Hear that? Mizzou researchers are ‘listening’ to molecules in supersonic conditions

By Brian Consiglio

September 12, 2025
Contact: Brian Consiglio, [email protected]

What happens when you hurl molecules faster than sound through a vacuum chamber nearly as cold as space itself? At the University of Missouri, researchers are finding out - and discovering new ways to detect molecules under extreme conditions.

The discovery could one day help chemists unravel the mysteries of astrochemistry, offering new clues about what the universe is made of, how stars and planets form and even where life originated.

In a recent study, Mizzou faculty member Arthur Suits and doctoral student Yanan Liu fired a laser at methane gas molecules moving faster than the speed of sound in a vacuum chamber roughly negative 430 degrees Fahrenheit, close to the temperature in parts of outer space.

Because the molecules were emitted through a rocket nozzle, a supersonic flow was created. The laser's light was absorbed by the molecules, making them "excited" and vibrate against each other. Those vibrations created tiny pressure waves - actual sound - that Suits captured with a super sensitive microphone.

This process of using light to make sound - known as photoacoustic spectroscopy - was previously thought to be impossible in extreme conditions that mimic outer space. This is because an extremely cold, vacuum-like environment has nothing to carry sound. Besides, how can you hear something traveling faster than the speed of sound?

Yet Suits and his team at Mizzou found it can be done: The excitation of the molecules is converted to sound at the point when the molecules smash against the microphone.

"We use the tools of physics to understand how chemistry happens at the highest level of detail possible," said Suits, a Curators Distinguished Professor in the College of Arts and Science. "For example, by better understanding exactly how much rotation or vibration an individual molecule has, we can start to gain more fundamental knowledge about the universe we live in, furthering our understanding of astrochemistry."

Suits' research has been funded by the U.S. Department of Defense, the National Science Foundation and the U.S. Department of Energy throughout his career due to his work having broad applications in astrochemistry and the aviation, manufacturing and energy industries.

"This research can ultimately help us start to better understand the chemical reactions occurring in interstellar conditions - the space between stars - by studying chemical reactions in a laboratory under similar conditions," Suits said. "Now that we have discovered a new way to detect molecules at extremely low temperatures, we can start to use this laser technology to excite a lot of different molecules beyond just methane gas, and we can see what else we can learn."

"Photoacoustic spectroscopy in a supersonic flow" was published in the Journal of Physical Chemistry A.