Investigation into the pressure dependence between 1 and 10 Torr of the reactions of NO2 with CH3 and CH3O

Abstract

The kinetics and pressure dependence of the reactions of NO₂ with CH₃ and CH₃O have been investigated in the gas phase at 298 K, at pressures from 1 to 10 Torr. A low-pressure discharge-flow laser-induced fluorescence (LIF) technique was used. In a consecutive process, CH₃ reacted with NO₂ to form CH₃O, CH₃+ NO₂→ CH₃O + NO (1), which further reacted with NO₂ to form products, CH₃O + NO₂→ products (2). Reaction (1) displayed no discernible pressure dependence over the pressure range 1–7 Torr, and k₁ was calculated to be (2.3 ± 0.3)× 10^–11 cm³ molecule^–1 s^–1. Reaction (2) displayed a strong pressure dependence and an RRKM analysis yielded the following limiting low- and high-pressure rate constants in He, k₀= 5.9 × 10^–29 cm⁶ molecule^–2 s^–1 and k_∞= 2.1 × 10^–11 cm³ molecule^–1 s^–1. It is unrealistic to quote errors for this type of analysis. Parametrisation in the standard Troe form with F_c= 0.6 yielded k₀=(5.3 ± 0.2)× 10^–29 cm⁶ molecule^–2 s^–1 and k_∞=(1.4 ± 0.1)× 10^–11 cm³ molecule^–1 s^–1. Atmospheric implications and possible reaction mechanisms are discussed.