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

The recombination of c‐C5H5 with H‐atoms has been studied behind reflected shock waves. The obtained rate coefficients are almost independent of temperature and were found to be krec = 2.6 × 1014 cm3 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 Kc(T) for C5H6 ⇌ c‐C5H5 + H. A “third law” analysis was performed. Data for the enthalpy of formation of cyclopentadienyl DHf,0 = 65.4 ± 1 kcal mol−1 and DHf,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.