High Temperature Reaction of S + SO₂ → SO + SO: Implication of S₂O₂ Intermediate Complex Formation

The rate constant for the reaction S + SO₂ → SO + SO (1) has been investigated by measuring time profiles of S atoms behind reflected shock waves using two experimental systems: S atoms were provided by the thermal decomposition of COS in the high-temperature range (2020-2800 K) and by excimer laser photolysis of COS in the low-temperature range (T = 1120-1540 K). The results of these experiments yield the rate constant with a non-Arrhenus temperature dependence, k₁ = 10^-39.73T^8.21 exp(4828.5/T) cm³ molecules^-1 s^-1, over the extended temperature range (1120-2800 K). By comparing the rate constants with that derived from a conventional transition-state theory based on the potential energy surface calculated by the G2M-(CC1) methodology, a reaction mechanism including a contribution of the singlet state of the reaction intermediate S₂O₂ is discussed.