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On the smallest scale, chemistry is not just about “billiard ball” reactions

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Scientists are now one step closer to understanding how to live in a "quantum world" - and not just from seeing the character "Ant-Man" in the Marvel movie series.

Take, for example, a microscopic image of the delicate, protective barrier of the Earth's atmosphere that creates the ozone layer and protects life as we know it. Inside that air layer, oxygen molecules are under almost constant attack by the sun's ultraviolet (UV) rays, which 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 scale - the quantum level.

In a study recently published in Science, researchers at the University of Missouri present evidence of the effects of photodissociation at the quantum level of an atmospheric pollutant, formaldehyde, thereby showing that photodissociation reactions cannot be treated classically, like billiard balls colliding, colliding and reconnecting, said Arthur Suits, Curators Distinguished Professor of Chemistry at MU College of Arts and Science, and a co-corresponding author on the study.

"By thinking only of chemical reactions in the classical sense with 'billiard balls', a chemist will miss out on what a molecule really does," Suits said. "It is well known that quantum effects are very important when a molecule gets very cold. What is surprising here is that strong quantum effects occur at the high energy of the photodissociation. This new insight can not only change our view of how the molecule "but can also affect the overall chemical composition, and this in turn can cause the chemistry to go in unexpected ways because of this extra dimension of quantum properties."

The new study deals with roaming, where 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 that more detailed measurements can not be processed in this way.

Instead, they need to use a more complicated quantum model to confirm the unusual properties they observe. Suits believes that their results may one day help scientists develop a better theoretical understanding of chemistry in the atmosphere, both in the stratosphere, where ozone protects us, and on the earth's surface, where it is a dangerous pollutant.

"To understand the chemistry of the atmosphere, for example, you first have to understand what happens when light is absorbed and a molecule begins to dissociate," Suits said. "Chemists may think they do not have to worry about what is going on at the quantum level in photodissociation, and that's just the classic billiard ball effect of atoms, but we show here that this is not always the case and chemists need to be able to to refine their intuition to some degree. "

"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 of the University of New Mexico. Xie also has a dual agreement with Northwest University in China.

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More information: Casey D. Foley et al, Orbiting resonances in formaldehyde reveal coupling of roaming, radical and molecular channels, Science (2021). DOI: 10.1126 / science.abk0634
Provided by the University of Missouri

Citation: On the smallest scale, chemistry is not just about 'billiard ball' reactions (2022, 18 January) retrieved 19 January 2022 from isnt- billiard-ball.html

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