Laboratory experiments of HO_2 reactions with peroxy radicals using infrared kinetic spectroscopy (IRKS)

Abstract

The reaction of HO_2 with acetyl peroxy radical, CH_3C(O)O_2, has been suggested to proceed via three channels [1]:(a) HO_2 + CH_3C(O)O_2 → CH_3C(O)O_2H + O_2(b) HO_2 + CH_3C(O)O_2 → CH_3C(O)OH + O_3(c) HO_2 + CH_3C(O)O_2 → CH_3C(O)O + OH + O_2Channel (c) is of particular interest not only because of the lack of prodn. of ozone, but also the formation of the hydroxyl radical, OH, a key oxidizing radical in the earth's atm. The results from several independent studies [2,3,4] have shown that the branching ratio of (c) is close to 0.40. Although the results show strong evidence that channel (c) is a significant branch of the reaction of acetyl peroxy radical with HO_2, all expts. were only done at room temp. (298 K) and none of the expts. used techniques that allowed for the measurement of either of the two reacting species. Another concern is that the overall reaction rates of acetyl peroxy radical with HO_2 obtained by the expts. have shown large discrepancies. Furthermore, there is very little information on the temp. dependence of this reaction at upper troposphere temps. The results have led to upper and lower bound ests. by the JPL Data Evaluation panel that differ by almost an order of magnitude. The current study has employed a powerful method called IR Kinetic Spectroscopy (IRKS) for studying radical reactions. In the presented work, this technique is used to study the consumption of HO2 by CH_3C(O)O_2. Specifically, the kinetic rate consts. of this reaction is detd. as a function of temp. (220 to 298 K) and pressure (50 to 400 torr) by simultaneously measuring the disappearance of HO_2 using near-IR spectroscopy and of CH_3C(O)O_2 using UV spectroscopy at a wavelength where HO_2 does not absorb.[1] Hasson, A. S., Tyndall, G. S., Orlando, J. A, 2004, 108 (28), 5979-5989.[2] Crawford, M. A., Wallington, T. J., Szente, J. J., Maricq, M. A, 1999, 103 (3), 365-378.[3] Dillon, T. And Crowley, J. Discuss., 2008, 8, 7111-7148.[4] Moortgat, G. K., Veyret, B., Lesclaux, R. 1989, 160 (4) 18, 443-447.