Departments of Chemistry and Physics, University of California , Berkeley, California 94720, United States.
J Phys Chem A. 2013 Jun 20;117(24):5093-105. doi: 10.1021/jp403637t. Epub 2013 Jun 11.
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.
C2H 自由基与 C4H8 异构体 1-丁烯、顺式-2-丁烯、反式-2-丁烯和异丁烯的反应在 79 K 下通过激光光解-真空紫外质谱在拉瓦尔喷嘴膨胀中进行研究。通过在准一级条件下测量反应产物形成速率作为反应物密度的函数，获得双分子反应速率常数。速率常数分别为（1.9 ± 0.5）×10(-10)、（1.7 ± 0.5）×10(-10)、（2.1 ± 0.7）×10(-10)和（1.8 ± 0.9）×10(-10)cm(3)s(-1)，用于 C2H 与 1-丁烯、顺式-2-丁烯、反式-2-丁烯和异丁烯的反应。1-丁烯和异丁烯的双分子速率常数与先前在 103 K 下使用 C2H 化学发光测量的值很好地吻合。测量了反应产物的光电子能谱并拟合为贡献异构体的光电子能谱。结合绝对光电子截面，这些拟合提供了异构体分辨的产物分支分数。C2H 与 1-丁烯的反应以乙烯基乙炔的形式生成（65 ± 10）%的 C4H4 和以 4-戊烯-1-炔的形式生成（35 ± 10）%的 C5H6。顺式-2-丁烯和反式-2-丁烯的反应仅生成 3-戊烯-1-炔，并且无法区分顺式和反式 3-戊烯-1-炔。最后，异丁烯的反应生成（26 ± 15）%的 3-戊烯-1-炔、（35 ± 15）%的 2-甲基-1-丁烯-3-炔和（39 ± 15）%的 4-甲基-3-戊烯-1-炔。报告的 C2H 和丁烯反应的分支分数表明，这些反应优先通过 CH3 或 C2H3 消除而不是 H 原子消除进行。在实验不确定度范围内，没有发现形成环状物质的证据。
