Sandia researchers are the first to directly measure hydroperoxyalkyl radicals—a class of reactive molecules denoted as “QOOH”—that are key in the chain of reactions that controls the early stages of combustion. This breakthrough has generated data on QOOH reaction rates and outcomes that will improve the fidelity of models used by engine manufacturers to create cleaner and more efficient cars and trucks.
A paper, “Direct observation and kinetics of a hydroperoxyalkyl radical (QOOH),” describing the work, performed by David Osborn, Ewa Papajak, John Savee, Craig Taatjes and Judit Zádor (all in 8353) at Sandia’s Combustion Research Facility, is featured in the Feb. 6 edition of Science.
“We needed a specialized strategy to create enough QOOH radicals to detect, and we needed to determine the spectral fingerprint of a QOOH molecule, so that we would recognize it if we created it.” Chemist John Savee came up with that strategy. Putting his knowledge of combustion chemistry to work, Savee helped pinpoint the best fuel for producing a detectable QOOH. He chose cycloheptadiene, a molecule with seven carbon atoms arranged in a ring.
Initial experiments seemed to prove Savee’s ideas were right, and the team turned to its computational experts, Papajak and Zádor, who used quantum chemistry to predict what the experimentalists should have observed. Agreement between the two approaches would aid in confirming the discovery.
For the direct measurements, the team moved the Sandia-designed Multiplexed Photoionization Mass Spectrometer (MPIMS) to the Advanced Light Source, a LBNL synchrotron user facility. The intense tunable light created by the synchrotron allowed the team to measure spectral fingerprints of molecules, deducing the particular arrangement of atoms that gives a molecule its identity.
They confirmed that the spectrum of the radical they observed matched that predicted by Papajak and Zádor, showing that it was in fact a QOOH molecule, rather than some other possible arrangement of the same atoms.
Read the Sandia news release.