Reanalysis of Rate Data for the Reaction CH3 + CH3 → C2H6 Using Revised Cross Sections and a Linearized Second-Order Master Equation

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, 9, 2455-2462). These corrections necessitated the development of a detailed model of the (B) over tilde (2)A(1)' (3s) - (X) over tilde (2)A(2)'' 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(infinity)(T); it was Used to fit the experimental rate coefficients using the Levenberg- Marquardt algorithm to minimize chi(2) calculated from the differences between experimental and calculated rate coefficients. Parameters for both k(infinity)(T) and for energy transfer (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(infinity)(T) = 5.76 X 10(-11)(T/298 K)-(0.34) cm(3) molecule(-1) s(-1) was obtained, which agrees well with the best available theoretical expression.