MIT physicists observe rare resonance in molecules for first time

A team of Massachusetts Institute of Technology (MIT) physicists has witnessed resonance in colliding ultracold molecules, a discovery that ultimately could provide a clue to the forces that drive molecules to chemically react and eventually provide a way to control chemical reactions.

According to an MIT news release, Wolfgang Ketterle, the John D. MacArthur Professor of Physics at the university, explained that his team’s work marks the first time anyone has witnessed a resonance between two ultracold molecules.

“There were suggestions that molecules are so complicated that they are like a dense forest, where you would not be able to recognize a single resonance,” Ketterle said in the release. “But we found one big tree standing out, by a factor of 100. We observed something completely unexpected.”

According to MIT, Ketterle was joined by co-authors, including lead author and MIT graduate student Juliana Park, graduate student Yu-Kun Lu, former MIT postdoc Alan Jamison, currently at the University of Waterloo, and Timur Tscherbul at the University of Nevada.

MIT noted in the release that resonance happens at the smaller scale of atoms and molecules. It noted when particles have a chemical reaction, it is often the result of a set of specific conditions that resonate with particles in a fashion that leads to a chemical connection.

Moreover, the research team noted that with molecules and atoms in a constant state of motion, they reside in a blur of rotating and vibrating states, making the selection of the right resonating state that could trigger molecules to react virtually impossible.

It turns out that collisions occur constantly within a cloud of molecules, with particles dancing off each other like a ball inside a pinball machine. The particles may bounce off one another or could connect in a brief but important state dubbed “intermediate complex” that sparks a reaction to change the particles into a new chemical structure.

MIT noted the research team sought evidence of resonance in atoms and molecules that are super-cooled to temperatures just above absolute zero. The team said these conditions slow the particles’ random motion, which is driven by temperature. The release added that this provided a window for witnessing any more subtle signs of resonance.

“When two molecules collide, most of the time they don’t make it to that intermediate state,” Jamison said in the release. “But when they’re in resonance, the rate of going to that state goes up dramatically.”

According to MIT, the research team also discovered that a cloud of super-cooled sodium-lithium (NaLi) molecules disappeared 100 times faster than usual when exposed to a very specific magnetic field. The release said the rapid disappearance of the molecules serves as a signal that the magnetic field shifted the particles into a resonance and, as a result, they would react more rapidly than normal.

“The intermediate complex is the mystery behind all of chemistry,” Ketterle added. “Usually the reactants and the products of a chemical reaction are known but not how one leads to the other. Knowing something about the resonance of molecules can give us a fingerprint of this mysterious middle state.” MIT concluded.

MIT concluded that the discovery unlocks a greater understanding of chemistry and molecular dynamics. Although the team does not expect to stimulate resonance, its results could one day result in the ability to use the natural resonances of a particle to manipulate chemical reactions.