Reactions of Cl atoms with CH3I, C2H5I, 1-C3H7I, 2-C3H7I and CF3I: kinetics and atmospheric relevance

Abstract

The kinetics of the reactions

were studied at T = 298 K using a fast-flow discharge system with resonance-fluorescence detection of Cl atoms. The rate coefficients were found to be pressure-independent over the range 1.5–12 Torr, and were k₁ = (1.51 ± 0.15) × 10⁻¹² cm³ molecule⁻¹ s⁻¹, k₂ = (16.0 ± 1.7) × 10⁻¹² cm³ molecule⁻¹ s⁻¹, k₃ = (66.5 ± 7.5) × 10⁻¹² cm³ molecule⁻¹ s⁻¹, k₄ = (46.8 ± 4.9) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ and k₅ = (0.85 ± 0.09) × 10⁻¹² cm³ molecule⁻¹ s⁻¹. The rates of reaction of these alkyl iodides with Cl atoms in the marine boundary layer were compared with the rates of their photolysis and their reaction with OH. For early morning conditions, it is shown that reaction with Cl atoms can compete with photolysis and dominate over reaction with OH, if Cl atom concentrations are about 1 × 10⁵ molecule cm⁻³. Atomic iodine may be released following reaction of Cl with the alkyl iodides; this atomic I can participate in catalytic destruction of ozone in the marine boundary layer.