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Rate constant and RRKM product study for the reaction between CH3 and C2H3 at T = 298 K

Thorn, R. Peyton
Payne, Walter A.
Stief, Louis J.
Nesbitt, Fred L.
Tardy, D. C.
Published in International Journal of Chemical Kinetics. 2000, vol. 32, no. 5, p. 304-316
Abstract The total rate constant k1 has been determined at P = 1 Torr nominal pressure (He) and at T = 298 K for the vinyl-methyl cross-radical reaction: (1) CH3 + C2H3 Products. The measurements were performed in a discharge flow system coupled with collision-free sampling to a mass spectrometer operated at low electron energies. Vinyl and methyl radicals were generated by the reactions of F with C2H4 and CH4, respectively. The kinetic studies were performed by monitoring the decay of C2H3 with methyl in excess, 6 < [CH3]0/ [C2H3]0 < 21. The overall rate coefficient was determined to be k1(298 K) = (1.02 ± 0.53) × 10-10 cm3 molecule-1 s-1 with the quoted uncertainty representing total errors. Numerical modeling was required to correct for secondary vinyl consumption by reactions such as C2H3 + H and C2H3 + C2H3. The present result for k1 at T = 298 K is compared to two previous studies at high pressure (100-300 Torr He) and to a very recent study at low pressure (0.9-3.7 Torr He). Comparison is also made with the rate constant for the similar reaction CH3 + C2H5 and with a value for k1 estimated by the geometric mean rule employing values for k(CH3 + CH3) and k(C2H3 + C2H3). Qualitative product studies at T = 298 K and 200 K indicated formation of C3H6, C2H2, and C3H5 as products of the combination-stabilization, disproportionation, and combination-decomposition channels, respectively, of the CH3 + C2H3 reaction. We also observed the secondary C4H8 product of the subsequent reaction of C3H5 with excess CH3; this observation provides convincing evidence for the combination-decomposition channel yielding C3H5 + H. RRKM calculations with helium as the deactivator support the present and very recent experimental observations that allylic C-H bond rupture is an important path in the combination reaction. The pressure and temperature dependencies of the branching fractions are also predicted.
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Research group Groupe Weber
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THORN, R. Peyton et al. Rate constant and RRKM product study for the reaction between CH3 and C2H3 at T = 298 K. In: International Journal of Chemical Kinetics, 2000, vol. 32, n° 5, p. 304-316. https://archive-ouverte.unige.ch/unige:3720

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Deposited on : 2009-10-06

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