Journal of Physical Chemistry A vol:106 issue:51 pages:12242-12247
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(X(2)Pi) photofragment. The rate coefficient of the title reaction was found to exhibit a negative temperature dependence described by k(5)(T)((HCCO+NO)) (1.6 +/- 0.2) x 10(-11) exp(340 +/- 30 K/T) cm(3) s(-1) molecule(-1) (2sigma 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 k(5a) = (3.7 +/- 0.3) x 10(-10)T-(0.72) (+/- 0.02) exp(200 +/- 30 K/T) cm(3) s(-1) molecule(-1) and k(5b) = (1.4 +/- 0.2) x 10(-11) exp(320 +/- 30 K/T) cm(3) s(-1) molecule(1), respectively, where the given (2sigma) error limits are derived from those of the present experimental work only.