CHEMICAL KINETIC STUDIES USING ULTRAVIOLET CAVITY RING-DOWN SPECTROSCOPIC DETECTION: SELF-REACTION OF ETHYL AND ETHYLPEROXY RADICALS AND THE REACTION, O2 + C2H5 --> C2H5O2. Dean B. Atkinson and Jeffrey W. Hudgens, Physical and Chemical Properties Division, Chemical Science and Technology Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899 USA, Building 222, Room A261, (301)-975-5298, dean.atkinson@nist.gov

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) x 10-11 cm3 s-1 for C2H5 + C2H5 and k = 7.26(±2.4) x10-14 cm3s-1 for C2H5O2 + C2H5O2.. We obtained k = 2.7(±0.3) x 10-12 cm3s-1 for the pseudo-first order association reaction, O2 + C2H5 + Ar. We also measured the absorption cross-sections of the ethyl radical, sigma220 = 252(±42) x10-20 cm2 and sigma222 = 206(±42)  x 10-20 cm2. Stated uncertainties are ±2sigma. 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.