New state of water molecule discovered

The behavior of water molecules under severe confinement has been discovered by neutron scattering and computer modeling to be distinct and surprising, unlike any known gas, liquid, or solid state.

Researchers at Oak Ridge National Laboratory, part of the Department of Energy, have described a novel tunneling state of water molecules trapped in hexagonal ultra-small channels of the mineral beryl, which are 5 angstroms wide, in an article that was published in Physical Review Letters. A single atom's diameter is usually around one angstrom, and one angstrom is equal to 1/10-billionth of a meter.

The findings, which illustrate characteristics of water under ultra confinement in rocks, soil, and cell walls, were made possible by research at ORNL's Spallation Neutron Source and the Rutherford Appleton Laboratory in the United Kingdom. Scientists anticipate that these findings will be of interest to a wide range of fields.

Lead author Alexander Kolesnikov of ORNL's Chemical and Engineering Materials Division stated, "At low temperatures, this tunneling water exhibits quantum motion through the separating potential walls, which is forbidden in the classical world." This indicates that the water molecule's oxygen and hydrogen atoms are "delocalized," meaning they are concurrently present in each of the channel's six symmetrically equivalent locations at the same time. It is one of those rare occurrences in quantum physics that is unmatched in the real world."

It should be easier for scientists to describe the thermodynamic characteristics and behavior of water in highly confined environments, such as water diffusion and transport in cell membrane channels, carbon nanotubes, along grain boundaries, and at mineral interfaces in a variety of geological environments, now that the tunneling state of water has been demonstrated by ORNL's study.

Co-author Lawrence Anovitz of ORNL observed that as scientists work to understand how their materials are affected by this event and figure out its mechanism, conversations involving materials, biological, geological, and computational scientists are likely to arise.

"This finding offers a fresh, fundamental understanding of how water behaves and uses energy," Anovitz stated. "It's also intriguing to consider that the blue and green beryl water molecules in your aquamarine or emerald ring are experiencing the same quantum tunneling that we've observed in our experiments."

Although atomic hydrogen has been shown to tunnel in other systems in earlier research, the ORNL finding that water demonstrates this kind of tunneling behavior is novel. The results of the computational chemistry and neutron scattering studies demonstrated that the water molecules take on a unique double top-like structure when they are delocalized around a ring in the tunneling state.

"It is approximately thirty percent less than it is in bulk liquid or solid water," Kolesnikov stated. "The average kinetic energy of the water protons directly obtained from the neutron experiment is a measure of their motion at almost absolute zero temperature." "Based on the energies of its vibrational modes, this is completely at odds with accepted models."

Narayani Choudhury of Lake Washington Institute of Technology and University of Washington-Bothell shown via first-principles simulations that the tunneling behavior is connected to the vibrational dynamics of the beryl structure.

The authors of the publication, "Quantum Tunneling of Water in Beryl: a New State of the Water Molecule," were Andrew Seel of Rutherford Appleton Laboratory, George Reiter of the University of Houston, Timothy Prisk, Eugene Mamontov, Andrey Podlesnyak, George Ehlers, and David Wesolowski from ORNL. An grant from DOE's Office of Basic Energy Sciences supported this study. The SNS is a user facility of the DOE Office of Science.