title: Reanalysis of Rate Data for the Reaction CH3 + CH3 → C2H6 Using Revised Cross Sections and a Linearized Second-Order Master Equation.
abstract: Rate coefficients for the CH3 + CH3 reaction, over the temperature range 300-900 K, have been corrected for errors in the absorption coefficients used in the original publication ( Slagle et al., J. Phys. Chem. 1988 , 92 , 2455 - 2462 ). These corrections necessitated the development of a detailed model of the B̃(2)A1' (3s)-X̃(2)A2″ transition in CH3 and its validation against both low temperature and high temperature experimental absorption cross sections. A master equation (ME) model was developed, using a local linearization of the second-order decay, which allows the use of standard matrix diagonalization methods for the determination of the rate coefficients for CH3 + CH3. The ME model utilized inverse Laplace transformation to link the microcanonical rate constants for dissociation of C2H6 to the limiting high pressure rate coefficient for association, k∞(T); it was used to fit the experimental rate coefficients using the Levenberg-Marquardt algorithm to minimize χ(2) calculated from the differences between experimental and calculated rate coefficients. Parameters for both k∞(T) and for energy transfer ⟨ΔE⟩down(T) were varied and optimized in the fitting procedure. A wide range of experimental data were fitted, covering the temperature range 300-2000 K. A high pressure limit of k∞(T) = 5.76 × 10(-11)(T/298 K)(-0.34) cm(3) molecule(-1) s(-1) was obtained, which agrees well with the best available theoretical expression.
authors.affiliation: †School of Chemistry, University of Leeds, Leeds LS2 9JT, U.K.
authors.forename: M A
authors.initials: MA
authors.lastname: Blitz
authors.affiliation: ‡Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, U.K.
authors.forename: N J B
authors.initials: NJ
authors.lastname: Green
authors.affiliation: †School of Chemistry, University of Leeds, Leeds LS2 9JT, U.K.
authors.forename: R J
authors.initials: RJ
authors.lastname: Shannon
authors.affiliation: †School of Chemistry, University of Leeds, Leeds LS2 9JT, U.K.
authors.forename: M J
authors.initials: MJ
authors.lastname: Pilling
authors.affiliation: †School of Chemistry, University of Leeds, Leeds LS2 9JT, U.K.
authors.forename: P W
authors.initials: PW
authors.lastname: Seakins
authors.affiliation: §School of Chemistry, Cantock's Close, Bristol BS8 1TS, U.K.
authors.forename: C M
authors.initials: CM
authors.lastname: Western
authors.affiliation: ∥Dassault Systèmes, BIOVIA, Science Park, Cambridge CB4 0WN, U.K.
authors.forename: S H
authors.initials: SH
authors.lastname: Robertson