Temperature Dependence Kinetic Studies of the Reaction of O(3P) with CHI3 and C2H5I and the 298 K Reaction of OH(X2Π) with CHI3

Abstract

ABSTRACTA flash photolysis–resonance fluorescence technique was used to investigate the kinetics of the OH(X2Π) radical and O(3P) atom‐initiated reactions with CHI3 and the kinetics of the O(3P) atom‐initiated reaction with C2H5I. The reactions of the O(3P) atom with CHI3 and C2H5I were studied over the temperature range of 296 to 373 K in 14 Torr of helium, and the reaction of the OH (X2Π) radical with CHI3 was studied at T = 298 K in 186 Torr of helium. The experiments involved time‐resolved resonance fluorescence detection of OH (A2Σ+ → X2Π transition at λ = 308 nm) and of O(3P) (λ = 130.2, 130.5, and 130.6 nm) following flash photolysis of the H2O/He, H2O/CHI3/He, O3/He, and O3/C2H5I/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(3P) atoms were produced by the VUV flash photolysis of ozone. Decays of OH radicals and O(3P) atoms in the presence of CHI3 and C2H5I were observed to be exponential, and the decay rates were found to be linearly dependent on the CHI3 and C2H5I concentrations. Measured rate coefficients for the reaction of O(3P) atoms with CHI3 and C2H5I are described by the following Arrhenius expressions (units are cm3 s−1): kO+C2H5I(T) = (17.2 ± 7.4) × 10−12 exp[−(190 ± 140)K/T] and kO+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 CHI3 is kOH+CHI3(298 K) = (1.65 ± 0.06) × 10−11 cm3 s−1. The listed uncertainty values of the Arrhenius parameters are 2σ‐standard errors of the calculated slopes by linear regression.