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Author(s):   Zhu, R.S.; Xu, Z.F.; Lin, M.C.
Title:   Ab initio studies of alkyl radical reactions: Combination and disproportionation reactions of CH3 with C2H5, and the decomposition of chemically activated C3H8
Journal:   J. Chem. Phys.
Volume:   120
Page(s):   6566 - 6573
Year:   2004
Reference type:   Journal article
Squib:   2004ZHU/XU6566-6573

Reaction:   ·C2H5 + ·CH3CH4 + C2H4
Reaction order:   2
Temperature:   200 - 600 K
Rate expression:   5.21x101 [cm3/molecule s] (T/298 K)0.41 e3567 [J/mole]/RT
Category:  Theory
Data type:   Ab initio
Comments:   The CH3 + C2H5 reaction was investigated by the modified Gaussian-2 method with variational transition state or Rice-Ramsperger-Kassel-Marcus calculations. Vibrational frequencies and moments of inertia of all species used in RRKM calculations were computed at the B3LYP/6-3-11G(3df,2p) level and are reported.

The results suggest the combination process dominates below 600 K and is pressure independent under typical experimental conditions. The disproportionation process producing CH4 and C2H4 is suggested to occur via a loose hydrogen-bonded precursor, H3C---HC2H4 , which fragments with a small ~1.9 kcal/mol! barrier giving rise to the products. The disproportionation and combination reactions are concluded to occur with entirely different transition states. Calculated rate constants are in ggod agreement with experimental values.

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Rate constant values calculated from the Arrhenius expression:

T (K)k(T) [cm3/molecule s]
200 3.78E2
225 3.13E2
250 2.70E2
275 2.40E2
300 2.18E2
325 2.02E2
350 1.90E2
375 1.80E2
400 1.72E2
425 1.65E2
450 1.60E2
475 1.56E2
500 1.52E2
525 1.49E2
550 1.46E2
575 1.44E2
600 1.42E2