Wide temperature range (T = 295 K and 770–1305 K) study of the kinetics of the reactions HCO + NO and HCO + NO2 using frequency modulation spectroscopy

Abstract

The rate constants for , HCO + NO --> HNO + CO, and , HCO + NO(2)--> products, have been measured at temperatures between 770 K < T < 1305 K behind reflected shock waves and, for the purpose of a consistency check, in a slow flow reactor at room temperature. HCO radicals were generated by 193 nm excimer laser photolysis of diluted gas mixtures containing glyoxal, (CHO)(2), and NO or NO(2) in argon and were monitored using frequency modulation (FM) absorption spectroscopy. Kinetic simulations based on a comprehensive reaction mechanism showed that the rate constants for the title reactions could be sensitively extracted from the measured HCO profiles. The determined high temperature rate constants are k(1)(769-1307 K) = (7.1 +/- 2.7) x 10(12) cm(3) mol(-1) s(-1) and k(2)(804-1186 K) = (3.3 +/- 1.8) x 10(13) cm(3) mol(-1) s(-1). The room temperature values were found to be in very good agreement with existing literature data and show that both reactions are essentially temperature independent. The weak temperature dependence of can be explained by the interplay of a dominating direct abstraction pathway and a complex-forming mechanism. Both pathways yield the products HNO + CO. In contrast to , no evidence for a significant contribution of a direct high temperature abstraction channel was found for . Here, the observed temperature independent overall rate constant can be described by a complex-forming mechanism with several product channels. Detailed information on the strongly temperature dependent channel branching ratios is provided. Moreover, the high temperature rate constant of , OH + (CHO)(2), has been determined to be k(7) approximately 1.1 x 10(13) cm(3) mol(-1) s(-1).

Nitromethane ignition behind reflected shock waves: Experimental and numerical study

“…The reaction coefficient used for this reaction is around two times faster for the model of the present study (reaction coming from the mechanism of Kéromnès et al [53]) than for the other models (both using the same rate, from Desain et al [ , whereas this reaction is not among the 10 most-sensitive reactions for the model of the present study. For the model of the present study and for the model of Brequigny et al, the most important inhibiting reaction is R3 ( = -0.76 and -0.78, respectively, both models using the same rate from Xu et al [46]), and this reaction is also important for the model of Zhang et al ( = -0.47, using the rate from Dammeier et al [55]). Note that R3 also has a noticeable importance for the model of the present study and the model of Brequigny et al at 895 K, whereas R6 was not in the 10 most-sensitive reactions for the model of Zhang and coworkers at low temperature.…”

The rate constant of the reaction NCN + H2 and its role in NCN and NO modeling in low pressure CH4/O2/N2-flames

“…It is known that H abstraction channels often become the dominating pathway at high temperatures even if complex-forming pathways are accessible. 26,37 Therefore, the most reasonable reaction products HNCN + H have been assumed for the target reaction NCN + H 2 in the first round of data evaluation. The effect of assuming different product sets will be further discussed below.…”

Sensitizing effects of NOx on CH4 oxidation at high pressure

“…The competing association/stabilization channel to HC(O)NO is strongly pressure-dependent, but it also has a strong negative temperature dependence that makes it insignificant except under highpressure/low-temperature conditions (>10 bar and <298 K) [127]. Dammeier et al [126] measured the overall rate constant of NO 2 + HCO (k 13 +k 14 +k 15 ) and reviewed existing experimental data to estimate the individual branching ratios used in the mechanism. The value of k 13 +k 14 +k 15 exceeds the recommendation from Tsang and Herron [129] by 25-60% at temperatures between 298 and 1400 K, but this is within the uncertainty limits of the rate constant from Tsang and Herron.…”

“…Formyl radicals (HCO) are converted rapidly and without energy barrier to CO or CO 2 in the presence of NO x (R2, R13-R15). The rate constants are drawn from a recent shock tube study by Dammeier et al [126], who measured the title reactions at nearatmospheric pressure and intermediate to high temperatures (770-1305 K and 805-1190 K for NO + HCO and NO 2 + HCO, respectively). The value of k 2 ranges within 21% of the recent ab initio calculations by Xu et al [127] at 500-1500 K and the flash-photolysis experiments of Veyret and Lesclaux [128] at 298-503 K. The present mechanism only includes the H-abstraction channel from NO + HCO (R2).…”