KINETIC INVESTIGATION OF THE REACTIONS OF NCO RADICALS WITH ALKANES IN THE TEMPERATURE-RANGE 294-K TO 1113-K

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(1) Delta) + HNCO --> NH2 + NCO, following the 193-nm photolysis of isocyanic acid. The measured rate coefficients can be described by the following expressions: k(1)(512 < T < 1113 K) = 10(12.99+/-0.12) x exp(-34.0 +/- 1.8 kJ mol(-1)/RT) cm(3) mol(-1) s(-1), (1) k(2)(296 < T < 922 K) = 10(8.21) x (T/298 K)((6.89+/-0.02)) x exp(12.2 +/- 0.5 kJ mol(-1)/RT) cm(3) mol(-1) s(-1), (2) k(3)(300 < T < 849 K) = 10(11.49) x (T/298 K)((2.15+/-0.02)) x exp(-1.8 +/- 0.4 kJ mol(-1)/RT) cm(3) mol(-1) s(-1). (3) 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.