Water also has unusually high surface tension, which enables insects to walk on its surface, and also has huge heat storage capacity, which keeps the ocean at a stable temperature.
Now, for the first time, a group of researchers from SLAC National Accelerator Laboratory of the US Department of Energy, Stanford University and Stockholm University in Sweden have directly observed how hydrogen atoms in water molecules push and pull neighboring water molecules when excited by laser. Their findings were published in the journal Nature on August 25th, local time. This study reveals the influence of key aspects that may support the micro-origin of water's strange properties, and may give people a better understanding of how water helps protein to play a role in organisms.
"Although this so-called nuclear quantum effect is assumed to be the core of many strange properties of water, this experiment marks the first time that it has been directly observed," said Anders Nilsson, a co-author of the study and a professor of chemical physics at Stockholm University. "The question is whether this quantum effect may be a missing link in the theoretical model describing the abnormal properties of water."
Each water molecule contains one oxygen atom and two hydrogen atoms, and the hydrogen bond network between the positively charged hydrogen atom in one molecule and the negatively charged oxygen atom in the adjacent molecule connects them together. This complex network is the driving force behind many puzzling characteristics of water, but until recently, researchers could not directly observe how water molecules interact with their neighbors.
"The low mass of hydrogen atoms highlights their quantum wave behavior," said Kelly gaffney, a partner and scientist at SLAC Stanford Pulse Institute. "This study directly proves for the first time that the response of hydrogen bond networks to energy pulses depends on the quantum mechanical properties of hydrogen atom spacing. For a long time, it has been considered to be the reason for the unique properties of water and its hydrogen bond network. "
So far, it has been a challenge to make such observation, because the movement of hydrogen bonds is so tiny and fast. However, this experiment now uses MeV-UED of SLAC to overcome this problem. MeV-UED is a high-speed "electronic camera", which detects the fine motion of molecules by scattering powerful electron beams to samples.
The research team made a liquid water jet with a thickness of 100 nanometer-about 1000 times the width of human hair-and used infrared laser to make water molecules vibrate. Then, they bombarded these molecules with short pulses of high-energy electrons generated by MeV-UED.
This produces a high-resolution snapshot of the structural changes of molecules and atoms, which are strung together to form a stop-motion animated film, showing the reaction of water molecule networks to light.
These snapshots focus on a group of three water molecules, revealing that when an excited water molecule starts to vibrate, the hydrogen atom pulls the oxygen atoms in the adjacent water molecules closer, and then pushes them away with the newly discovered force to expand the space between molecules.
"For a long time, researchers have been trying to use spectroscopy to understand hydrogen bond networks," said Yang Jie, a former SLAC scientist and now a professor at Tsinghua University. "The beauty of this experiment is that for the first time, we can directly observe how these molecules move."
Researchers hope to use this method to deeply understand the quantum properties of hydrogen bonds and their role in the strange properties of water, as well as the key roles these properties play in many chemical and biological processes.
"This really opens a new window for water research," said Xijie Wang, a scientist and paper research collaborator at SLAC. "Now we can finally see the movement of hydrogen bonds, and we hope to connect these movements with a broader picture, which may clarify how water leads to the origin and survival of life on earth and provide information for the development of renewable energy methods."