A kinetic study of the reaction of atomic oxygen with SO2

The effective second-order rate constant for O + SO2 (+Ar) -> SO3 (+Ar) has been measured by pulsed laser-photolysis with resonance fluorescence detection of atomic oxygen under pseudo-first-order conditions. The pressure dependence was determined at five temperatures in the range 290-840 K. The results obtained at pressures up to 880 mbar reveal fall-off behavior. With an estimated broadening parameter F-c, Troe fits to the measurements yield the low-pressure limit k(0) = 9.5 x 10(-23) T-3 exp(-2400/T) cm(6) molecule(-2) s(-1) and the high-pressure limit k(infinity) = 6.1 x 10(-13) exp (-850/T) cm(3) molecule(-1) s(-1). An RRKM extrapolation of the present k(0) values yields k(0) = 6.7 x 10(-21) T-3.6 exp(-2610/T) cm(6) molecule(-2) s(-1), which is in good accord with several literature values over 220-2500 K. At low temperatures, k(0) shows a positive activation energy rationalized in terms of a barrier of 15.9 kJ mol(-1), and k(0) reaches a maximum at around 750 K. Our expression for k(infinity) is in order-of-magnitude accord with values used to model a flow reactor and indicates a small pre-exponential factor. This may reflect the probability of triplet-singlet transitions in the spin-forbidden addition reaction and/or a tight transition state. (c) 2004 The Combustion Institute. Published by Elsevier Inc. All rights reserved.