'Roaming reactions' study to shed new light on atmospheric molecules


Date:
August 6, 2020
Source:
University of New South Wales
Summary:
For the first time, a team of chemists has lifted the hood on the
mechanics involved in the mysterious interplay between sunlight
and molecules in the atmosphere known as 'roaming reactions',
which could make atmospheric modelling more accurate.



FULL STORY ==========================================================================
A detailed study of roaming reactions -- where atoms of compounds
split off and orbit other atoms to form unexpected new compounds --
could enable scientists to make much more accurate predictions about
molecules in the atmosphere, including models of climate change, urban pollution and ozone depletion.


==========================================================================
In a paper published today in the journal Science, a team of researchers
from UNSW Sydney, University of Sydney, Emory University and Cornell
University showed in unprecedented detail exactly what happens during
roaming reactions of chemical compounds.

Professor Scott Kable, an atmospheric scientist who is also the head
of UNSW's School of Chemistry, likens the study to lifting the hood
on roaming reactions and seeing for the first time how the parts fit
together. He says the study will give scientists new tools to understand
the machinations of reactions in the atmosphere.

"Chemical reactions, where atoms are rearranged to make new substances,
are occurring all the time in our atmosphere as a result of natural
emission from plants and animals as well as human activity," Prof
Kable says.

"Many of the key reactions in the atmosphere that contribute to
photochemical smog and the production of carbon dioxide are initiated
by sunlight, which can split molecules apart.

"For a long time, scientists thought these reactions happened in a
simple way, that sunlight was absorbed and then the molecule explodes,
sending atoms in different directions.



========================================================================== "But, in the last few years it was found that, where the energy from
the sun was only just enough to break a chemical bond, the fragments
perform an intimate dance before exchanging atoms and creating new, unanticipated, chemical products -- known as roaming reactions.

"Our research shows these 'roaming' reactions exhibit unusual and
unexpected features." Prof Kable says in an experiment detailed in the
paper, the researchers looked at the roaming reaction in formaldehyde
(CH2O) and were surprised to see instead, two quite distinct signals,
"which we could interpret as two distinct roaming mechanisms." Professor
Joel Bowman, who oversaw simulations of the roaming reactions at Emory University in the US, observed that that "detailed modelling of these
reactions not only agree with the experimental findings, they provide
insight into the motion of the atoms during the reaction." Simulations
of the experiment were also carried out at Cornell University (US).

Professor Meredith Jordan from University of Sydney says the experiments
and theory results suggest roaming reactions straddle the classical and
quantum worlds of physics and chemistry.

"Analysing the results with the incredible detail in both experiments
and simulations allowed us to understand the quantum mechanical nature
of roaming reactions. We expect these characteristics to be present in
all roaming reactions," she says.

The results of this study will provide theoreticians with the data needed
to hone their theories, which in turn will allow scientists to accurately predict the outcomes of sunlight-initiated reactions in the atmosphere.

Prof Kable says the study could also benefit scientists working in the
areas of combustion and astrophysics, who use complex models to describe
how molecules interact with each other in gaseous form.


========================================================================== Story Source: Materials provided by University_of_New_South_Wales. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Mitchell S. Quinn, Klaas Nauta, Meredith J. T. Jordan, Joel
M. Bowman,
Paul L. Houston, Scott H. Kable. Rotational resonances in the H2CO
roaming reaction are revealed by detailed correlations. Science,
2020 DOI: 10.1126/science.abc4088 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200806153553.htm

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