Kinetic investigation of the reactions of NCO radicals with alkanes in the temperature range 294 to 1113 K

Abstract

Absolute rate coefficients for the reaction of NCO radicals with methane ( k 1), ethane ( k 2), and propane ( k 3) were measured as a function of temperature in a heatable quartz reactor by means of the laser photolysis/laser-induced fluorescence (LP/LIF) pump-probe technique. NCO radicals were produced by the fast precursor reaction NH( a 1Δ) +HNCO → NH 2 + NCO, following the 193-nm photolysis of isocyanic acid. The measured rate coefficients can be described by the following expressions: (1) k 1 ( 512 < T < 1113 K ) = 10 12.99 ± 0.12 × exp ⁡ ( − 34.0 ± 1.8 k J mol − 1 / R T ) c m 3 mol − 1 s − 1 , (2) k 1 ( 296 < T < 922 K ) = 10 8.21 × ( T / 298 K ) ( 6.89 ± 0.02 ) × exp ⁡ ( 12.2 ± 0.5 k J mol − 1 / R T ) c m 3 mol − 1 s − 1 , (3) k 3 ( 300 < T < 849 K ) = 10 11.49 × ( T / 298 K ) ( 2.15 ± 0.02 ) × exp ⁡ ( − 1.8 ± 0.4 k J mol − 1 / R T ) c m 3 mol − 1 s − 1 A comparison with the corresponding reactions of CN, Cl, and OH radicals with alkanes suggests that all these title reactions also proceed predominantly via a hydrogen atom abstraction mechanism to form HNCO.