Rate of the reaction O+SO2+M→SO3+M

The rate of the reaction O+SO2+M→SO3+M has been measured under pseudo-first-order conditions in a discharge flow reactor with ESR detection. For M=He at room temperature, extensive measurements over a wide SO2 mole fraction range were used to evaluate the rate constant for both He (k1) and SO2 (k2) as third bodies. The results were k1=3.0±0.2×1014 cm6 mole−2⋅ sec−1 and k2/k1=9.5±2.7, the error limits being simply experimental mean deviations. Similar experiments for M=N2 (k4) at room temperature yielded k4=7.2±0.3×1014. Measurements of M=He over the temperature range 248–415 °K gave the Arrhenius result k1=3.9±0.9×1016 exp[−(1400±50)/T]. The positive Arrhenius activation energy is in good agreement with other published results, and some discussion of this unusual feature for termolecular reactions is presented.