Temperature-Dependent Kinetics of the Gas-Phase Reactions of OH with Cl₂, CH₄, and C₃H₈

Abstract

The reactions of OH with molecular chlorine (reaction 1), methane (reaction 2), and propane (reaction 3) have been studied experimentally using a pulsed laser photolysis/pulsed-laser-induced fluorescence technique over wide ranges of temperatures (297-826, 298-1009, and 296-908 K, respectively) and at pressures between 6.68 and 24.15 kPa. The rate coefficients obtained for reactions 1-3 demonstrate no dependence on pressure and exhibit positive temperature dependences that can be represented with modified three-parameter Arrhenius expressions within their corresponding experimental temperature ranges: k 1 ) 3.59 × 10 -16 T 1.35 exp(-745 K/T) cm 3 molecule -1 s -1 , k 2 ) 3.82 × 10 -19 T 2.38 exp(-1136 K/T) cm 3 molecule -1 s -1 , and k 3 ) 6.64 × 10 -16 T 1.46 exp(-271 K/T) cm 3 molecule -1 s -1 . For the OH + Cl 2 reaction, the potential energy surface has been studied using quantum chemical methods, and a transition-state theory model has been developed on the basis of calculations and experimental data. Model predictions suggest OH + Cl 2 f HOCl + Cl as the main channel of this reaction. The model results in the expression k 1 ) 1.35 × 10 -16 T 1.50 exp(-723 K/T) cm 3 molecule -1 s -1 for the temperature dependence of the reaction 1 rate coefficient extrapolation outside the experimental range to low temperatures down to 200 K and to high temperatures up to 3000 K. A temperature dependence of the rate coefficient of the HOCl + Cl f OH + Cl 2 reaction has been derived on the basis of the experimental data, modeling, and thermochemical information.

Pathways for the OH + Cl2 → HOCl + Cl and HOCl + Cl → HCl + ClO Reactions

“…11 However, the exit complex A predicted here by the CCSD(T) method is intermediate between the TSA and TSB structures predicted by the BH&HLYP/aug-cc-pVDZ DFT method. 10 No other intermediate product is found in the reactant valley for the reaction HOCl + Cl.…”

Kinetic Study of the Gas-Phase Reaction of OH with Br2

“…10 The evaluation of potential systematic errors was mainly based on the finite accuracies stated by the manufacturers for the devices used in our experiments. The uncertainties in the measured experimental parameters were propagated to the final values of the uncertainties in the measured rate coefficients, using different mathematical procedures for propagating systematic and statistical uncertainties.…”

“…The experimental set-up has been described in detail in our previous article 10 and is considered here only briefly.…”

Carbon and hydrogen isotope fractionation associated with the aerobic microbial oxidation of methane, ethane, propane and butane

“…While alkanes are among the least chemically reactive organic compounds, C3 and C4 contain C-H bonds at the secondary position (at the non-terminal carbon site) which are more reactive than C-H bonds at the primary position (e.g., C1 and C2). In non-biological reactions, such as gas phase reactions of alkanes with OH, the C3 reaction is approximately 175 times faster than the C1 reaction at 25°C (Bryukov et al, 2004).…”