Temperature-dependent kinetics of the gas-phase reactions of OH with Cl 2, CH 4, and C 3H 8

Document Type

Article

Publication Date

11-25-2004

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 → 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 → OH + Cl 2 reaction has been derived on the basis of the experimental data, modeling, and thermochemical information.

Publication Source (Journal or Book title)

Journal of Physical Chemistry A

First Page

10464

Last Page

10472

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