Rate Coefficients for the Propargyl Radical Self-Reaction and Oxygen Addition Reaction Measured Using Ultraviolet Cavity Ring-down Spectroscopy

Abstract

By using 193 nm laser photolysis and cavity ring-down spectroscopy to produce and monitor the propargyl radical (CH2CCH), the self-reaction and oxygen termolecular association rate coefficients for the propargyl radical were measured at 295 K between total pressures of 300 Pa and 13300 Pa (2.25 and 100 Torr) in Ar, He, and N2 buffer gases. The rate coefficients obtained by simple second-order fits to the decay data were observed to vary with the photolytic precursors: allene, propargyl chloride, and propargyl bromide. By using a numerical fitting routine and more comprehensive mechanisms, a distinct rate coefficient for the self-reaction was determined, k∞(C3H3+C3H3) = (4.3 ± 0.6) × 10-11 cm3 molecule-1 s-1 at 295 K. This rate coefficient, which is a factor of 2.8 times slower than reported previously, was independent of total pressure and buffer choice over the entire pressure range. Other rate coefficients derived during the modeling included k(C3H3+H 665 Pa He) = (2.5 ± 1.1) × 10-10 cm3 molecule-1 s-1...