Rate of the O + SO3 reaction

The rate of the O + SO3 reaction has been measured under pseudo−first−order conditions in a discharge flow reactor with ESR detection. The reaction is shown to be a fast third−order process at pressures up to 7 torr, a fact not brought out in previous work. Third−order rate constants obtained for M = He at 298, 385, and 507°K are 7.3±0.2, 3.8±0.2, and 2.4±0.2×1017 cm6 mole−2⋅sec−1, respectively, the data obeying k = 5.0×1016 exp(785/T) in this range. At 298°K, the ratio k (M = N2)/k (M = He) is 1.4, and it is shown that the ratio k (M = SO3)/k (M = He) probably cannot be greater than about 10. The reaction products are written as SO2 + O2, no evidence being found for a stable SO4 in the gas phase. Analogous measurements on N + SO3 indicate it is too slow to measure by this technique (bimolecular rate constant <6×106 cm3 mole−1⋅sec−1), in disagreement with other reported results.