Absolute Rate Coefficient of the HCCO + NO Reaction over the Range T = 297−802 K

Abstract

The absolute rate coefficient of the gas-phase reaction HCCO + NO was experimentally determined for the first time over an extended temperature range, 297−802 K. HCCO radicals were generated by pulsed-laser photolysis of CH2CO at 193 nm. Their subsequent decay, under pseudo-first-order conditions, was monitored in real time using a newly developed laser-photofragment/laser-induced fluorescence technique (Carl, S. A.; Sun, Q.; Peeters, J. J. Chem. Phys. 2000, 114, 10332) that involved pulsed-laser photodissociation of HCCO at 266 nm and laser-induced fluorescence at ca. 430 nm of the resulting nascent rotationally excited CH(X2Π) photofragment. The rate coefficient of the title reaction was found to exhibit a negative temperature dependence described by k5(T)(HCCO+NO) = (1.6 ± 0.2) × 10-11 exp(340 ± 30 K/T) cm3 s-1 molecule-1 (2σ errors). In combination with the recent theoretically determined branching ratios for this reaction of this laboratory (Vereecken, L.; Sumathy, R.; Carl, S. A.; Peeters, J. Chem. Phys. Lett. 2001, 344, 400), the temperature dependencies of the two dominant product channels, HCN + CO2 and HCNO + CO, may be described by k5a = (3.7 ± 0.3) × 10-10T-0.72±0.02 exp(200 ± 30 K/T) cm3 s-1 molecule-1 and k5b = (1.4 ± 0.2) × 10-11 exp(320 ± 30 K/T) cm3 s-1 molecule-1, respectively, where the given (2σ) error limits are derived from those of the present experimental work only.