Reaction Rate and Isomer-Specific Product Branching Ratios of C2H + C4H8: 1-Butene, cis-2-Butene, trans-2-Butene, and Isobutene at 79 K. - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Journal of Physical Chemistry A Année : 2013

Reaction Rate and Isomer-Specific Product Branching Ratios of C2H + C4H8: 1-Butene, cis-2-Butene, trans-2-Butene, and Isobutene at 79 K.

Résumé

The reactions of C2H radicals with C4H8 isomers 1-butene, cis-2-butene, trans-2-butene, and isobutene are studied by laser photolysis-vacuum ultraviolet mass spectrometry in a Laval nozzle expansion at 79 K. Bimolecular-reaction rate constants are obtained by measuring the formation rate of the reaction product species as a function of the reactant density under pseudo-first-order conditions. The rate constants are (1.9 ± 0.5) × 10(-10), (1.7 ± 0.5) × 10(-10), (2.1 ± 0.7) × 10(-10), and (1.8 ± 0.9) × 10(-10) cm(3) s(-1) for the reaction of C2H with 1-butene, cis-2-butene, trans-2-butene, and isobutene, respectively. Bimolecular rate constants for 1-butene and isobutene compare well to values measured previously at 103 K using C2H chemiluminescence. Photoionization spectra of the reaction products are measured and fitted to ionization spectra of the contributing isomers. In conjunction with absolute-ionization cross sections, these fits provide isomer-resolved product branching fractions. The reaction between C2H and 1-butene yields (65 ± 10)% C4H4 in the form of vinylacetylene and (35 ± 10)% C5H6 in the form of 4-penten-1-yne. The cis-2-butene and trans-2-butene reactions yield solely 3-penten-1-yne, and no discrimination is made between cis- and trans-3-penten-1-yne. Last, the isobutene reaction yields (26 ± 15)% 3-penten-1-yne, (35 ± 15)% 2-methyl-1-buten-3-yne, and (39 ± 15)% 4-methyl-3-penten-1-yne. The branching fractions reported for the C2H and butene reactions indicate that these reactions preferentially proceed via CH3 or C2H3 elimination rather than H-atom elimination. Within the experimental uncertainties, no evidence is found for the formation of cyclic species.
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Dates et versions

hal-00844546 , version 1 (15-07-2013)

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Jordy Bouwman, Martin Fournier, Ian R Sims, Stephen R. Leone, Kevin R. Wilson. Reaction Rate and Isomer-Specific Product Branching Ratios of C2H + C4H8: 1-Butene, cis-2-Butene, trans-2-Butene, and Isobutene at 79 K.. Journal of Physical Chemistry A, 2013, 117 (24), pp.5093-5105. ⟨10.1021/jp403637t⟩. ⟨hal-00844546⟩
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