Investigation into the kinetics and mechanism of the reaction of NO3 with CH3 and CH3O at 298 K between 0.6 and 8.5 Torr: is there a chain decomposition mechanism in operation?

Abstract

The reactions CH₃+ NO₃→ products (1), and CH₃O + NO₃→ products (2), have been studied using a flow system at T= 298 K and at pressures between 0.6 and 8.5 Torr. The laser-induced fluorescence (LIF) technique was used to detect CH₃O and multi-pass optical absorption to detect NO₃. The chemical systems were studied as a pair of consecutive reactions; however, a simple analytical treatment was not sufficient to describe them because CH₃O₂ was formed as one of the products in the major channel of reaction (2). This species also reacts with NO₃ regenerating CH₃O. Use of a numerical model to correct for this regeneration process allowed rate parameters of k₁=(3.5 ± 1.0)× 10^–11 cm³ molecule^–1 s^–1 and k₂=(2.3 ± 0.7)× 10^–12 cm³ molecule^–1 s^–1 to be determined at 2.4 Torr. There is no pressure dependence observed for reaction (1) between 1 and 2.4 Torr, but the possibility of a slight pressure dependence for reaction (2) exists. These pressure effects are examined using the semi-empirical quantum RRK method.