Water, its Structure and its Isotopologues.

WATER (H2O) is the third most common molecule in the Universe (after H2 and CO), the most abundant substance on earth and the only naturally occurring inorganic liquid, a billion cubic kilometers of which reside in our oceans and 50 tons of which pass through our bodies in our lifetimes. It has been very well studied with a number of model structures having been proposed and refined. Notwithstanding this, extensively hydrogen-bonded liquid water is unique with a number of anomalous properties. It has commonly been stated that no single model is able to explain all of its properties.

And we all thought water was the simplest of all things. Evidently not. Let's have a closer look at it.

The first complication with water is that there are three different forms of hydrogen that we know of, each capable of combining with oxygen to produce a clear odourless liquid that on first inspection looks and feels like water.

The first, protium (H), is the one we commonly associate with hydrogen. It has at its core only one proton.

The second, deuterium (D), has one proton and one neutron at its core. In combination with oxygen it becomes D2H, which is known as heavy water. Deuterium occurs in water at about 0.015%.

The third, tritium (T), has one proton and two neutrons at its core. It is radioactive and has a half life of 12.32 years. It combines with oxygen to form tritiated water T2O. The low-energy beta radiation from tritium cannot penetrate human skin, so tritium is only dangerous if inhaled or ingested.

The three forms of hydrogen combine with water to form what we know as water and five isotopologues. (The isotopologue of a chemical species has at least one atom with a different number of neutrons.) This gives as the only possible combinations , all of which occur in what we call water:

H-O-H , D-O-H , T-O-H , D-O-D , T-O-D , T-O-T

This is not where the complexity stops.

The following are a few selected facts from available literature:

The water molecule may vibrate in a number of ways. In the gas state, the vibrations involve combinations of symmetric stretch (v1), asymmetric stretch (v3) and bending (v2) of the covalent bonds.

Main vibrations of water isotopologues
v1, cm-1
v2, cm-1
v3, cm-1

The main stretching band in liquid water is shifted to a lower frequency (v3, 3490 cm-1 and v1, 3280 cm-1)
and the bending frequency increased (v2, 1644 cm-1) by hydrogen bonding.

Main vibrations of liquid ordinary and heavy water
liquid H2O (25C)
liquid D2O (25C)
v, cm-1
E0, M-1 cm-1
v, cm-1
E0, M-1 cm-1
v2+ libration
v1+v3+v2 (overtone)

This is what the vibratory movement looks like.

It is clear that life on Earth depends on the unusual structure and anomalous nature of liquid water. Organisms consist mostly of liquid water. This water performs many functions and it can never be considered simply as an inert diluent; it transports, lubricates, reacts, stabilizes, signals, structures and partitions. The living world should be thought of as an equal partnership between the biological molecules and water. In spite of much work, many of the properties of water are puzzling. Enlightenment comes from an understanding that water molecules form an infinite hydrogen-bonded network with localized and structured clustering. The middling strength of the connecting hydrogen bonds seems ideally suited to life processes, being easily formed but not too difficult to break. An important concept, often overlooked, is that liquid water is not homogeneous at the nanoscopic level.

There is obviously much more to it, but this is what it boils down to.

Water is not H-O-H, this is only a way of talking. True, for most purposes the formula holds, but it is only true for the average body of water over a longish period of time.

The hydrogen atoms in water are not rigidly fixed to the oxygen atoms and have a tendency to move around and find new oxygen partners. A bit like our modern society perhaps?

Even in true H2O molecules there are at least three distinct modes of vibration that have different frequencies.

Water has a tendency to form clusters.

Water has memory. Water can remember a structure it was forced to assume by being made to regroup in the presence of some foreign substance long after that foreign substance disappeared. (According to some scientists this explains the workability of homeopathy.)

There are sixty three known anomalities of water. To go into this subject here exceeds the scope of this paper. Suffice it to say we are dealing with a complex substance that has a life of its own and often behaves in ways difficult to forecast.

Therefore the dissociation of water with a vibratory stream is not an easy task and should not be undertaken lightly without reasonable safeguards especially as to explosions.

Next Chapter:


Hans von Lieven, copyright 2007