Kinetics of the Reactions of Ozone with Halogen Atoms in the Stratosphere

Abstract

It is well established that reaction cycles involving inorganic halogens contribute to the depletion of ozone in the atmosphere. Here, the kinetics of O₃ with halogen atoms (Cl, Br, and I) were investigated between 180 and 400 K, expanding the temperature range relative to prior studies. Canonical variational transition state theory including small curvature tunneling correction (CVT/SCT) were considered, following the construction of the potential energy surfaces. MRCI + Q/aug-ano-pVTZ//MP2/aug-cc-pV(T + d)Z and MRCI + Q/aug-ano-RCC-VTZP//MP2/aug-cc-pV(T + d)Z levels of theory were used to calculate the kinetic parameters. Calculated rate coefficients were used to fit the Arrhenius equations, which are obtained to be k₁ = (3.48 ± 0.4) × 10⁻¹¹ exp[(−301 ± 64)/T] cm³ molecule⁻¹ s⁻¹, k₂ = (3.54 ± 0.2) × 10⁻¹¹ exp[(−990 ± 35)/T] cm³ molecule⁻¹ s⁻¹ and k₃ = (1.47 ± 0.1) × 10⁻¹¹ exp[(−720 ± 42)/T] cm³ molecule⁻¹ s⁻¹ for the reactions of O₃ with Cl, Br, and I atoms, respectively. The obtained rate coefficients for the reactions of O₃ with halogen atoms using CVT/SCT are compared to the latest recommended rate coefficients by the NASA/JPL and IUPAC evaluations. The reactivity trends and pathways of these reactions are discussed.