Kinetics of the cyclopentadiene decay and the recombination of cyclopentadienyl radicals with H‐atoms: Enthalpy of formation of the cyclopentadienyl radical

Abstract

The recombination of c-C 5 H 5 with H-atoms has been studied behind reflected shock waves. The obtained rate coefficients are almost independent of temperature and were found to be k rec = 2.6 × 10 14 cm 3 mol −1 s −1 for pressures around 2 bar in the temperature range between 1150 and 1500 K. Together with rate coefficients for the dissociation, obtained in an earlier work (Roy et al., Proc Combust Inst 1998, 27, 329-336) at pressures and temperatures close to those applied in the present work, we calculated equilibrium constants K c (T) for C 5 H 6 c-C 5 H 5 + H. A "third law" analysis was performed. Data for the enthalpy of formation of cyclopentadienyl DH f,0 = 65.4 ± 1 kcal mol −1 and DH f,298 = 62.5 ± 1 kcal mol −1 were derived, respectively. The analysis was based upon new results on the entropy of cyclopentadienyl, recently calculated by Kiefer et al. (J phy chem, in press). Finally, our measured data were subjected to a fall-off analysis. The simulation turned out very satisfactorily.

Thermochemical properties from G3MP2B3 calculations, Set‐2: Free radicals with special consideration of CH2CHC•CH2, cyclo−•C5H5, •CH2OOH, HO•CO, and HC(O)O•

“…The effect of vibronic coupling and pseudorotation on the entropy is noticeable. Owing to the rapid pseudorotation that is faster than free rotation, the entropy is lower in the JT treatment, S o (298.15) = 265.7 J mol −1 K −1 [44,45], than in the RR-HO approach (Table II) [3,5,43,45,46]. Different computational methods are less consistent in the prediction of the JT stabilization energy ε T ( 2 E 1 − 2 A 2 ).…”

“…• CO has been observed using matrix iso- lation spectroscopy at low temperature [67], and some of its reactions have been measured in the gas phase [68] whereas HC(O)O • , isomeric to HO • CO, does not seem to be associated with a stable, hence observable free radical species in view of its proximity to the lowlying transition structure TS 5 . Previous ab initio calculations of the potential energy surface of reaction (4) have emphasized the stationary points along the reaction coordinate [69,70].…”

Experimental and modeling study of the oxidation of benzene

“…The reactions with oxygen atoms and molecules are those proposed by Zhong and Bozzelli 39 in their theoretical study of the reactions of cyclopentadienyl radicals. The reactions of cyclopentadienyl radicals have also been studied by Roy et al 42, 57. The C 10 H 10 compound obtained by combination of two cyclopentadienyl radicals (61) is dihydrofulvalene.…”

“…The rate constants of most reactions of cyclopentadienyl radicals are based on calculations or estimations. The very few direct measurements of rate constants for these radicals have been obtained at high temperature in a shock tube 33, 57.…”

Experimental and modeling studies of C2H4/O2/Ar, C2H4/methylal/O2/Ar and C2H4/ethylal/O2/Ar rich flames and the effect of oxygenated additives

“…By decomposition of the phenoxy radical, cyclopentadienyl radical (C 5 H 5 ) and carbon monoxide are produced (CO), C 6 H 5 O = CO + C 5 H 5 (R.9), with k 9 = 7.4 Â 10 11 exp(À22,182/T) [s À1 ] from Frank et al [52]. The model indicates that cyclopentadiene (C 5 H 6 ) is mainly formed by the reverse of the reaction R.10, C 5 H 6 = C 5 H 5 + H with k 10 = 7.65 Â 10 19 T À1.18 exp(À42,663/T) [s À1 ] from Roy et al [53]. Therefore, the concentration of C 5 H 6 depends on benzene concentration through this mechanism.…”