New method offers first look at super-cold carbon molecules

March 15, 2018, Air Force Office of Scientific Research
Dr. Willliam Lewis, AFRL Senior Research Chemist with the Turbine Engine Division, Aerospace Systems Directorate, configures the laser to scan an infrared spectrum for the Cluster Assembly and Spectroscopy Instrument. With the CAASI, their lab was able to measure the rotationally-resolved infrared spectrum of the C3 molecule trapped in helium droplets at a temperature of -272.78 degrees Celsius. Credit: U.S. Air Force Photo/Staff Sgt. Ashley Clingerman

Science just got a little cooler in the Air Force Research Laboratory. Using a helium droplet method that chills molecular species to nearly absolute zero, researchers in the Aerospace Systems Directorate's Turbine Engine Division are able see carbon clusters, including soot precursors in combustion, in a completely new way.

"Our AFRL team recently scored an important breakthrough and were the first people to see the spectrum of the C3 molecule at record [-272.78 degrees C]," said Dr. William Lewis, AFRL Senior Research Chemist with the Turbine Engine Division, Aerospace Systems Directorate. The C3 molecule is a soot precursor often found in flames, explosions, and other combustion processes, as well as astronomical bodies such as comets and stars. This discovery is key to improving a variety of models used in propulsion and space vehicle applications, he said.

A few years ago, the Fuels and Energy Branch became interested in from the propulsion point of view. Since then, AFRL researchers have rapidly developed a new research capability to measure the energetics and structures of .

"It's a way to freeze ," Lewis said. "This lets us slow everything down. It lets us take what would normally be too fast to even see, then preserve it long enough to see it on a human-perceptible or human-measurable time scale."

Barbara Miller, University of Dayton Research Institute Research Chemist and UDRI Team lead contractor, aligns the carbon evaporation source inside the Cluster Assembly and Spectroscopy Instrument. Credit: U.S. Air Force Photo/Staff Sgt. Ashley Clingerman

"Normally, when you get carbon, it's very hot and other things don't want to stick to it, and you can't capture that interaction and investigate the fundamental steps of the chemistry. If you get it cold enough, then you can bring the carbon molecule that you are interested in together with some collision partner that would be important for whatever application that you are trying to understand," said Lewis.

However, the team discovered that it was not all about cooling the to such low temperatures. Previous attempts to study C3 soot precursors evaporated the C3 and then trapped it in solid neon or argon ice. This was a problem when studying precursor structures and chemical interactions because the can't move in the ice.

AFRL's method relies on submerging the molecule in a helium liquid, allowing the molecule to still move and rotate. So another key advantage of the new method is the ability to investigate interactions with other molecules and study the structures they make together. This is something that researchers haven't been able to do before.

"It can still wiggle. The method is able to cool things down—but cool them down in a way that they don't really perturb the molecular structure, while we use infrared spectroscopy to study the molecules," Lewis added.

Dr. William Lewis, AFRL Senior Research Chemist with the Turbine Engine Division, Aerospace Systems Directorate, and Barbara Miller, University of Dayton Research Institute Research Chemist and UDRI Team lead contractor, record the infrared spectrum of the C3 molecules at a temperature of -272.78 degrees Celsius in the Cluster Assembly and Spectroscopy Instrument. The super low temperature spectrum allows them to clearly determine the structure and bonding in the C3 molecule. Credit: U.S. Air Force Photo/Staff Sgt. Ashley Clingerman

The possibilities are endless. A logical consequence would be to use this data and data from follow-on experiments where they interact it with combustion-relevant and space chemistry molecules and use that data to improve current chemistry models.

"Whether it's a fuel application in terms of the emissions that are going to come out of a combustor, whether it's some chemistry that is going to happen in space, what flow is going to happen around a reentering space vehicle, you need to be able to understand the fundaments steps in chemistry. This helps us do that because then we can take the molecules that we are interested in and bring them together, and let them talk to each other and then just listen in on the conversation," Lewis added.

In the turbine engine community, an improved chemistry model could reduce sooting in emissions and possibly improve combustion efficiency. The space vehicles community would see a different payoff. Carbon molecules that evaporate from space vehicles react with the surrounding air, creating their own type of combustion during reentry. The chemistry in the flow layers around the vehicle changes how it flies. Improved chemical models can lead to an improved ability to control the vehicle upon reentry.

Explore further: Painting a clear picture of how nitrogen oxides are formed

Related Stories

Painting a clear picture of how nitrogen oxides are formed

March 12, 2018

Nitrogen oxides (NOx) are some of the most significant pollutants in our atmosphere—they contribute to the formation of smog, acid rain and ground-level ozone. Because of this, combustion researchers and engine companies ...

Less is more when it comes to soot

April 5, 2016

Small particles emitted into air during the burning of hydrocarbon fuels damage the human respiratory system and enhance the greenhouse effect. In their agglomerated form, these particles form soot that consists predominantly ...

Recommended for you

Study tracks inner workings of the brain with new biosensor

August 16, 2018

An international team of scientists have taken an important step towards gaining a better understanding of the brain's inner workings, including the molecular processes that could play a role in neurological disorders.  

Cryo-electron microscopy sheds new light on batteries

August 16, 2018

The interface of the solid anode and the liquid electrolyte plays a crucial role in the performance of a lithium-metal battery, but characterizing the processes that happen at that intersection has been a challenge.

World's oldest cheese found in Egyptian tomb

August 15, 2018

Aging usually improves the flavor of cheese, but that's not why some very old cheese discovered in an Egyptian tomb is drawing attention. Instead, it's thought to be the most ancient solid cheese ever found, according to ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.