Experimental Investigation of the Reaction between Nitric Oxide and Ketenyl Radicals (HCCO + NO): Rate Coefficient at T = 290-670 K and Product Distribution at 700 K

Abstract

The HCCO + N O reaction (r5) was investigated in C2H2/0/NO systems at a pressure of 2 Torr (He bath gas) using discharge flow-molecular beam mass spectrometry techniques (DF-MBMS). The first rate coefficient data at temperatures > 300 K are presented. The coefficient was measured relative to the known k(HCCO+O) from the changeof steady-state HCCO signals upon adding increasing amounts of NO. Thus, in the temperature range from 290 to 670 K, the k(HCCO+NO) coefficient was found to exhibit a slight but significant temperature dependence: k(T) = (1.0 f 0.3) X 10-lo e-(350*150)/(TIQ cm3 molecule-' (T = 290-670 K). The product distribution was determined at 700 K. The experiments relied on the fact that all reaction pathways yield either CO or C02. Ketenyl radicals, generated by quantitative reaction of a known amount of 0 atoms with C2H2 in high excess, were reacted with a large excess of NO, ensuring quantitative conversion into the products C02 and CO. The product distribution was essentially deduced from the ratios [CO2]fomd/[O]input and [CO]for,d/ [O]inPut. Formation of CO together with CHz(3B1) in a minor (25 f 15%) channel of the C2H2 + 0 reaction was taken into account. Small corrections for secondary reactions such as HCCO + 0 -H + 2 CO were made by kinetic modeling. Thus, the following yields were obtained: for HCCO + N O -(CHNO) + CO, 77 f 9%; for HCCO + N O -(CHN) + C02, 23 f 9%. Strong product signals were also observed at m / e = 43 and m / e = 27, confirming that CHNO isomers and C H N isomers are formed along with CO and COz, respectively.Theoretical predictions regarding the CO/CO2 yield ratio, presented in a companion paper in this issue, can be reconciled with the experimental product distribution only when an as yet unidentified entrance pathway to the formyl isocyanate intermediate is assumed to exist and to be thermally accessible.

An investigation of important gas-phase reactions of nitrogenous species from the simulation of experimental measurements in combustion systems

“…There are two room temperature measurements of the overall rate coefficient of 1. , respectively. Boullart et al [50] measured the rate coefficient between 290 to 670 K, using the technique of discharge flow with molecular beam mass spectrometry, and observed a slight temperature dependence. At 700 K, they also measured the product branching ratio, obtaining 77% via the CO channel and 23% via the CO 2 channel.…”

Experimental and kinetic modeling of the reduction of NO by isobutane in a Jsr at 1 atm

“…Recently, Eickhoff and Temps [19] using FTIR spectroscopy measured a branching ratio at room temperature in agreement with [16] and were able to definitively demonstrate that fulminic acid, HCNO, was the product of reaction (93) and that isocyanic acid, HNCO, was not formed at detectable levels of concentration. The product distribution of the reaction HCCO ϩ NO at 550 and 700 K was reported recently by Van Poppel and Peeters [20].…”

“…According to earlier modeling efforts [4,12] the sequence of reactions HCCO ϩ NO : HCNO ϩ CO and HCN ϩ CO 2 , followed by HCNO ϩ H : HCN ϩ OH, mostly accounts for the observed reduction of NO. The kinetics of the reaction between ketenyl and NO have been studied both experimentally [16] and theoretically [17,18]. It was found [16,17] that at 700 K this reaction proceeds through two channels:…”

“…The kinetics of the reaction between ketenyl and NO have been studied both experimentally [16] and theoretically [17,18]. It was found [16,17] that at 700 K this reaction proceeds through two channels:…”

“…In their mass spectrometric study, Boullart et al [16] established that the channel-forming CO dominates at 700 K. However, they could not identify the product (HCNO) by mass spectrometry. Recently, Eickhoff and Temps [19] using FTIR spectroscopy measured a branching ratio at room temperature in agreement with [16] and were able to definitively demonstrate that fulminic acid, HCNO, was the product of reaction (93) and that isocyanic acid, HNCO, was not formed at detectable levels of concentration.…”