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

A 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.

Atmospheric chemistry of alkyl iodides: theoretical studies on the mechanisms and kinetics of CH3I/C2H5I + NO3reactions

“…Similar theoretical results can be also found in the reaction of C 2 H 5 I with a Cl atom 45 and for other alkyl iodides reactions with O( 3 P) and OH radicals. 19,47,48 Fig. 4a and b show the temperature dependence of the branching ratios for the reactions of CH 3 I and C 2 H 5 I with a NO 3 radical, respectively.…”

“…17 In the last few years, attention has focused on the NO 3 nighttime reactivity in urban zones with a series of hydrogen compounds. [18][19][20][21][22] Herein, we focus on the important iodine cycle reactions, namely CH 3 I and C 2 H 5 I with NO 3 radicals. The reactions can proceed via seven reaction channels, including Habstraction ((R1a, R2a), (R1b), (R2b and R3b)) and displacement ((R3a) and (R4b)), e.g., The reactions of NO 3 with CH 3 I and C 2 H 5 I were reported by Nakano et al 9,12 through the cavity ring-down spectroscopy method.…”

Important effects of relative humidity on the formation processes of iodine oxide particles from CH3I photo-oxidation

“…The gas phase CH 3 I was introduced into the chamber using the gas saturation method first developed by Regnault in 1845 [35]; one of the oldest and most versatile ways of studying gasliquid equilibria involving low vapor pressure compounds. Further, the gas saturation method used in this work is similar to the one employed in a number of other studies of atmospheric interest [36,37,38,39] where precise reactant concentrations of volatile or semi-volatile compounds needed to be known. Its operation principle and the calculation of the concentration of CH 3 I leaving the saturation system have been presented in detail elsewhere [40].…”

Theoretical Study of the Hydroxyl‐Radical‐Initiated Degradation Mechanism, Kinetics, and Subsequent Evolution of Methyl and Ethyl Iodides in the Atmosphere

“…Subsequently, Zhang et al [19] widened the reaction temperature interval to T = 297-372 K and explored the temperature-dependent effects of the rate coefficients. In addition, Zhang et al [23] measured the kinetic parameters of the reactions of * OH and O( 3 P) atoms with CHI 3 and C 2 H 5 I in the temperature range T = 296-373 K using flash photolysis resonance fluorescence technique. A theoretical study was reported by Marshall et al [24] on the H-abstraction and I-abstraction pathways for the reaction of CH 3 I with * OH at the MP2/6-31G(d) level and found that the H-abstraction reaction outperformed the I-abstraction reaction.…”