Ab initio studies of ClO_x reactions. 2. Unimolecular decomposition of s-ClO₃ and the bimolecular O + OClO reaction

The unimolecular decomposition of symmetric ClO₃ has been investigated at the G2M(CC2)//PW91PW91/ 6-311+G(3df) level of theory. The results Show that the main dissociation products are ³O + OClO instead of the commonly assumed ClO + O₂. The rate constants at high- and low-pressure limits were predicted to be k₂^∞ = 1.5 × 10²⁰T^-1.1 exp(-18360/T) s^-1 and k₂⁰ = 3.76 × 10²⁵T^-3.28 exp(-13890/T) cm³ mol^-1 s^-1 in the temperature range 500-2500 K. For the bimolecular processes, the sum of the predicted abstraction (k₃) and association (k_-2) values can reasonably explain the experimental nonzero intercepts of the strong pressure-dependent rate constants, with the predicted total rate constants agreeing closely with the experimental values. The association and abstraction rate constants in the temperature range 200-500 K can be represented respectively by k_-2 = 40.1T^-6.16 exp(-403/T) for 1 Torr He and k₃ = 1.0 × 10^-16T^1.44 exp(-469/T) cm³ molecule^-1 s^-1. The abstraction rate constant for 500-2500 K can be expressed by k₃ = 8.69 × 10^-17T^1.45 exp(-441/T) cm³ molecule^-1 s^-1.