Department of Chemistry, University of California, Berkeley, California 94720, USA.
J Phys Chem A. 2010 Mar 11;114(9):3340-54. doi: 10.1021/jp911132r.
The rate coefficient for the reaction of the ethynyl radical (C(2)H) with 1-butyne (H-C[triple bond]C-CH(2)-CH(3)) is measured in a pulsed Laval nozzle apparatus. Ethynyl radicals are formed by laser photolysis of acetylene (C(2)H(2)) at 193 nm and detected via chemiluminescence (C(2)H + O(2) --> CH (A(2)Delta) + CO(2)). The rate coefficients are measured over the temperature range of 74-295 K. The C(2)H + 1-butyne reaction exhibits no barrier and occurs with rate constants close to the collision limit. The temperature-dependent rate coefficients can be fit within experimental uncertainties by the expression k = (2.4 +/- 0.5) x 10(-10)(T/295 K)(-(0.04+/-0.03)) cm(3) molecule(-1) s(-1). Reaction products are detected at room temperature (295 K) and 533 Pa using a multiplexed photoionization mass spectrometer (MPIMS) coupled to the tunable vacuum ultraviolet synchrotron radiation from the Advanced Light Source at the Lawrence Berkeley National Laboratory. Two product channels are identified for this reaction: m/z = 64 (C(5)H(4)) and m/z = 78 (C(6)H(6)) corresponding to the CH(3)-loss and H-loss channels, respectively. Photoionization efficiency (PIE) curves are used to analyze the isomeric composition of both product channels. The C(5)H(4) products are found to be exclusively linear isomers composed of ethynylallene and methyldiacetylene in a 4:1 ratio. In contrast, the C(6)H(6) product channel includes two cyclic isomers, fulvene 18(+/-5)% and 3,4-dimethylenecyclobut-1-ene (DMCB) 32(+/-8)%, as well as three linear isomers, 2-ethynyl-1,3-butadiene 8(+/-5)%, 3,4-hexadiene-1-yne 28(+/-8)%, and 1,3-hexadiyne 14(+/-5)%. Within experimental uncertainties, we do not see appreciable amounts of benzene and an upper limit of 10% is estimated. Diacetylene (C(4)H(2)) formation via the C(2)H(5)-loss channel is also thermodynamically possible but cannot be observed due to experimental limitations. The implications of these results for modeling of planetary atmospheres, especially of Saturn's largest moon Titan and the relationships to combustion reactions, are discussed.
用脉冲式激波管装置测量了乙炔基（C(2)H）与 1-丁炔（H-C[三键]C-CH(2)-CH(3)）反应的速率系数。乙炔基自由基通过 193nm 激光光解乙炔（C(2)H(2)）形成，并通过化学发光（C(2)H + O(2) --> CH (A(2)Delta) + CO(2)）检测。在 74-295 K 的温度范围内测量了速率系数。C(2)H + 1-丁炔反应没有势垒，并且以接近碰撞极限的速率常数发生。在实验不确定度范围内，可以通过表达式 k = (2.4 +/- 0.5) x 10(-10)(T/295 K)-(0.04+/-0.03)) cm(3) molecule(-1) s(-1) 拟合温度相关的速率系数。在室温（295 K）和 533 Pa 下，使用多路复用光电离质谱仪（MPIMS）与劳伦斯伯克利国家实验室可调谐真空紫外同步辐射相结合，检测到反应产物。该反应鉴定出两个产物通道：m/z = 64（C(5)H(4)）和 m/z = 78（C(6)H(6)），分别对应于 CH(3)-损失和 H-损失通道。使用光电离效率（PIE）曲线分析两个产物通道的异构体组成。发现 C(5)H(4)产物仅为炔丙基丙二烯和甲基丙二炔的线性异构体，比例为 4:1。相比之下，C(6)H(6)产物通道包括两种环状异构体，富烯 18(+/-5)%和 3,4-二亚甲基环丁-1-烯（DMCB）32(+/-8)%，以及三种线性异构体，2-乙炔基-1,3-丁二烯 8(+/-5)%、3,4-己二烯-1-炔 28(+/-8)%和 1,3-己二炔 14(+/-5)%。在实验不确定度范围内，我们没有看到可观数量的苯，估计上限为 10%。通过 C(2)H(5)-损失通道形成二乙炔（C(4)H(2)）在热力学上也是可能的，但由于实验限制无法观察到。这些结果对行星大气的建模，特别是对土星最大的卫星泰坦以及与燃烧反应的关系的影响进行了讨论。
