Lu I-Chung, Chen Wei-Kan, Huang Wen-Jian, Lee Shih-Huang
Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan.
J Chem Phys. 2008 Oct 28;129(16):164304. doi: 10.1063/1.3000005.
We conducted the reaction C((3)P)+SiH(4) at a collision energy of 4.0 kcal mol(-1) in a crossed molecular-beam apparatus measuring time-of-flight mass spectra and selective photoionization. Product ions with m/z=41-43 are associated with two product channels, H(2)SiCH/HSiCH(2)/SiCH(3)+H and H(2)SiC/HSiCH/SiCH(2)+H(2). Apart from daughter ions and isotopic variants of reaction products, the species observed at m/z=43 is assigned to product H(2)SiCH/HSiCH(2)/SiCH(3) and that at m/z=42 to product H(2)SiC/HSiCH/SiCH(2). The signals observed at m/z=41 are due to dissociative ionization of silicon-carbon hydrides of these two types. We report time-of-flight spectra of products at specific laboratory angles and theoretical simulations, from which both kinetic-energy and angular distributions of products in the center-of-mass frame were derived. The release of kinetic energy is weakly dependent on the scattering angle for these two reactions. The channels for loss of H and H(2) release average translational energies of 10.5 and 16.7 kcal mol(-1), respectively. As hydrogen transfer before decomposition is facile, products H(2)SiCH/HSiCH(2)/SiCH(3) and H(2)SiC/HSiCH/SiCH(2) exhibit mildly forward/backward preferred and isotropic angular distributions, respectively. We estimate the branching ratios of these channels for loss of H and H(2) to be roughly 6:4. The measurements of release of kinetic energy and ionization thresholds of products indicate that SiCH(3)((2)A(")) and SiCH(2)((3)A(2)) are dominant among isomeric products. To explore the reaction mechanism, we computed the potential-energy surfaces for the reaction C((3)P)+SiH(4). The most likely mechanism is that atom C (3)P inserts into bond Si-H of SiH(4) in the entrance channel, and the reaction complex H(3)SiCH subsequently isomerizes to HSiCH(3) followed by decomposition to SiCH(3)((2)A("))+H and SiCH(2)((3)A(2))+H(2). We observed no significant evidence for the reaction C((1)D)+SiH(4).
我们在交叉分子束装置中，以4.0千卡·摩尔⁻¹的碰撞能量进行反应C((³P)) + SiH₄，该装置用于测量飞行时间质谱和选择性光电离。质荷比为m/z = 41 - 43的产物离子与两个产物通道相关，即H₂SiCH/HSiCH₂/SiCH₃ + H和H₂SiC/HSiCH/SiCH₂ + H₂。除了反应产物的子离子和同位素变体外，在m/z = 43处观察到的物种归属于产物H₂SiCH/HSiCH₂/SiCH₃，在m/z = 42处观察到的物种归属于产物H₂SiC/HSiCH/SiCH₂。在m/z = 41处观察到的信号归因于这两种类型的硅碳氢化物的解离电离。我们报告了特定实验室角度下产物的飞行时间谱和理论模拟结果，由此推导出质心坐标系中产物的动能分布和角分布。这两个反应的动能释放对散射角的依赖性较弱。失去H和H₂的通道分别释放平均平动能10.5和16.7千卡·摩尔⁻¹。由于分解前的氢转移很容易发生，产物H₂SiCH/HSiCH₂/SiCH₃和H₂SiC/HSiCH/SiCH₂分别表现出轻微的向前/向后偏好和各向同性的角分布。我们估计这些失去H和H₂的通道的分支比约为6:4。产物动能释放和电离阈值的测量表明，SiCH₃((²A″))和SiCH₂((³A₂))在异构产物中占主导地位。为了探索反应机理，我们计算了反应C((³P)) + SiH₄的势能面。最可能的机理是原子C(³P)在入口通道中插入SiH₄的Si - H键，随后反应复合物H₃SiCH异构化为HSiCH₃，接着分解为SiCH₃((²A″)) + H和SiCH₂((³A₂)) + H₂。我们没有观察到反应C((¹D)) + SiH₄的明显证据。
