Session: Physical Chemistry Poster:

Radical-radical reactions play an important role in combustion systems. Among the radicals in combustion, resonantly stabilized radicals (RSRs) are of particular importance as they can accumulate within these systems due to increased stability from resonance. Because molecular oxygen is slow to react with RSRs, these radicals are consumed by other radicals present in these systems. Among RSRs, the propargyl radical (C₃H₃) has garnered significant interest for study as it is an important precursor to polyaromatic hydrocarbons, most notably benzene, via self-recombination. The formation of these polyaromatic hydrocarbons pose a problem in both environmetal health and combustion efficiency. The OH radical is an abundant species in combustion that is likely responsible for the consumption of significant amounts of propargyl radicals in flames and other combustion systems.

Data were taken at the Advanced Light Source in Berkeley using the experimental setup constructed by Sandia National Labs. The experimental setup uses photoionization mass spectrometry to probe the products for the propargyl + OH reaction. Tuning the synchrotron radiation allows for the discrimination between product isomers due to the unique pattern and ionization energy that exists for different isomers.

Both ends of the propargyl radical has a site for radical addition. The “head” addition (the CH₂ site) of OH results in the isomer allenol while the “tail” reaction will form propargyl alcohol. At room temperature, the major products of the reaction are found to be allenol, acrolein, and cyclopropene, with acrolein making up ~75% of m/z 56 signal. As temperature increases up to 800K, acrolein becomes nearly all of the contributing signal. This analysis allows for better understanding of the mechanism of the propargyl + OH reaction and how it fits into the larger combustion scheme.

David Osborn

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