There is a storm in the cup of nice tea that we barely understand. Water molecules go crazy around, spread to each other, grab and let go in unique ways that challenge easy study.
While physicists know that the hydrogen bonding phenomenon plays a key role in the strange and wonderful configurations of water, certain details of how exactly it works have been quite vague.
An international team of researchers adopted a new approach to imagining the positions of particles that make up liquid water, capturing the blur accurately in femtoseconds to reveal how hydrogen and oxygen sink into water molecules.
Their results may not help us get a better cup of tea, but they do contribute a lot to the quantum modeling of hydrogen bonds, potentially improving theories that explain why water is so vital to life. as we know it, it has such interesting properties.
“This has opened a new window for studying water,” says Xijie Wang, a physicist at the U.S. Department of Energy’s SLAC National Accelerator Laboratory.
“Now that we can finally see how the hydrogen bonds move, we would like to connect these movements with a broader picture, which could shed light on how water led to the origin and survival of life on Earth. and report on the development of renewable energy methods. “
In isolation, a single molecule of water is a three-way custody battle over electrons between two hydrogen atoms and a single oxygen atom.
With far more protons than its pair of weenie companions, oxygen gets a little more out of the molecule’s electronic love. This makes each hydrogen have a little more electron free time than usual. The tiny atoms are not exactly positively charged, but they do become a V-shaped molecule with a smooth slope of subtly positive tips and a slightly negative nucleus.
Throw several of these molecules together with enough energy, and the small charge variations will be arranged accordingly, with the same charges separated and unlike the charges that bind.
While all of this may seem simple enough, the engine behind this process is anything but straightforward. Electrons zoom approximately under the influence of various quantum laws, that is, the closer we look, the less certain we can have about certain properties.
Previously, physicists had relied on ultrafast spectroscopy to understand how electrons move in the chaotic tug-of-war of water, capturing photons of light and analyzing their signature to map the positions of electrons. .
Unfortunately, this leaves out a crucial part of the landscape: the atoms themselves. Far from passive spectators, they also flex and oscillate with respect to quantum forces moving around them.
“The low mass of hydrogen atoms accentuates their wave-like quantum behavior,” says SLAC physicist Kelly Gaffney.
To obtain information about the arrangements of the atom, the team used something called Megaelectronvolt Ultrafast Electronic Diffraction Instrument, or MeV-UED. This device from the national accelerator laboratory of the SLAC coats water with electrons, which carry crucial information about the arrangement of atoms as they leave the molecules.
(Greg Stewart / SLAC National Accelerator Laboratory)
At the top: The animation shows how a water molecule responds after being hit with laser light. When the excited water molecule begins to vibrate, its hydrogen atoms (white) drag the oxygen atoms (red) from the nearest water molecules closer, before moving them away, expanding the space between molecules.
With enough snapshots, it was possible to create a high-resolution image of the hydrogen jiggle as the molecules bent and flexed around it, revealing how they drag oxygen from neighboring molecules toward them before returning. to push them violently.
“This study is the first to directly demonstrate that the response of the hydrogen bond network to an energy impulse critically depends on the quantum mechanical nature of how hydrogen atoms separate, which it has long been suggested that it is responsible for the unique attributes of water and its network of hydrogen bonds, ”says Gaffney.
Now that the tool has been shown to work in principle, researchers can use it to study the turbulent waltz of water molecules as pressures rise and temperatures drop, observing how it responds to the organic solutes that create water. life or form amazing new phases in exotic conditions.
Never before has a storm looked so elegant.
This research was published in Nature.