New discovery may be key to controlling chemical reactions

Tuesday, February 7, 2023

Hand dropping yellow dye into a beaker of water.

A new study published today in Nature is changing our understanding of chemical reactions and overturning previous theoretical models by finding an unexpected resonance frequency during the reaction of two molecules.

Resonance is when one object vibrating at the same natural frequency as a second object forces that second object into vibrational motion.

This ground-breaking finding is the first time a resonance has been observed between two ultracold molecules and is a stepping-stone for researchers to learn about and control the molecules that comprise our universe.

Portrait of Alan Jamison“Resonances occur when vibrations at a specific frequency get preferentially amplified. For example, when a piano string gets hit by the hammer, it vibrates at a specific frequency based on the length and thickness, creating a musical note unique to that string,” said Dr. Alan Jamison. “Similar resonances occur in atoms, where very specific frequencies of energy create stronger than expected responses in the chemical systems.”

Previously predicted to be an impossibility, Jamison and his collaborators from the Massachusetts Institute for Technology (MIT) were able to observe resonant frequencies in a chemical reaction between two ultracold molecules. By cooling down sodium-lithium molecules to near-absolute zero temperatures, the team could control the reactions at a quantum level. Without such control, the unusual resonance would never have been noticed.

“These seemingly simple systems still have a lot of surprising complexity hiding inside – Schrödinger wrote down his equation 100 years ago, but we still can’t solve it for a four-atom system,” said Jamison, an assistant professor in the Department of Physics and Astronomy and member of the Institute for Quantum Computing (IQC). “We’re pushing the frontier of understanding complex quantum dynamics.”

The research team probed the four-atom transition state with a magnetic field over a range of one million milligauss, a unit of measurement for the magnetic field strength. Within this search region, the resonant frequency found was only 25 milligauss wide.

“It was like finding a needle in a haystack,” said Dr. Wolfgang Ketterle, a professor at MIT. “When the magnetic field was tuned to this specific frequency, the chemical reaction was dramatically sped up.”

The discovery of these resonances holds promise for future applications in controlling chemical reactions. For example, an enhanced resonance may one day steer a chemical reaction or promote the formation of a desired product which would be less favourably made under non-resonance conditions, opening a new avenue and investigation tool for guiding molecular reactions.

The study, A Feshbach resonance in collisions between triplet ground state molecules, by Jamison, Ketterle, Juliana Park, Yu-Kun Lu and Dr. Timur Tscherbul, was published in Nature.