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.
Provided by
Oak Ridge National Laboratory
