Reflected Shock Tube Studies of High-Temperature Rate Constants for OH + CH4 → CH3 + H2O and CH3 + NO2 → CH3O + NO

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 109; no. 9; pp. 1857 - 1863
• Main Authors: Srinivasan, N. K, Su, M.-C, Sutherland, J. W, Michael, J. V
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 10-03-2005
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp040679j

The reflected shock tube technique with multipass absorption spectrometric detection of OH radicals at 308 nm has been used to study the reactions OH + CH4 → CH3 + H2O and CH3 + NO2 → CH3O + NO. Over the temperature range 840−2025 K, the rate constants for the first reaction can be represented by the Arrhenius expression k = (9.52 ± 1.62) × 10-11 exp[(−4134 ± 222 K)/T] cm3 molecule-1 s-1. Since this reaction is important in both combustion and atmospheric chemistry, there have been many prior investigations with a variety of techniques. The present results extend the temperature range by 500 K and have been combined with the most accurate earlier studies to derive an evaluation over the extended temperature range 195−2025 K. A three-parameter expression describes the rate behavior over this temperature range, k = (1.66 × 10-18)T 2.182 exp[(−1231 K)/T] cm3 molecule-1 s-1. Previous theoretical studies are discussed, and the present evaluation is compared to earlier theoretical estimates. Since CH3 radicals are a product of the reaction and could cause secondary perturbations in rate constant determinations, the second reaction was studied by OH radical production from the fast reactions CH3O → CH2O + H and H + NO2 → OH + NO. The measured rate constant is 2.26 × 10-11 cm3 molecule-1 s-1 and is not dependent on temperature from 233 to 1700 K within experimental error.