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Rate constant and RRKM product study for the reaction between CH 3 and C 2 H 3 at T = 298 K
Author(s) -
Thorn, R. Peyton,
Payne, Walter A.,
Chillier Xavier D. F.,
Stief Louis J.,
Nesbitt Fred L.,
Tardy D. C.
Publication year - 2000
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/(sici)1097-4601(2000)32:5<304::aid-kin6>3.0.co;2-j
Subject(s) - chemistry , disproportionation , reaction rate constant , analytical chemistry (journal) , torr , radical , decomposition , thermodynamics , kinetics , organic chemistry , physics , quantum mechanics , catalysis
The total rate constant k 1 has been determined at P = 1 Torr nominal pressure (He) and at T = 298 K for the vinyl‐methyl cross‐radical reaction: (1) CH 3 + C 2 H 3 → 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 C 2 H 4 and CH 4 , respectively. The kinetic studies were performed by monitoring the decay of C 2 H 3 with methyl in excess, 6 < [CH 3 ] 0 / [C 2 H 3 ] 0 < 21. The overall rate coefficient was determined to be k 1 (298 K) = (1.02 ± 0.53) × 10 −10 cm 3 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 C 2 H 3 + H and C 2 H 3 + C 2 H 3 . The present result for k 1 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 CH 3 + C 2 H 5 and with a value for k 1 estimated by the geometric mean rule employing values for k (CH 3 + CH 3 ) and k (C 2 H 3 + C 2 H 3 ). Qualitative product studies at T = 298 K and 200 K indicated formation of C 3 H 6 , C 2 H 2 , and C 3 H 5 as products of the combination‐stabilization, disproportionation, and combination‐decomposition channels, respectively, of the CH 3 + C 2 H 3 reaction. We also observed the secondary C 4 H 8 product of the subsequent reaction of C 3 H 5 with excess CH 3 ; this observation provides convincing evidence for the combination‐decomposition channel yielding C 3 H 5 + 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. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 304–316, 2000