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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:   600 - 3000 K
Rate expression:   2.26x10-14 [cm3/molecule s] (T/298 K)2.45 e12222 [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/6-311G(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]
600 1.45E-12
700 1.50E-12
800 1.60E-12
900 1.74E-12
1000 1.91E-12
1100 2.11E-12
1200 2.33E-12
1300 2.59E-12
1400 2.86E-12
1500 3.16E-12
1600 3.48E-12
1700 3.82E-12
1800 4.19E-12
1900 4.58E-12
2000 5.00E-12
2100 5.44E-12
2200 5.91E-12
2300 6.40E-12
2400 6.91E-12
2500 7.46E-12
2600 8.03E-12
2700 8.62E-12
2800 9.24E-12
2900 9.89E-12
3000 1.06E-11