Nanotechnology

A new way for quantum physics to control chemical reactions

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June 16, 2023

(Nanowerk News) Controlling chemical reactions to produce new products is one of the greatest challenges in chemistry. Developments in this area impact industry, for example by reducing the waste generated in the manufacture of construction materials or by increasing the production of catalysts to speed up chemical reactions.

For this reason, in the field of polariton chemistry – which uses chemical tools and quantum optics – in the last ten years various laboratories around the world have developed experiments in optical cavities to manipulate the chemical reactivity of molecules at room temperature, using electromagnetic fields. . Some have succeeded in modifying the products of chemical reactions in organic compounds, but to date, and without relevant advances in the last two years, no research team has been able to come up with a general physical mechanism to describe the phenomenon and reproduce it to obtain consistently the same measurements.

Now a team of researchers from the Universidad de Santiago (Chile), part of the Millennium Institute for Research in Optics (MIRO), led by principal investigator Felipe Herrera, and the laboratory of the chemistry division of the US Naval Research Laboratory, (United States of America), led by researcher Blake Simpkins , for the first time reported the manipulation of the formation rate of urethane molecules in a solution contained within an infrared cavity. Modification of ground-state chemical reactivity through light-matter coherence in the infrared cavity Illustration of an infrared Fabry-Perot reactor with a urethane formation reaction occurring in solution under the influence of a confined electromagnetic vacuum. (Image: Johan Triana and Alejandra Pantoja)

The findings were published in a journal Science (“Modification of ground-state chemical reactivity via light-matter coherence in the infrared cavity”) and proved, for the first time, both theoretically and experimentally, that it is possible to selectively modify the reactivity of certain bonds in chemical reactions at room temperature in liquid solvents, through the vacuum influence of electromagnetic fields in a narrow range of infrared frequencies. “This theoretical discovery increases our fundamental understanding of the phenomenon compared to other models that only partially explain aspects of experimental observations or only completely deny experimental evidence,” said researcher Felipe Herrera.

A new scientific scope for molecular manipulation

Why is it so difficult to control chemical reactions? When a chemical reaction occurs, the bonds that hold the atoms together in a molecule break and rearrange, forming new substances known as products. For this process to occur, energy is often required, and several physicochemical principles dating back to the 19th century have helped us understand how this transfer of energy occurs according to the laws of thermodynamics.

There is also the principle of reactivity based on molecular structure, as proposed by Eyring, Evans and Polanyi in 1935, widely used in all fields of chemistry. These basic principles imply that any reaction between two molecules is independent of any other chemical reactions that may occur in a solution. “That’s perfectly valid in almost any situation studied in eighty years or so, but the electromagnetic vacuum creates correlations between the various chemical reactions that occur within the volume of the cavity, and the correlations created by electromagnetic fields, in principle making traditional theory assumptions of chemical reactivity questionable,” explained Felipe Herrera.

The experimental contribution of this study is confirmation of reaction rate modification through interaction with a vacuum of electromagnetic fields confined within cavities, using well-studied chemical reactions, and with changes that are more significant than those found with any other reaction type. On the theoretical part, the contribution is the fact that by modifying the dynamics of the chemical bonds that mainly participate in reactions, through the infrared vacuum, it is possible to control the products”, added Johan Triana, postdoctoral fellow at MIRO and the University of Santiago who participated in the creation of mathematical models and calculations numeric for the description of molecular systems.

Reproduce and interpret measurements

The research began in 2020, when a postdoctoral fellow at the US Naval Research Laboratory, now a professor at Bilkent University, Dr. Wonmi Ahn, did the first try.

In 2021 Blake Simpkins prepared a new sample to ensure that measurements are reproducible and improve the liquid cells in which chemical reactions take place.

In the middle of that year, researcher Felipe Herrera began holding regular meetings with Simpkins to explore possible theoretical answers to support the results obtained. “We decided to start from scratch and build a theory that takes into account all the physical aspects of quantum optics, but under certain conditions reduces to the standard theory of theoretical chemical reactivity,” explains USACH professor Felipe Herrera.

The result of the process was the publication “Modification of ground state chemical reactivity through the coherence of light matter in the infrared cavity”, led by Simpkins (US Naval Research Laboratory) and Herrera (MIRO, Universidad de Santiago de Chile), with the participation of researcher Wonmi Ahn, (Bilkent University, Turkey), researcher Johan Triana and PhD student Felipe Recabal, both part of MIRO’s Molecular Quantum Technology group, at USACH.

This first work opens up new possibilities and scientific challenges, Dr. Herrera explains: “We need to develop a fairly simple and general theoretical and mathematical framework that any researcher in the world can use to interpret their experiments and hopefully devise new types of measurements that no one has yet visualized.”

In this regard, Herrera reflects on his ambition as a scientist moving across physics and chemistry: “It would be nice to build a consistent theory that brings together the two most successful disciplines in modern science: chemical kinetics and quantum physics.”



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