For The First Time, Physicists Observed a Quantum Property That Makes Water Weird

A storm is brewing in your teacup, with a variety of phenomena we don't understand. Water molecules are fumbling about like mad, reaching out to each other, grasping hold, and letting go in ways that defy simple study.
Although scientists know that hydrogen bonding is a major factor in water's bizarre and wonderful configurations of molecules, details about how it works are still largely unknown.

A team of international researchers devised a new method to image the positions of water particles. They captured their blurred images with femtosecond precision, to show how hydrogen and oxygen interact within water molecules.

Although their results may not make us drink better tea, they help to clarify the quantum modeling of hydrogen bonds. This could lead to improved theories about why water is so essential for our lives.

"This has really opened a window to study water," said Xijie Zhang, a physicist at the US Department of Energy’s SLAC National Accelerator Laboratory.

"Now that we see hydrogen bonds moving, it's time to link those movements with the larger picture. This could shed light on water's role in the origin and survival on Earth, and help us develop renewable energy methods.

A single molecule of water can be considered an isolated atom. This means that it is subject to a three-way custody battle for electrons. It must compete with two hydrogen atoms or one oxygen.

Oxygen gets a little more electron love from its protons than its weenie sidekicks. Each hydrogen has a little less electron-free time. Although the tiny atoms don't get left positively charged, it makes for a V-shaped molecular structure with subtly positive tips at the edges and a slightly negative center.

With enough energy, you can mix a few of these molecules together and see small differences in charge. Similar charges push apart, unlike charges come together.

Although it may sound easy, the actual engine of this process is complex. The influence of quantum laws causes electrons to zoom around under various quantum laws. This means that the closer we look the less certain certain properties are.

To understand the movement of electrons in water's chaotic tug of war, physicists used ultrafast spectroscopy. They caught photons of light, and then analysed their signatures to map the electron positions.

This leaves out an important part of the scene: the atoms. They are not passive observers, but they also move and flex in response to the quantum forces around them.

Kelly Gaffney, SLAC physicist, says that the low mass of hydrogen atoms accentuates its quantum wave-like behavior.

The team used a Megaelectronvolt Ultrafast Effraction Instrument (MeV-UED) to gain insight into the arrangement of the atoms. The National Accelerator Laboratory at SLAC showers water with electrons. These electrons carry important information about the atoms' arrangement as they ricochet off the molecules.

(Greg Stewart/SLAC National Accelerator Laboratory

Above: Animation of how water molecules react to laser light. The excited water molecule vibrates and its hydrogen atoms, (white), pull oxygen atoms from nearby water molecules closer before pushing them away. This expands the space between the molecules.

It was possible to take enough photos to get a high-resolution image of the jiggle and movement of hydrogen molecules as they bend and stretch around them. This revealed how they pull oxygen from nearby molecules towards them before pushing them back.

Gaffney says, "This study is the only to show that the reaction of the hydrogen bond networks to an energy impulse depends on the quantum mechanical nature how the hydrogen atoms spaced out. This has been long suspected to be responsible for water's unique characteristics and hydrogen bond network."

The tool is now in principle demonstrated to work. Researchers can now use it to study water molecules' turbulent movements as temperatures rise and fall. They can also observe how the water reacts to organic solutes that are vital to life or form new phases under unusual conditions.

Never did a storm look quite so graceful.

The research was published by Nature.