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 tempe rature and were found to be k(rec) = 2.6 x 10(14) cm(3) mol(-1) s(-1) for p ressures around 2 bar in the temperature range between 1150 and 1500 K. Tog ether with rate coefficients for th e dissociation, obtained in an earlier work (Roy et al., Proc Combust Inst 1998, 27, 329-336) at pressures and tem peratures close to those applied in the present work, we calculated equilib rium constants K-C(T) for C5H6 reversible arrow c-C5H5 + H. A "third law" a nalysis was performed. Data for the enthalpy of formation of cyclopentadien yl DHf,0 = 65.4 +/- 1 kcal mol(-1) and DHf,298 = 62.5 +/- 1 kcal mol(-1) we re derived, respectively. The analysis was based upon new results on the en tropy of cyclopentadienyl, recently calculated by Kiefer et al. (J phy chem , in press). Finally, our measured data were subjected to a fall-off analys is. The simulation turned out very satisfactorily. (C) 2001 John Wiley & So ns, Inc.