The next time you light a match, gaze at the flame: It may look ordinary, but fire contains a world of mystery that chemists have been trying to decipher for nearly two centuries. Even the simplest flames are complicated, a dance of chemical reactions in which molecules interact in hundreds of different ways. While trying to tease apart these reactions, chemists recently stumbled onto a new species of compounds never before seen in flames.
The discovery could lead to cleaner fuels, enhanced atmospheric models, and a solution to the enduring mystery of how soot forms. Researchers from several institutions, working at Sandia National Laboratories in Livermore, California, initially found the molecules—known as enols—in a flame that was produced by ethylene, the substance used to make the common plastic polyethylene. Enols are less stable isomers, or chemical variants, of known molecules that are produced in fire’s many chemical transformations. They pop up briefly and then disappear.
At first, the researchers thought enols might be unique to ethylene flames. So they analyzed 14 other combustibles with a high-energy radiation probe, a supersensitive machine that can pick apart the chemistry of fire. The probe bombards each flame’s exhaust with a high-intensity beam of photons. As the photons strike molecules in the exhaust, ions are ejected that can later be classified. “We shoot the beam into samples from different parts of flame and sort what comes out by mass,” says project member Craig Taatjes. “This tells us the mass of individual molecules so we can get a mass spectrum as a function of the molecule’s position in the flame.”
“There’s a whole class of molecules that’s not in our combustion models,” says Taatjes. The molecules are also found in interstellar space, so learning more about them may shed light on the formation of organic matter in the galaxies.