Rate Coefficients for the Propargyl Radical Self-Reaction and Oxygen Addition Reaction Measured Using Ultraviolet Cavity Ring-Down Spectroscopy
D B. Atkinson, Jeffrey W. Hudgens
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 298 K between total pressures of 300 Pa and 13,300 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. Using a numerical fitting routine and more comprehensive mechanisms, this variance was removed and a distinct rate coefficient for the self-reaction was determined. We recommend a value of k(C3H3 + C3H3) =4.81.3 H10-11 cm3 molec-1 s-1 at 295 K, independent of total pressure and buffer choice over the entire pressure range. Several other rate coefficients are derived during the modeling, including k(H+C3H3, 665 Pa He) =2.41.0 H10-10 cm3molec-1s-1 and k(Br+C3H3, 665 Pa He)= 1.30.8 H10-10 cm3molec-1 s-1. The association reaction, C3H3 + O2, was found to lie in the falloff region between linear and saturated pressure dependence for each buffer gas (Ar, He and N2) between 300 Pa and 13,300 Pa. A fit of these data derived the high pressure limiting rate coefficient ksalinty}(C3H3+O2)=2.30.5 H10-13 cm3 molec-1 s-1. Three measurements of the propargyl radical absorption cross-section obtained ς332.5= 413 60 x 10-20 molec-1-cm2 at 332.5 nm.
and Hudgens, J.
Rate Coefficients for the Propargyl Radical Self-Reaction and Oxygen Addition Reaction Measured Using Ultraviolet Cavity Ring-Down Spectroscopy, Journal of Physical Chemistry A, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=831530
(Accessed December 10, 2023)