RATE CONSTANTS OF THE REACTIONS OF CF3O2, I-C3H7O2 AND T-C4H9O2 WITH NO

The kinetics of the title reactions have been studied at T = 290 K and p = 2 Torr He using the fast-flow technique combined with molecular-beam sampling mass spectrometry. - In our novel approach, the total rate constant k1 of RO2 + NO --> RO + NO2/RONO2 (1) is determined from the shape of the NO2-growth profile. The validity of the method is demonstrated by the nearly identical results for k1 (CF3O2 + NO) obtained from CF3O2-decays: k1 = (1.54 +/- 0.35) . 10(-11) and from NO2-growths: k1 = (1.51 +/- 0.4) . 10(-11) cm3 s-1, in excellent agreement also with previous determinations. - Rate coefficient data of alkylperoxy + NO reactions, derived from NO2-profiles, are reported for i-C3H7O2 + NO: k1 = (5.0 +/- 1.2) . 10(-12) and for t-C4H9O2 + NO: k1 = (4.0 +/- 1.1) . 10(-12) cm3 s-1. Our results, in combination with literature values for smaller peroxy radicals, indicate a marked decrease of the rate coefficient with increasing CH3-substitution. Including data on haloalkyl- and acetylperoxy reactions, the reactivity of RO2 towards NO is shown to correlate with the electron acceptor/donor properties of substituents on the alpha-carbon.