Kinetics and products of propargyl (C3H3) radical self-reactions and propargyl-methyl cross-combination reactions

Abstract

Propargyl (HC#C 9 CH 2 ) and methyl radicals were produced through the 193-nm excimer laser photolysis of mixtures of C 3 H 3 Cl/He and CH 3 N 2 CH 3 /He, respectively. Gas chromatographic and mass spectrometric (GC/MS) product analyses were employed to characterize and quantify the major reaction products. The rate constants for propargyl radical self-reactions and propargyl-methyl cross-combination reactions were determined through kinetic modeling and comparative rate determination methods. The major products of the propargyl radical combination reaction, at room temperature and total pressure of about 6.7 kPa (50 Torr) consisted of three C 6 H 6 isomers with 1,5-hexadiyne(CH # C 9CH 2 9CH 2 9C #CH, about 60%); 1,2-hexadiene-5yne (CH 2 " C "C9CH 2 9C#CH, about 25%); and a third isomer of C 6 H 6 (ϳ15%), which has not yet been, with certainty, identified as being the major products. The rate constant determination in the propargyl-methyl mixed radical system yielded a value of (4.0 Ϯ 0.4) ϫ 10 Ϫ11 cm 3 molecule Ϫ1 s Ϫ1 for propargyl radical combination reactions and a rate constant of (1.5 Ϯ 0.3) ϫ 10 Ϫ10 cm 3 molecule Ϫ1 s Ϫ1 for propargyl-methyl cross-combination reactions. The products of the methyl-propargyl cross-combination reactions were two isomers of C 4 H 6 , 1-butyne (about 60%) and 1,2-butadiene (about 40%).

Propargyl recombination: estimation of the high temperature, low pressure rate constant from flame measurements

“…The agreement between theory and measurements is generally very good, but the validation is mostly limited to lower temperatures. Most of the experimental results for the C 3 H 3 + C 3 H 3 rate constant are obtained below 700 K [20][21][22][23][24][25]; only a few studies extend to higher temperatures [26,27].…”

“…The agreement between our value and the Miller and Klippenstein estimate for the C 6 H 5 + H channel should not be attributed too much importance, as the product distribution in the reaction is uncertain. The results of the present work are also in good agree- Open symbols denote low pressure data [20][21][22][23][24]26], while closed symbols denote results obtained at atmospheric pressure or higher [25,27]. The solid and dashed lines denote the theoretical values for the total reaction and the phenyl + H channel, respectively, at 30 Torr [19].…”

On the Composition of Young, Directly Imaged Giant Planets

“…Because of a lack of laboratory or theoretical kinetic information on reactions of C 3 H 2 and C 3 H 3 with other hydrocarbon radicals under relevant low-pressure, reducing conditions, the fate of these C 3 H x species is not obvious (see also Moses et al 2011;Hébrard et al 2013). Three-body addition reactions of C 3 H 2 and C 3 H 3 with abundant ambient H atoms can lead to C 3 H 3 and C 3 H 4 , respectively, and the C 3 H 3 can react with CH 3 to form C 4 H 6 (Fahr & Nayak 2000;Knyazev & Slagle 2001) or self-react to form various C 6 H 6 isomers (Atkinson & Hudgens 1999;Fahr & Nayak 2000), but these three-body reactions are not particularly effective at low pressures. Therefore, C 3 H 2 and C 3 H 3 build up to mixing ratios of a few×10 −8 at high altitudes in our 10 au young-Jupiter model.…”

“…Benzene (C 6 H 6 ) itself is produced in our models through C 3 H 3 -C 3 H 3 recombination, which first goes through a linear C 6 H 6 isomer before eventual production of benzene (Fahr & Nayak 2000). The benzene mixing ratio reaches 1 ppb in our 10 au model (see Figure 7), but neither benzene nor any of the other relatively light hydrocarbons considered by our model become abundant enough to achieve saturation and condense.…”

Determination of the rate coefficient for the C3H3+ C3H3 reaction at high temperatures by shock-tube investigations

“…The authors used a laser photolysis/photoionization mass spectrometry setup and obtained rate coefficients decreasing from 3.3 · 10 À11 cm 3 s À1 at 500 K to 1.2 · 10 À11 cm 3 s À1 at 1000 K. Note that the latter value is in agreement with the result from Scherer et al [11] though the pressures in these two studies differ by more than two orders of magnitude. Besides four experimental studies at room temperature [9,[13][14][15], there are two more investigations at elevated temperatures but significantly below 1000 K [16,17]. For the sake of brevity, we present the rate coefficients from all these works summarized in Table 1.…”