Determination of the rate coefficients of the SO2 + O + M → SO3 + M reaction

Abstract Rate coefficients of the title reaction R31 (SO2 + O + M → SO3 + M) and R56 (SO2 + HO2→ SO3 + OH), important in the conversion of S(IV) to S(VI), were obtained at T = 970–1150 K and ρave = 16.2 μmol cm−3 behind reflected shock waves by a perturbation method. Shock‐heated H2/O2/Ar mixtures were perturbed by adding small amounts of SO2 (1%, 2%, and 3%) and the OH temporal profiles were then measured using laser absorption spectroscopy. Reaction rate coefficients were elucidated by matching the characteristic reaction times acquired from the individual experimental absorption profiles via simultaneous optimization of k31 and k56 values in the reaction modeling (for satisfactory matches to the observed characteristic times, it was necessary to take into account R56). In the experimental conditions of this study, R31 is in the low‐pressure limit. The rate coefficient expressions fitted using the combined data of this study and the previous experimental results are k31,0/[Ar] = 2.9 × 1035 T−6.0 exp(−4780 K/T) + 6.1 × 1024 T−3.0 exp(−1980 K/T) cm6 mol−2 s−1 at T = 300–2500 K; k56 = 1.36 × 1011 exp(−3420 K/T) cm3 mol−1 s−1 at T = 970–1150 K. Computer simulations of typical aircraft engine environments, using the reaction mechanism with the above k31,0 and k56 expressions, gave the maximum S(IV) to S(VI) conversion yield of ca. 3.5% and 2.5% for the constant density and constant pressure flow condition, respectively. Moreover, maximum conversions occur at rather higher temperatures (∼1200 K) than that where the maximum k31,0 value is located (∼800 K). This is because the conversion yield is dependent upon not only the k31,0 and k56 values (production flux) but also the availability of H, O, and HO2 in the system (consumption flux). © 2010 Wiley Periodicals, Inc. * This article is a U.S. Government work and, as such, is in the public domain of the United States of America. Int J Chem Kinet 42: 168–180, 2010