Rate coefficients for the reaction of OH with (E)-2-pentenal, (E)-2-hexenal, and (E)-2-heptenal

Abstract

Rate coefficients for the gas-phase reaction of the OH radical with (E)-2-pentenal (CH₃CH₂CHCHCHO), (E)-2-hexenal (CH₃(CH₂)₂CHCHCHO), and (E)-2-heptenal (CH₃(CH₂)₃CHCHCHO), a series of unsaturated aldehydes, over the temperature range 244–374 K at pressures between 23 and 150 Torr (He, N₂) are reported. Rate coefficients were measured under pseudo-first-order conditions in OH with OH radicals produced via pulsed laser photolysis of HNO₃ or H₂O₂ at 248 nm and detected by pulsed laser-induced fluorescence. The rate coefficients were independent of pressure and the room temperature rate coefficients and Arrhenius expressions obtained are (cm³ molecule⁻¹ s⁻¹ units): k₁(297 K) = (4.3 ± 0.6) × 10⁻¹¹, k₁(T) = (7.9 ± 1.2) × 10⁻¹² exp[(510 ± 20)/T]; k₂(297 K) = (4.4 ± 0.5) × 10⁻¹¹, k₂(T) = (7.5 ± 1.1) × 10⁻¹² exp[(520 ± 30)/T]; and k₃(297 K) = (4.4 ± 0.7) × 10⁻¹¹, k₃(T) = (9.7 ± 1.5) × 10⁻¹² exp[(450 ± 20)/T] for (E)-2-pentenal, (E)-2-hexenal and (E)-2-heptenal, respectively. The quoted uncertainties are 2σ (95% confidence level) and include estimated systematic errors. Rate coefficients are compared with previously published room temperature values and the discrepancies are discussed. The atmospheric degradation of unsaturated aldehydes is also discussed.