Unimolecular isomerization/decomposition of cyclopentadienyl and related bimolecular reverse process:ab initio MO/statistical theory study

Abstract

The cyclopentadienyl radical decomposition has been studied in detail by high-level correlation MO methods combined with multichannel RRKM rate constant calculations. The product channels of the reaction were examined by calculating their pressure-dependent branching rate constants. The overall reaction rate has been shown to be controlled by the first transition state corresponding to 1,2-hydrogen atom migration. Also, the reverse bimolecular reactions (C 3 H 3 + C 2 H 2 → products) have been included in the study. We provide a summary of pressure dependent rate constant expressions for the 1000-3000 K temperature range that may be useful for kinetic modeling of relevant combustion systems.

Erratum: “Kinetics of the cyclopentadiene decay and the recombination of cyclopentadienyl radicals with H‐atoms: Enthalpy of formation of the cyclopentadienyl radical”, Int J Chem Kinet 2001, 33, 821

“…The latter value is somewhat smaller than a recent number DH f,298 = 65.3 ± 2 kcal mol −1 obtained by Kern et al [11], based upon their RRKM modeling of the cyclopentadiene decay measured at low pressures ranging from 100 to 450 Torr. However, our result compares favorably with recently theoretically obtained numbers by Wang and Brezinsky [12] and by Moskaleva and Lin [13] as well as with older experimental data from Bartmess et al [29] and DeFrees et al [29]. The determination of the enthalpy of formation of cyclopentadienyl was made possible only by taking the quite recently calculated entropy data for cyclopentadienyl from Kiefer et al [14].…”

“…This conclusion agrees with earlier calculations by Günthard and his coworkers [25b]. In both the recent investigations [12,13], it was proposed to model the valence isomerization by assuming a pseudo free rotor. Both groups ascribed a moment of inertia to this "pseudo free rotor" being equal to that belonging to the axis perpendicular to the molecular plane.…”

“…gov/chemistry)). Therefore, in case of the cyclopentadienyl radical we rely upon theoretical calculations performed, e.g., by Wang and Brezinsky [12], by Moskaleva and Lin [13], and quite recently by Kiefer et al [14]. The set of molecular parameters used in our calculations is given in Table III.…”

“…This is caused by the Jahn-Teller effect [26]. Recent quantum chemical calculations by Wang and Brezinsky [12] as well as by Moskaleva and Lin [13] have revealed that for this valence isomerization the pertinent barrier is almost negligible. This conclusion agrees with earlier calculations by Günthard and his coworkers [25b].…”

“…Presently, there exist larger uncertainties inherent in the published thermodynamic data. This refers to the enthalpy of formation as well as to the entropy of c-C 5 H 5 [11][12][13]. From our two sets of rate coefficients, obtained almost in the same temperature and pressure range, we calculated the equilibrium constants and derived from these the reaction enthalpy.…”