Water Molecule

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Introduction

Intro paragraph

Plan

• Introduction

  • Atomic structure

• Summary

Page

• Status:

• Reviewed: ❌

• Updated: 04/02/2023

Notes

To Do

• Think about coherent plan

• Implement

Colaboration

Star formation is not my expertise so if you want to help, feel free to comment the contribution you could make

Introduction

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

Molecular Structure

Atomic Orbitals

Note

Table about the different quantum numbers

Fig. 4 Source

Fig. 5 Source

Fig. 6 Source

Fig. 7 Source

‣ Properties

‣ ‣ Anomalous macroscopic behaviour

Water molecules are symetric (point group C_2V - two mirror planes of symmetry and a 2-fold rotation axis).

• Is it important ?

writing ✏

Geometry,

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

• Article to download

• Article to download

• OK, why bother ?

• Other articles

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 ^^^

• ν₁: symmmetric stretch, 3657 cm^-1

Asymetric ^^^

• ν₃: asymmetric stretch, 3756 cm^-1

Bending ^^^

• ν₂: bending, 1595 cm^-1

Isotopologues

Litterature

rotational-vibrational spectra of water vapor

• H₂¹⁷O and H₂¹⁸O
  [Tennyson et al., 2009]

• HD¹⁶O, HD¹⁷O and HD¹⁸O
  [Tennyson et al., 2010]

• D₂¹⁶O, D₂¹⁷O and D₂¹⁸O
  [Tennyson et al., 2014]

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).

Fig. 8 source: [Novak, 1973]

Different types of Hydrogen bonds ?

• linear

• bifurcated

  • [Giguere, 1984]

  • [A and A, 1987]

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

Fig. 9 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

Fig. 10 Source: link - to redo black: OH of interest red:intramolecular coupling blue: strong intermolecular coupling green: weak 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** ?

• Two-dimensional Raman spectroscopy (?) - [Saito and Ohmine, 2006]