On the tiniest of scales, chemistry isn't all about 'billiard-ball'
reactions

Date:
January 18, 2022
Source:
University of Missouri-Columbia
Summary:
In a recent study, scientists provide evidence of the effects of
photodissociation on the quantum level for an atmospheric pollutant,
formaldehyde, thereby showing photodissociation reactions can't
be treated classically, like 'billiard-balls' coming together,
colliding and reconnecting, said an author of a new study.



FULL STORY ========================================================================== Scientists are now one step closer to better understanding how to live in
a "quantum" world -- and not just from watching the character "Ant-Man"
in the Marvel movie franchise.


========================================================================== Take, for instance, a microscopic view of the delicate, protective barrier
of the Earth's atmosphere that creates the ozone layer and protects
life as we know it. Inside that layer of air, oxygen molecules are under
near constant attack by solar ultraviolet (UV) rays that break up these molecules through a chemical process known as photodissociation. While
this process is invisible to the naked eye, scientists can observe these micro-interactions on the smallest of scales -- the quantum level.

In a study recently published in Science, scientists at the University
of Missouri provide evidence of the effects of photodissociation on
the quantum level for an atmospheric pollutant, formaldehyde, thereby
showing photodissociation reactions can't be treated classically, like "billiard-balls" coming together, colliding and reconnecting, said Arthur Suits, Curators Distinguished Professor of Chemistry in the MU College
of Arts and Science, and a co-corresponding author on the study.

"By only thinking of chemical reactions in the classic sense with
'billiard balls,' a chemist is going to miss out on what a molecule
is truly doing," Suits said. "It is well known that quantum effects
are very important as a molecule gets very cold. What is surprising
here is that strong quantum effects appear at the high energy of photodissociation. This new insight could change not only our view of how
the molecule behaves, but may also impact the overall chemical makeup,
and that in turn could cause the chemistry to go in unexpected ways
because of this added dimension of the quantum properties." The new
study concerns roaming in which photodissociation breaks a molecule into pieces, but the pieces come back and react with each other. Until now, "billiard ball" models could completely match such experiments. The
study shows more detailed measurements cannot be treated this way.

Instead, they have to use a more complicated quantum model to confirm
the unusual properties they are observing. Suits believes their findings
could one day help scientists develop a better theoretical understanding
of the chemistry in the atmosphere, both in the stratosphere where ozone protects us, and at ground level where it is a dangerous pollutant.

"If you want to understand the chemistry of the atmosphere, for example,
you first need to understand what happens when light is absorbed and
a molecule starts to dissociate," Suits said. "Chemists may think
they don't have to worry about what is going on at the quantum level
in photodissociation, and it's just the classic billiard-ball effect
of atoms, but we show here that's not always the case, and chemists
need to be able to refine their intuition to a certain extent."
"Orbiting resonances in formaldehyde reveal coupling of roaming, radical,
and molecular channels," was published in Science. Co-authors include
Casey Foley at MU, and Hua Guo and Changjian Xie from the University of
New Mexico. Xie also has a dual appointment with Northwest University
in China.

Funding was provided by grants from the Army Research Office
Multidisciplinary University Research Initiative (W911NF-19-1-0283 and W911NF-17-1-0099) and the National Natural Science Foundation of China (22073073). The content is solely the responsibility of the authors and
does not necessarily represent the official views of the funding agencies.

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


========================================================================== Journal Reference:
1. Casey D. Foley, Changjian Xie, Hua Guo, Arthur G. Suits. Orbiting
resonances in formaldehyde reveal coupling of roaming, radical,
and molecular channels. Science, 2021; 374 (6571): 1122 DOI:
10.1126/ science.abk0634 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220118154845.htm

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