Reactivity of the nitrate radical towards alkynes and some other molecules

Abstract

A time-resolved flow method has been used to obtain absolute rate constants (in units of 10¹⁶ cm³ molecule^–1 s^–1) for the reaction of the nitrate radical with acetylene (0.51 ± 0.35), propyne (2.66 ± 0.32), but-1-yne (4.55 ± 0.45), but-2-yne ( 670 ± 150), pent-1-yne (7.54 ± 0.75), hex-1-yne (16.0 ± 1.9), ethylene (1.85 ± 0.24), isobutene (3400 ± 700) and buta-1,3-diene (2200 ± 600). The possible influences of secondary reactions are considered and it is concluded that only in the cases of but-2-yne and buta-1, 3-diene are secondary process likely to interfere with the calculation of rate constants. For these two species, therefore, the rate constants above must be taken as upper limits, although it is improbable that the values are grossly high. The nitrate radical was generated by the reaction F + HNO₃→ HF + NO₃(1), and an absolute kinetic method was used. Upper limits of 1 × 10^–17 cm³ molecule^–1 s^–1 were measured for the coefficients of any interactions of NO₃ with SO₂ and O₂. The rate of the reaction NO₂+ NO₃+ M → N₂O₅+ M (2) was measured in the range 2–8 Torr and good agreement with literature values for the pressure dependence (M = He) was obtained. Comparisons with rate constants for the corresponding reaction rates with OH, O(³P) and O₃ were made.