A kinetic study of the reaction of atomic oxygen with SO2

Abstract The effective second-order rate constant for O + SO 2 (+Ar) → SO 3 (+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 × 10 −23 T −3  exp (−2400/ T ) cm 6  molecule −2  s −1 and the high-pressure limit k ∞  = 6.1 × 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 × 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 ∞ 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.