 2006) took place in Bremerhaven, Germany, 23-28 July 2006. It was jointly organized by the University of Göttingen and the Alfred-Wegener-Institute (AWI), the main German institution for polar research. The attendance was higher than ever with 157 scientists from 20 nations highlighting the ever increasing interest in the various frozen forms of water. As the preceding conferences PCI-2006 was organized under the auspices of an International Scientific Committee. This committee was led for many years by John W. Glen and is chaired since 2002 by Stephen H. Kirby. Professor John W. Glen was honoured during PCI-2006 for his seminal contributions to the field of ice physics and his four decades of dedicated leadership of the International Conferences on the Physics and Chemistry of Ice. The members of the International Scientific Committee preparing PCI-2006 were J.Paul Devlin, John W. Glen, Takeo Hondoh, Stephen H. Kirby, Werner F. Kuhs, Norikazu Maeno, Victor F. Petrenko, Patricia L.M. Plummer, and John S. Tse; the final program was the responsibility of Werner F. Kuhs. The oral presentations were given in the premises of the Deutsches Schiffahrtsmuseum (DSM) a few meters away from the Alfred-Wegener-Institute.
    [Show full text]
  • Ice Molecular Model Kit © Copyright 2015 Ryler Enterprises, Inc
    Super Models Ice Molecular Model Kit © Copyright 2015 Ryler Enterprises, Inc. Recommended for ages 10-adult ! Caution: Atom centers and vinyl tubing are a choking hazard. Do not eat or chew model parts. Kit Contents: 50 red 4-peg oxygen atom centers (2 spares) 100 white hydrogen 2-peg atom centers (2 spares) 74 clear, .87”hydrogen bonds (2 spares) 100 white, .87” covalent bonds (2 spares) Related Kits Available: Chemistry of Water Phone: 806-438-6865 E-mail: [email protected] Website: www.rylerenterprises.com Address: 5701 1st Street, Lubbock, TX 79416 The contents of this instruction manual may be reprinted for personal use only. Any and all of the material in this PDF is the sole property of Ryler Enterprises, Inc. Permission to reprint any or all of the contents of this manual for resale must be submitted to Ryler Enterprises, Inc. General Information Ice, of course, ordinarily refers to water in the solid phase. In the terminology of astronomy, an ice can be the solid form of any element or compound which is usually a liquid or gas. This kit is designed to investigate the structure of ice formed by water. Fig. 1 Two water molecules bonded by a hydrogen bond. Water ice is very common throughout the universe. According to NASA, within our solar system ice is The symbol δ means partial, so when a plus sign is found in comets, asteroids, and several moons of added, the combination means partial positive the outer planets, and it has been located in charge. The opposite obtains when a negative sign interstellar space as well.
    [Show full text]
  • Mechanical Characterization Via Full Atomistic Simulation: Applications to Nanocrystallized Ice
    Mechanical Characterization via Full Atomistic Simulation: Applications to Nanocrystallized Ice A thesis presented By Arvand M.H. Navabi to The Department of Civil and Environmental Engineering in partial fulfillment of the requirements for the degree of Master of Science in the field of Civil Engineering Northeastern University Boston, Massachusetts August, 2016 Submitted to Prof. Steven W. Cranford Acknowledgements I acknowledge generous support from my thesis advisor Dr. Steven W. Cranford whose encouragement and availability was crucial to this thesis and also my parents for allowing me to realize my own potential. The simulations were made possible by LAMMPS open source program. Visualization has been carried out using the VMD visualization package. 3 Abstract This work employs molecular dynamic (MD) approaches to characterize the mechanical properties of nanocrystalline materials via a full atomistic simulation using the ab initio derived ReaxFF potential. Herein, we demonstrate methods to efficiently simulate key mechanical properties (ultimate strength, stiffness, etc.) in a timely and computationally inexpensive manner. As an illustrative example, the work implements the described methodology to perform full atomistic simulation on ice as a material platform, which — due to its complex behavior and phase transitions upon pressure, heat exchange, energy transfer etc. — has long been avoided or it has been unsuccessful to ascertain its mechanical properties from a molecular perspective. This study will in detail explain full atomistic MD methods and the particulars required to correctly simulate crystalline material systems. Tools such as the ReaxFF potential and open-source software package LAMMPS will be described alongside their fundamental theories and suggested input methods to simulate further materials, encompassing both periodic and finite crystalline models.
    [Show full text]
  • Formation of Clathrate Hydrate from Amorphous Ice During Warming R
    Formation of clathrate hydrate from amorphous ice during warming R. Netsu, T. Ikeda-Fukazawa Department of Applied Chemistry, Meiji University, Japan Water molecules are condensed on dust grains in interstellar molecular clouds and protester nebulae. The water exists as amorphous ice in the cold clouds and is transformed into various structures depending on thermal conditions and compositions with various deposited molecules. Blake et al. [1] proposed the presence of CO2 clathrate hydrate in cometary ice. From the results using the transmission electron microscopy (TEM) and fourier transformed infrared spectroscopy (FT-IR), they showed the phase transition of vapor deposited amorphous ice including CO2 and CH3OH into type-II clathrate hydrate at around 120 K. Clathrate hydrates are inclusion compounds consisting of water molecules and a variety of guests molecules. Most clathrate hydrates form one of two distinct crystallographic structures, type-I and –II, depending on the sizes and shapes of the guest molecules. The cubic unit cell of type-I clathrate hydrate contains 46 water molecules in a framework of two dodecahedral and six tetrakaidecahedral cages, and that of type-II clathrate hydrate contains 136 water molecules in a framework of 16 dodecahedral and eight hexakaidecahedral cages. The structure of CO2 clathrate hydrate formed under a high pressure condition is type-I [2]. For the hydrate from the vapor deposited amorphous ice [1], the structure is type-II due to the help-gasses effect of CH3OH. For the CO2 clathrate hydrate grown epitaxially on a hydrate in low pressure conditions, the structure depends on the structure of the hydrate as the substrate [3].
    [Show full text]
  • Spectroscopic Signatures of Halogens in Clathrate Hydrate Cages. 1
    13792 J. Phys. Chem. A 2006, 110, 13792-13798 Spectroscopic Signatures of Halogens in Clathrate Hydrate Cages. 1. Bromine Galina Kerenskaya,* Ilya U. Goldschleger, V. Ara Apkarian, and Kenneth C. Janda Department of Chemistry, UniVersity of California IrVine, IrVine, California 92697 ReceiVed: July 17, 2006; In Final Form: October 19, 2006 We report the first UV-vis spectroscopic study of bromine molecules confined in clathrate hydrate cages. Bromine in its natural hydrate occupies 51262 and 51263 lattice cavities. Bromine also can be encapsulated into the larger 51264 cages of a type II hydrate formed mainly from tetrahydrofuran or dichloromethane and water. The visible spectra of the enclathrated halogen molecule retain the spectral envelope of the gas-phase spectra while shifting to the blue. In contrast, spectra of bromine in liquid water or amorphous ice are broadened and significantly more blue-shifted. The absorption bands shift by about 360 cm-1 for bromine in large 51264 cages of type II clathrate, by about 900 cm-1 for bromine in a combination of 51262 and 51263 cages of pure bromine hydrate, and by more than 1700 cm-1 for bromine in liquid water or amorphous ice. The dramatic shift and broadening in water and ice is due to the strong interaction of the water lone-pair orbitals with the halogen σ* orbital. In the clathrate hydrates, the oxygen lone-pair orbitals are all involved in the hydrogen- bonded water lattice and are thus unavailable to interact with the halogen guest molecule. The blue shifts observed in the clathrate hydrate cages are related to the spatial constraints on the halogen excited states by the cage walls.
    [Show full text]
  • Astrophysics of Life Conference Highlights
    AstrobiologyAstrobiology 740740 FollowFollow thethe IceIce JanuaryJanuary 13,13, 20062006 Dr. Karen J. Meech, Astronomer Institute for Astronomy, Univ. Hawaii [email protected]; (808) 956-6828 MoonMoon--MarsMars InitiativeInitiative z Implement sustained human / robotic exploration of the solar system and beyond; z Extend human presence across the solar system, z Human return to the Moon by 2020, z Preparation for human exploration of Mars & beyond z Search for evidence of life z Develop the necessary innovative technologies, knowledge, and infrastructures z Conduct advanced telescopic searches for Earth-like planets and habitable environments around other stars z Promote international and commercial participa- tion in exploration WeWe areare AqueousAqueous BeingsBeings…….. z Water is the medium for life’s chemistry z Our cells are mostly water z Water is a liquid for large ∆T z Water ice floats z Water affects Earth’s energy budget z Water involved in geochemical reactions Æ atm chemical balance z Water in Earth’s mantle affects internal melting behavior HabitableHabitable ZonesZones DependsDepends onon z Planet properties: albedo, atmospheric density & composition, rotation Distance from the central star where the equilibrium T allows z Age of star – luminosity where the equilibrium T allows for the existence of liquid water increases with time z Planetary orbit z Internal heat sources OurOur SolarSolar SystemSystem Planet Albedo Radius Distance Eccen TBB Mercury 0.119 2439 0.3871 0.206 445 Venus 0.750 6052 0.7233 0.007 238 Earth
    [Show full text]
  • Bruno Escribano Basque Center for Applied Mathematics Julyan Cartwright CSIC - University of Granada Outline
    Spring-block tessellations with n springs per block Bruno Escribano Basque Center for Applied Mathematics Julyan Cartwright CSIC - University of Granada Outline • 1. Motivation • 2. Introduction: – spring tessellations (tilings) – crystals, quasicrystals and amorphous solids • 3. Results • 4. Conclusions and outlook Motivation: types of Ice crystalline Ice on Earth hexagonal (snow, glaciers, icebergs…) Amorphous ice Ice in the Universe and others… ??? Motivation: ice in the Universe • Interstellar dust grains, asteroids, comets, surface of planets and moons… • Formed at very low temperatures • Unknown morphology • Unknown structure Phase transition? • Different amorphous ices depending on the deposition temperature. 130 K > Tm > 30 K → Low Density Amorphous (LDA) 30 K > Tm → High Density Amorphous (HDA) Possible phase transition HDA → LDA ? ESEM Setup Environmental SEM Microscope + liquid He circuit. In low vacuum at temperatures 6-220 K Grow ice in-situ injecting water vapor. Mesoscopic morphologies HDA T=6 K LDA T=77 K Hexagonal T=250 K We still don't know about the molecular structure! Characterizing amorphous solids X-ray / neutron diffraction Radial distribution functions Jenniskens et al. APJ (1995) Finney et el. Phys. Rev. Lett. (2002). What kind of structure would produce these results? 2D tessellations 3 regular tessellations 8 semiregular tessellations Pentagonal tessellations 14 known pentagonal tessellations: Beyond periodicity: quasicrystals Penrose tilings (1976) • Ordered but not periodic (no translational symmetry). • Defined by quasiperiodic functions. i.e. f(x)=cos(x)+cos(αx) where α is irrational Can this happen naturally? Beyond periodicity: quasicrystals Shechtman et al. (1984) AlCuFe icosahedral phase Beyond periodicity: quasicrystals “Crystal is any solid which possesses an essentially discrete diffraction pattern.” International Crystallographic Union, 1991 Crystalline Amorphous So we now define crystals (and quasicrystals) through an experimental technique, but..
    [Show full text]