RATE CONSTANTS FOR THE REACTIONS OF C2H5, C2H5O AND C2H5O2 RADICALS WITH NO3 AT 298 K AND 2.2 TORR

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, O-2 and NO2 for reaction (3). Reactions (2) and (3) are therefore highly coupled and, in order to determine the rate constants k(2) and k(3) 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: k(1) = (4.0 +/- 1.0) x 10(-11) cm(3) molecule(-1) s(-1), k(2) = (3.5 +/- 1.0) x 10(-12) cm(3) molecule(-1) s(-1) and k(3) = (2.5 +/- 1.5) x 10(-12) cm(3) 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.