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

Published

May 1, 1999

Author(s)

D B. Atkinson, Jeffrey W. Hudgens

Abstract

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.

Citation

Journal of Physical Chemistry A

Volume

103

Pub Type

Journals

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Keywords

C₃H₃+C₃H₃ reaction, C₃H₃+O₂ reaction, cavity ring-down spectroscopy, dihalopropyl radical, electronic spectrum, propargyl radical, propargylperoxy radical, reaction rate coefficient, self-reaction rate coefficient

Citation

Atkinson, D. and Hudgens, J. (1999), 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 July 17, 2024)