Kinetic study of the reaction of OH with CH2I2

Abstract

Flash photolysis (FP) coupled to resonance fluorescence (RF) was used to measure the absolute rate coefficients (k₁) for the reaction of OH(X²Π) radicals with diiodomethane (CH₂I₂) over the temperature range 295–374 K. The experiments involved time-resolved RF detection of the OH (A²Σ⁺ → X²Π transition at λ = 308 nm) following FP of the H₂O/CH₂I₂/He mixtures. The OH(X²Π) radicals were produced by FP of H₂O in the vacuum-UV at wavelengths λ > 120 nm. Decays of OH radicals in the presence of CH₂I₂ are observed to be exponential, and the decay rates are found to be linearly dependent on the CH₂I₂ concentration. The results are described by the Arrhenius expression k₁(T) = (4.2 ± 0.5) × 10⁻¹¹ exp[−(670 ± 20)K/T] cm³ molecule⁻¹ s⁻¹. The implications of the reported kinetic results for understanding the atmospheric chemistry of CH₂I₂ are discussed.