Abstract
Thermal decomposition of cyclopentadiene to cβC~5~H~5~ (cyclopentadienyl radical) + H (1) and the reverse bimolecular reaction (β1) are studied quantumβchemically at the G2M level of theory. The dissociation pathway has been mapped out following the minimum energy path on the potential energy surface (PES) calculated by the density functional UB3LYP/6β311G(d,p) method. Using isodesmic reaction analysis, the standard enthalpy of formation for cβC~5~H~5~ is found to be 62.5 Β± 1.3 kcal mol^β1^, and the cβC~5~H~5~ο£ΏH bond dissociation energy is estimated as DΒ°~298~(cβC~5~H~5~ο£ΏH) = 82.5 Β± 0.9 kcal mol^β1^, in excellent agreement with the recent experimental values. Variational rate constants are computed on the basis of a scaled UB3LYP dissociation potential that fits the isodesmic/experimental enthalpy of Reaction (1). At the high pressure limit, k~1~^β^ = 1.55 Γ 10^18^ T^β0.8^ exp(β42300/T) s^β1^ and k~β1~^β^ = 2.67 Γ 10^14^ exp(β245/T) cm^3^ mol^β1^ s^β1^. The fallβoff effects are evaluated by a weak collision master equation/RRKM analysis. Calculated T, Pβdependent rate constants are in very good agreement with the most reliable experimental measurements. Β© 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 139β151 2004