Atmospheric fate of several alkyl nitrates Part 1Rate coefficients of the reactions of alkyl nitrates with isotopically labelled hydroxyl radicals

Abstract

The rate coefficients for the reaction of OH radical with CH ₃ ONO ₂ (k ₁ ), CD ₃ ONO ₂ (k ₆ ), C ₂ H ₅ ONO ₂ (k ₂ ) and 2-C ₃ H ₇ ONO ₂ (k ₃ ) between 220 and 410 K were measured to be: k ₁ =(8.2±1.6)×10 ^-13 exp{-(1020±60)/T}, k ₆ =(1.6±0.2)×10 ^-12 exp{-(1730±40)/T}, k ₂ =3.68×10 ^-12 exp(-1077/T)+5.32×10 ^-14 exp(126/T) and k ₃ =4.3×10 ^-12 exp(-1250/T)+2.5×10 ^-13 exp(-32/T) cm ³ molecule ^-1 s ^-1 . The quoted errors in the Arrhenius expressions are at the 95% confidence limit and include estimated systematic errors. The measured rate coefficients for the reactions of ¹⁸ OH were roughly the same as those for ¹⁶ OH reactions while the rate constants for OD reactions were slightly (ca. 10–15%) higher than those for OH reactions. The hydroxyl radicals were generated by pulsed laser photolysis and detected by pulsed laser induced fluorescence. The observed large primary kinetic isotope effect (k ₁ /k ₆ =4.5 at 298 K), the independence of the measured rate coefficients on the gas composition, and the trend in the reactivity with the alkyl group suggests that the above reactions proceed via abstraction of an H atom from the alkyl group. Our results are compared with those from previous studies.