The rate of the O + SO3reaction has been measured under pseudominus;firstminus;order conditions in a discharge flow reactor with ESR detection. The reaction is shown to be a fast thirdminus;order process at pressures up to 7 torr, a fact not brought out in previous work. Thirdminus;order rate constants obtained for M = He at 298, 385, and 507deg;K are 7.3plusmn;0.2, 3.8plusmn;0.2, and 2.4plusmn;0.2times;1017cm6moleminus;2sdot;secminus;1, respectively, the data obeyingk= 5.0times;1016exp(785/T) in this range. At 298deg;K, the ratiok(M = N2)/k(M = He) is 1.4, and it is shown that the ratiok(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 SO4in the gas phase. Analogous measurements on N + SO3indicate it is too slow to measure by this technique (bimolecular rate constant 6times;106cm3moleminus;1sdot;secminus;1), in disagreement with other reported results.
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