Rate constants for the reactions of C2H5, C2H5O and C2H5O2 radicals with NO3 at 298 K and 2.2 torr

Abstract

A discharge-flow system equipped with a laser-induced fluorescence cell to detect the ethoxyl radical and an optical absorption cell to detect the nitrate radical has been used to measure the rate constants for the reactions C₂H₅+ NO₃→ products (1), C₂H₅O + NO₃→ products (2), C₂H₅O₂+ NO₃→ products (3), at T= 298 K and P= 2.2 Torr. The major products of these reactions are C₂H₅O and NO₂ for reaction (1), C₂H₅O₂ and NO₂ for reaction (2) and C₂H₅O, O₂ and NO₂ for reaction (3). Reactions (2) and (3) are therefore highly coupled and, in order to determine the rate constants k₂ and k₃ for these reactions, two types of experiment were performed. In the first set of experiments, C₂H₅O was generated in situ via reaction (1) and allowed to react with NO₃ and, in the second set of experiments, C₂H₅O₂ was generated separately and allowed to react with NO₃. A numerical model was then used to derive the following rate constants : k₁=(4.0 ± 1.0)× 10^–11 cm³ molecule^–1 s^–1, k₂=(3.5 ± 1.0)× 10^–12 cm³ molecule^–1 s^–1 and k₃=(2.5 ± 1.5)× 10^–12 cm³ molecule^–1 s^–1. The errors quoted are not statistically derived, but rather represent ranges over which the numerical simulations fit the experimental data adequately. The mechanisms for reactions (1) and (2) are discussed in terms of the QRRK treatment and the atmospheric implications of reaction (3) are considered.