Water Ice#

We are all familiar with water. Even though water is a relatively simple molecule, the third most abundant molecule in the Universe (after H2 and CO), and the most abundant molecule on Earth it not yet and far from being completely understood.

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Some general comments about water

  • Why we are interested in it

Plan

  • Introduction

    • Water molecule

      • Vibrational modes

    • Phase diagram



  • Water in the condensed phase

    • Moledular interaction

      • Hydrogen bonds

    • Crystalisation



  • The solid landscape

    • Hexagonal Ice

      • Crystal structure



  • Amorphous Ice

    • Amorphous vs crystaline ice

Key Litterature:



Links

Teaching ✏️

Water

Water_moleucule

Link:


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Water molecule#

Water is … very important:

  • Solar radiation absorbed by the Earth atmosphere is mostly due to water vapour absorption. []

  • Key molecule for life …

It is commonly stated that the presence of liquid water is a necessary condition for the appearance of life:

  • Hydratation properties for biological macromolecules

    • determine their 3D structures and biological functions in solutions (sol-gel phase transition ?)

  • …

Water is more than just a solvent

» Properties

Anomalous macroscopic behaviour

Water molecules are symetric (point group C2V - two mirror planes of symmetry and a 2-fold rotation axis).

  • Is it important ?

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Geometry,

H atoms could have paralell or antiparallel nuclear spin (orto vs para)

Microscopic properties

Polarity, Dipole moment and Vibrational modes

Polarity makes water an excellent solvent

The dipole moment of a free water molecule is 1.86 D (Debye) [Aida and Akase, 2019] (ref 22) - [Akase and Aida, 2014]

  • How is it measured, calculated

Monomer band assignment from [Tennyson et al., 2013]

Symetric ^^^

sym stretch

  • ν1: symmmetric stretch, 3657 cm-1

Asymetric ^^^

sym stretch

  • ν3: asymmetric stretch, 3756 cm-1

Bending ^^^

sym stretch

  • ν2: bending, 1595 cm-1

Isotopologues

Isotopologues are a great investigation tool to unveil the various processes that a molecular species has had to overcome over it’s existence.

Hydrogen bonding

Definition

The hydrogen bond is an attractive interaction between a hydrogen atom from a molecule or a molecular fragment X–H in which X is more electronegative than H, and an atom or a group of atoms in the same or a different molecule, in which there is evidence of bond formation.

—IUPAC definition, 2011 (to cite)

Hydrogen bonds are the most important stabilizing interaction in nature, playing a key role in the structure of proteins and DNA. First described by Linus Pauling in a letter to William Bragg in 1929.

  • copy pasted (rewrite)

The potential energy function of the free AH group is thus modified by the potential B; it becomes broader and the vibrational levels become closer as reflected by the shift of the AH stretching band toward lower frequencies shown by infrared and Raman spectroscopy. At the same time, the proton of the AH group shifts toward B and the equilibrium r (A–H) distance increases while the intermolecular R (A.. B) distance decreases to a value less than the sum of the Van der Waals radii of the A and B atoms. The geometrical changes have been detected by neutron and X-ray diffraction methods (1–4).

../../_images/Novak_potential.PNG

Fig. 5 source: [Novak, 1973]#

Different types of Hydrogen bonds ?
Molecular interaction
Geometry

Best way to study intermolecular interaction is in the solid phase, at low temerature (reduce molecular movement ….)

The basic principles that govern the arrangement of atoms in water ice are called the ice rules (or Bernal–Fowler rules) and they state that each oxygen is covalently bonded to two hydrogen atoms and that the oxygen atom in each water molecule forms two hydrogen bonds with other water molecules. As a result, each water molecule is embeded in a teraedron formed by four neighbouring molecules, called a Walrafen pentamer

../../_images/Walf_tetra_MC.PNG

Fig. 6 Explain: source MC#

This tetrahedral geometry is caused by the ability of water to form 4 hydrogen bonds with other water molecules:

  • 2 donors (D) from the 2 hydrogens

  • 2 acceptors (A) from the Oxygen lone pairs of electrons

Different forms of Hydrogen bonds

Van der Walls interaction / distances

Proton order/disorder ?

Intermolecular coupling

  • Strong / Weak

  • Effect on the IR vibrations

Note

Does it strenghten, weaken the bonds?

» Investigation techniques

One of the major issue in obtaining a consensus about water structure is the broad range of technique that are used to investigate it’s properties.

Structure

Methods

Time and size scales

Instantaneous

X-ray absorption

10-15 s, single molecule

Almost instantaneous

Infrared, Raman

10-14 - 10-13 s, single molecule - local cluster

Vibrationally averaged

Models, Pump-probe laser

10-12 - 10-12 s, single molecule - local cluster

Diffusionally averaged

Neutron scattering, NMR shift

10-9 - 10-6 s, local cluster

Probability

X-ray diffraction, thermodynamics

> s, local cluster

Infrared spectroscopy

  • Compatible with astronomical observations (cf next chapter - link)

    • 3µ ice band

Note

orto vs para water - lsbcu

IR vs Raman

Note

What is the difference

Fermi Resonnances** ?

Water in the condensed phase#

» Phase diagram

The earth is the only planet of our solar system that can sustain water in it’s three physical states (solid, liquid, gas).

Liquid

  • supercooled liquid water

  • High density vs low density liquid

    • Scihub link - Structure and phase diagram of high-density water: The role of interstitial molecules - Molecular dynamics paper but interesting

../../_images/Phase_diagram_of_water.svg

Fig. 8 Explain: source MC#

../../_images/Phase_diagram_2.PNG

Fig. 9 Explain: source MC#

Phase diagram 2 source

Infrared Investigation

Note

IR Spectra of the different phases

Gas spectra
Absorption spectra of liquid and solid water

» Cluster

Water dimer

History Review

Influence on the IR bands

Cooperative Hydrogen Bonding

increase in dipole moment with the increase in hydrogen bonding coordination

Effect on the IR vibrations

Note

what these underlying absorption peaks represent?

The absorption bands also reflect coherent vibrational transfer involving several to many water molecules - [Yang and Skinner, 2010] (liquid water work)

Fitting method

OH stretch is big potato, sum of multiple subfeature (peaks)

Gaussian or Lorentzian ?

  • Voight profile ? (combination of both)

Other clusters

[Aida and Akase, 2019]

» Crystalisation

At molecular scales (few molecules up to 100 ?) - Matrix isolation techniques

Water_moleucule

Question

At what number of molecule do you consider a solid phase

The solid landscape#

Ice is Water frozen in the solid state.

» Hexagonal Ice

Hexagonal Ice (abbreviated Ih) is the most common form of ice found on earth

Crystal structure

lattice

Infrared Spectra

Raman

  • []

Molecular arrangements

  • Tetraedral

Unit cell parameters

» Water ice polymorphism

number of poymorphs, how do they differ

Cubic Ice

Stacking Disorder Ice

Amorphous Ice#

» Amorphous vs Crystaline Ice

Comparison

Crystaline

  • Polymorph: 18 ?

  • Ice rules

Amorphous

  • Polymorph: 5

Amorphous Solid Water