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Rate Constant and RRKM Product Study for the Reaction Between CH3 and C2H3 at T = 298KThe 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 CH3 + C2H3 yields 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|(sub 0)/|C2H3|(sub 0) < 21. The overall rate coefficient was determined to be k1(298 K) = (1.02 +/- 0.53)x10(exp -10) cubic cm/molecule/s 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 C2H5 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.
Document ID
Document Type
Reprint (Version printed in journal)
Thorn, R. Peyton, Jr. (NASA Goddard Space Flight Center Greenbelt, MD United States)
Payne, Walter A., Jr. (NASA Goddard Space Flight Center Greenbelt, MD United States)
Chillier, Xavier D. F. (NASA Goddard Space Flight Center Greenbelt, MD United States)
Stief, Louis J. (NASA Goddard Space Flight Center Greenbelt, MD United States)
Nesbitt, Fred L. (Coppin State Coll. Baltimore, MD United States)
Tardy, D. C. (Iowa Univ. Iowa City, IA United States)
Date Acquired
August 20, 2013
Publication Date
January 1, 2000
Publication Information
Publication: International Journal of Chemical Kinetics
Volume: 32
Subject Category
Inorganic, Organic and Physical Chemistry
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