Rate Coefficients for the OH + CF₃I Reaction between 271 and 370 K

Abstract

The rate coefficient, k 1, for the reaction OH + CF3I → products was measured under pseudo-first-order conditions in hydroxyl radical, OH. OH temporal profiles were monitored by laser-induced fluorescence (LIF), and CF3I concentrations were determined by UV/Visible absorption. We determined k 1 (T) to be (2.10 ± 0.80) × 10-11 exp[−(2000 ± 140)/T] cm3 molecule-1 s-1, over the temperature range 271 to 370 K. The quoted uncertainties are 2σ (95% confidence limits, σA = AσlnA). Previous measurements of k 1(T) are compared with our values, and possible reasons for the discrepancies are discussed. The heat of formation of HOI is deduced to be less than −16 kcal mole-1, if the products of reaction 1 are mostly HOI and CF3. These measurements support the earlier conclusion that the reaction of OH with CF3I plays a negligibly small role in the atmospheric removal of CF3I.

Potential impacts of CF<sub>3</sub>I on ozone as a replacement for CF<sub>3</sub>Br in aircraft applications

“…Other chemical pathways of CF 3 I degradation, such as reactions with O and OH, could further decrease its lifetime. The newest kinetics study on the reaction of CF 3 I with OH has been carried out by Gilles et al (2000). Their results showed a very small rate coefficient value and a negligible role in the atmospheric removal of CF 3 I.…”

“…As a consequence, these results may have been inaccurate in estimating the impact of iodine on the ozone depletion. Recently, numerous kinetic studies on iodine compounds have been carried out and the understanding of iodine chemistry has improved considerably (e.g., Turnipseed et al, 1997;Gilles et al, 2000). As a result, in this study, we have attempted to reevaluate the role of iodine chemicals on the ozone depletion using the updated evaluations of iodine chemistry.…”

Determination of Atmospheric Lifetimes via the Measurement of OH Radical Kinetics

“…410−450 nm) using a dye laser pumped by the third harmonic of a Nd:YAG laser: The use of different sources of OH allows one to examine any effects of the hydroxyl source on the derived OH rate constant. These different OH generation methods also allow the use of longer wavelength radiation, which generally results in less photolysis of the reactants, , although such use can complicate chemistry in the reacting mixture because of the reaction between OH and its precursors. Thus, extreme care must be taken to ensure that the measured OH rate constants are not affected by complications due to reactant photolysis or OH reactions with its precursors.…”

Measurement of the rate constants of the reactions of the chlorine atom with C3F7I and CF3I using the resonance fluorescence of chlorine atoms

“…The value of the rate constant of reaction (III) obtained by us is between the values measured ear lier (8.5 × 10 -13 cm 3 molecule -1 s -1 [32] and 5.1 × 10 -13 cm 3 molecule -1 s -1 [31]). Although the rate constant of the reaction of the chlorine atom with CF 3 I is almost 30 times larger than the rate constant of the reaction of the OH • radical with the same refriger ant [34], neither process can compete with the photol ysis of CF 3 I in the troposphere. We attempted to detect iodine atoms as a reaction product by the resonance fluorescence method.…”