There's a storm brewing in your teacup that we can hardly comprehend. Water molecules are whirling around, reaching out to one another, grabbing hold and letting go in unusual ways that defy straightforward analysis.
While scientists understand that hydrogen bonding plays a significant part in water's many strange and fascinating forms, the specifics of how it works have remained a mystery.
An multinational team of researchers developed a novel method for visualising the locations of particles in liquid water, capturing their blur with femtosecond precision to illustrate how hydrogen and oxygen jiggle among water molecules.
Their findings may not help us make a better cup of tea, but they go a long way toward fleshing out quantum modelling of hydrogen bonding, perhaps improving theories explaining why water, which is so important to life as we know it, has such remarkable qualities.
"This has definitely opened up a new window to investigate water," says Xijie Wang, a physicist at the SLAC National Accelerator Laboratory of the US Department of Energy.
"Now that we can see the hydrogen bonds moving, we'd like to connect them to the bigger picture, which could throw light on how water contributed to the origin and survival of life on Earth, as well as inform the development of renewable energy methods."
A single molecule of water is a three-way custody war for electrons between two hydrogen atoms and a single oxygen atom when studied in isolation.
Oxygen receives significantly more electron love than its two weenie sidekicks since it has far more protons. This gives each proton a little more time without an electron than usual. Although the atoms aren't all positively charged, the result is a V-shaped molecule with a gentle slope of slightly positive tips and a slightly negative centre.
When enough energy is applied to a group of these molecules, the slight variances in charge will arrange themselves in the desired pattern, with same charges pushing apart and unlike charges merging together.
While this may appear to be a straightforward operation, the engine that drives it is anything but. Electrons move around according to numerous quantum principles, therefore the closer we get to them, the less certain we may be about their qualities.
Physicists had previously depended on ultrafast spectroscopy to learn how electrons travel in water's chaotic tug-of-war, collecting photons of light and analysing their signature to map electron positions.
Regrettably, this leaves out an important aspect of the scene: the atoms themselves. They stretch and wobble in response to the quantum forces changing around them, far from being passive onlookers.
"The low mass of hydrogen atoms emphasises their quantum wave-like activity," explains Kelly Gaffney of SLAC.
The team employed a Megaelectronvolt Ultrafast Electron Diffraction Instrument, or MeV-UED, to acquire insight into the atoms' configurations. This gadget at SLAC's National Accelerator Laboratory showers water with electrons, which ricochet from molecules and transmit important information about the atoms' configurations.
(Greg Stewart/SLAC National Accelerator Laboratory)
Above: An animation depicting the reaction of a water molecule to laser light. When an excited water molecule vibrates, its hydrogen atoms (white) pull oxygen atoms (red) from nearby water molecules closer before pushing them away, enlarging the distance between them.
With enough images, a high-resolution image of hydrogen jitter as the molecules bend and flex around them might be built, demonstrating how surrounding molecules drag oxygen towards them before forcefully flinging it back.
"This is the first study to show that the response of the hydrogen bond network to an energy impulse is critically dependent on the quantum mechanical nature of how the hydrogen atoms are spaced out, which has long been thought to be responsible for the unique properties of water and its hydrogen bond network," Gaffney says.
Researchers may now use the technique to investigate the tumultuous waltz of water molecules as pressures increase and temperatures fall, monitoring how it responds to life-building organic solutes or produces fascinating new phases under extreme conditions now that the tool has been proven to work in principle.
Never before had a storm appeared to be so lovely.
This study was published in the journal Nature.
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