reactive state
It's the first direct observation of a hydroxyl-hydronium complex -
important for a wide range of chemical and biological processes from the tails of comets to cancer treatment

Date:
October 2, 2021
Source:
DOE/SLAC National Accelerator Laboratory
Summary:
Researchers have uncovered a key step in the ionization of liquid
water using the lab's high-speed 'electron camera,' MeV-UED. This
reaction is of fundamental significance to a wide range of fields,
including nuclear engineering, space travel, cancer treatment and
environmental remediation.



FULL STORY ========================================================================== Researchers at the Department of Energy's SLAC National Accelerator
Laboratory have uncovered a key step in the ionization of liquid water
using the lab's high-speed "electron camera," MeV-UED. This reaction
is of fundamental significance to a wide range of fields, including
nuclear engineering, space travel, cancer treatment and environmental remediation. Their results were published in Sciencetoday.


==========================================================================
When high-energy radiation hits a water molecule, it triggers a series
of ultrafast reactions. First, it kicks out an electron, leaving behind
a positively charged water molecule. Within a fraction of a trillionth
of a second, this water molecule gives up a proton to another water
molecule. This leads to the creation of a hydroxyl radical (OH) -- which
can damage virtually any macromolecule in an organism, including DNA,
RNA and proteins -- and a hydronium ion (H3O+), which are abundant in
the interstellar medium and tails of comets, and might contain clues
about the origin of life.

Capturing the unstable pair In a previous Science paper published in 2020,
a team led by scientists at the DOE's Argonne National Laboratory used
SLAC's Linac Coherent Light Source (LCLS) X-ray laser to witness, for the
first time, the ultrafast proton transfer reaction following ionization
of liquid water. But until now, researchers had yet to directly observe
the hydroxyl-hydronium pair.

"All laser surgeries and radiotherapies produce this unstable complex,
which may lead to many chemical reactions in the human body," says
SLAC scientist and study lead Ming-Fu Lin. "Interestingly, this complex
also helps to purify our drinking water by killing germs. It is also of importance in nuclear power generation where water is ionized by other
forms of radiation. Many simulations predict the existence of this
complex but now we have finally observed its formation." To observe
the short-lived hydroxyl-hydronium pair, the researchers created 100-nanometer-thick jets of liquid water - about 1,000 times thinner
than the width of a human hair -- and ionized the water molecules with
intense laser light. Then they probed the molecules with short pulses of high-energy electrons from MeV-UED to generate high-resolution snapshots
of the ionization process. This allowed them to measure bonds between
oxygen atoms and bonds between oxygen and hydrogen atoms at the same time,
thus capturing this important but unstable complex.

Opening a window on chemical reactions To follow up, the researchers
plan to increase the imaging speed so the proton transfer process can
be measured directly prior to the formation of the hydroxyl-hydronium
pairs. They also hope to observe the ejected electron in the liquid
water to better understand how it affects the process.

"Both topics have been intensively studied by simulations, but no
direct structural measurements have been taken to validate theories,"
says Matthias Ihme, an associate professor in the Stanford University Mechanical Engineering department who led the theoretical analysis. "These measurements are also critical for testing our theoretical models that
predict these processes." "Many intermediate states and structures
in chemical reactions are either unknown or have yet to be observed
directly," adds Xijie Wang, a SLAC distinguished staff scientist and
study collaborator. "We can use MeV-UED to explore and capture various short-lived and important complexes, opening a window to study chemical reactions as they occur." MeV-UED is an instrument of the LCLS user
facility, operated by SLAC on behalf of the DOE Office of Science,
which funded this research.

========================================================================== Story Source: Materials provided by
DOE/SLAC_National_Accelerator_Laboratory. Original written by Ali
Sundermier. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. M.-F. Lin, N. Singh, S. Liang, M. Mo, J. P. F. Nunes, K. Ledbetter,
J.

Yang, M. Kozina, S. Weathersby, X. Shen, A. A. Cordones,
T. J. A. Wolf, C. D. Pemmaraju, M. Ihme, X. J. Wang. Imaging
the short-lived hydroxyl- hydronium pair in ionized liquid
water. Science, 2021; 374 (6563): 92 DOI: 10.1126/science.abg3091 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211002123011.htm

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