Temperature Dependence Kinetic Studies of the Reaction of O( 3 P) with CHI 3 and C 2 H 5 I and the 298 K Reaction of OH(X 2 Π) with CHI 3

A flash photolysis–resonance fluorescence technique was used to investigate the kinetics of the OH(X 2 Π) radical and O( 3 P) atom‐initiated reactions with CHI 3 and the kinetics of the O( 3 P) atom‐initiated reaction with C 2 H 5 I. The reactions of the O( 3 P) atom with CHI 3 and C 2 H 5 I were studied over the temperature range of 296 to 373 K in 14 Torr of helium, and the reaction of the OH (X 2 Π) radical with CHI 3 was studied at T = 298 K in 186 Torr of helium. The experiments involved time‐resolved resonance fluorescence detection of OH (A 2 Σ + → X 2 Π transition at λ = 308 nm) and of O( 3 P) (λ = 130.2, 130.5, and 130.6 nm) following flash photolysis of the H 2 O/He, H 2 O/CHI 3 /He, O 3 /He, and O 3 /C 2 H 5 I/He mixtures. A xenon vacuum UV (VUV) flash lamp (λ > 120 nm) served as a photolysis light source. The OH radicals were produced by the VUV flash photolysis of water, and the O( 3 P) atoms were produced by the VUV flash photolysis of ozone. Decays of OH radicals and O( 3 P) atoms in the presence of CHI 3 and C 2 H 5 I were observed to be exponential, and the decay rates were found to be linearly dependent on the CHI 3 and C 2 H 5 I concentrations. Measured rate coefficients for the reaction of O( 3 P) atoms with CHI 3 and C 2 H 5 I are described by the following Arrhenius expressions (units are cm 3 s −1 ): k O+C2H5I ( T ) = (17.2 ± 7.4) × 10 −12 exp[−(190 ± 140)K/ T ] and k O+CHI3 ( T ) = (1.80 ± 2.70) × 10 −12 exp[−(440 ± 500)K/ T ]; the 298 K rate coefficient for the reaction of the OH radical with CHI 3 is k OH+CHI3 (298 K) = (1.65 ± 0.06) × 10 −11 cm 3 s −1 . The listed uncertainty values of the Arrhenius parameters are 2σ‐standard errors of the calculated slopes by linear regression.