Quantum chemical and kinetic study of the reaction between CCl₂ and NO₂ radicals

The dependence of the rate constant of the recombination reaction of CCl₂ and NO₂ radicals on temperature and pressure was studied. Quantum-chemical calculations were employed to characterize relevant aspects of the potential energy surface for this process. The limiting rate constants between 300 and 2000 K were analyzed using the unimolecular reactions theory. The resulting low pressure rate constant can be represented as k₀ = [He] (1.4 ± 0.2) × 10^-26 (T/300 K)^-8.72±0.04 exp(-(1520 ± 10) K/T) cm³ molecule^-1 s^-1. The corresponding expressions for the high pressure limit rate constants, derived from a simplified version of the statistical adiabatic channel (SSACM) and from a SACM combined with classical trajectory calculations (SACM/CT), are (2.3 ± 1.9) × 10^-11 (T/300 K)^-1.01±0.39 exp(-(810 ± 80) K/T) and (8.8 ± 5.3) × 10^-13 (T/300 K)^0.82±0.13 cm³ molecule^-1 s^-1. The falloff curves were represented in terms of these limiting rate constants. Reported experimental results are well described with the present model. Our calculations indicate that the CCl₂ + NO₂ reaction proceeds via the stabilization of the energized CCl₂NO₂ adduct, and that the CCl₂ + NO₂ → CCl₂O + NO channel becomes relevant at high temperatures.