Chemical Kinetic Studies Using Ultraviolet Cavity Ring-Down Spectroscopic Detection: Self-Reaction of Ethyl and Ethylperoxy Radicals and the Reaction O2 + C2H5 → C2H5O2

A laser photolysis reactor that uses cavity ring-down spectroscopic (CRDS) detection was characterized and used to measure the rate coefficients of three benchmark reactions of known importance to ethane oxidation. At 295 K and approximately 700 Pa (5.5 Torr) total pressure, we obtained the self-reaction rate coefficients of k = (1.99 ± 0.44) × 10 -11 cm 3 molecule -1 s -1 for C 2 H 5 + C 2 H 5 and k = (7.26 ± 2.4) × 10 -14 cm 3 molecule -1 s -1 for C 2 H 5 O 2 + C 2 H 5 O 2 . We obtained k = (2.7 ± 0.3) × 10 -12 cm 3 molecule -1 s -1 for the pseudo-first-order association reaction O 2 + C 2 H 5 + Ar. We also measured the absorption cross sections of the ethyl radical, σ 220 = (252 ± 42) × 10 -20 cm 2 molecule -1 and σ 222 = (206 ± 42) × 10 -20 cm 2 molecule -1 . Stated uncertainties are 2σ. The new rate coefficients agree with those obtained previously by other methods. The agreement confirms that ultraviolet CRDS detection is a viable tool for experimental determinations of gas-phase radical−radical and radical−molecule reaction rate coefficients.