Rate constants for the gas-phase reactions of NO ₃ radicals and O ₃ with C ₆ - C ₁₄ 1-alkenes and 2-methyl-1-alkenes at 296 ± 2 K

Rate constants for the gas-phase reactions of NO ₃ radicals and O ₃ with a series of C ₆-C ₁₄ 1-alkenes and 2-methyl-1-alkenes have been measured at 296 ± 2 K and atmospheric pressure of air using relative rate methods. For the NO ₃ radical reactions, the rate constants obtained (in units of 1(T ^-14 cm ³ molecule ^-1 s ^-1) were: 1-hexene, 2.00 ± 0.16; 1-octene, 2.35 ± 0.15; 1-decene, 2.55 ± 0.16; 1-dodecene, 2.79 ± 0.36; 1-tetradecene, 2.87 ± 0.21; 2-methyl-1-pentene, 43.8 ± 2.3; 2-methyl-1-hexene, 52.4 ± 2.5; 2-methyl-1-octene, 57.8 ± 2.6; 2-methyl-1-nonene, 60.8 ± 2.9; 2-methyl-1-undecene, 60.8 ± 3.3; 2-methyl-1-tridecene, 60.3 ± 3.4; and cycloheptene, 49.4 ± 2.0. For the O ₃ reactions, the rate constants obtained (in units of 10 ^-17 cm ³ molecule ^-1 s ^-1) were: 1-hexene, 0.898 ± 0.054; 1-heptene, 1.05 ± 0.07; 1-octene, 1.01 ± 0.04; 1-decene, 1.11 ± 0.05; 1-dodecene, 1.38 ± 0.14; 1-tridecene, 1.92 ± 0.12; 1-tetradecene, 2.44 ± 0.24; 2-methyl-1-pentene, 1.26 ± 0.13; 2-methyl-1-heptene, 1.35 ± 0.05; 2-methyl-1-octene, 1.38 ± 0.06; 2-methyl-1-decene, 1.48 ± 0.07; 2-methyl-1-undecene, 1.46 ± 0.11; and 2-methyl-1-tridecene, 2.85 ± 0.42. The rate constants for the NO ₃ radical reactions significantly increase with increasing carbon number, attaining a plateau at ≥C ₁₄ for the 1-alkenes and at C ₁₀ - C ₁₄ for the 2-methyl-1-alkenes. In contrast, the rate constants for O ₃ reactions increase only slightly with increasing carbon number up to ∼C ₁₀ for the 1-alkenes and ∼C ₁₂ for the 2-methyl-1-alkenes, with the significant increase in the measured rate constants for the >C ₁₀ 1-alkenes and >C ₁₂ 2-methyl-1-alkenes possibly being due to heterogeneous reactions. Reasons for the observed trends in NO ₃ radical and O ₃ reaction rate constants with alkene carbon number are discussed.