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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Dissociative Photoionization of 1-Halogenated Silacyclohexanes: Silicon Traps the Halogen
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Dissociative Photoionization of 1-Halogenated Silacyclohexanes: Silicon Traps the Halogen

机译：1-卤代硅环己烷的解离光电离：硅陷阱卤素。

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The threshold photoelectron spectra and threshold photoionization mass spectra of 1-halogenated-1-silacyclohexanes, for the halogens X = F, Cl, Br, and I, have been obtained using synchrotron vacuum ultraviolet radiation and photoelectron photo ion coincidence spectroscopy. As confirmed by a similar ionization onset and density functional theory molecular orbitals, the ionization to the ground state is dominated by electron removal from the silacyclohexane ring for X = F, Cl, and Br, and from the halogen lone pair for X = I. The breakdown diagrams show that the dissociative photoionization mechanism is also different for X = I. Whereas the parent ions decay by ethylene loss for X = F to Br in the low-energy regime, the iodine atom is lost for X = I. The first step is followed by a sequential ethylene loss at higher internal energies in each of the compounds. It is argued that the tendency of silicon to lower bond angles stabilizes the complex cation in which C2H4 is eta(2)-coordinated to it, and which precedes ethylene loss. Together with the relatively strong silicon-halogen bonds and the increased inductive effect of the silacyclohexane ring in stabilizing the cation, this explains the main differences observed in the fragmentation of the halogenated silacyclohexane and halogenated cyclohexane ions. The breakdown diagrams have been modeled taking into account slow dissociations at threshold and the resulting kinetic shift. The 0 K appearance energies have been obtained to within 0.08 eV for the ethylene loss for X = F to Br (10.56, 10.51, and 10.51 eV, respectively), the iodine atom loss for X = I (10.11 eV), the sequential ethylene loss for X = F to I (12.29, 12.01, 11.94, and 11.86 eV, respectively), and the minor channels of H loss for X = F (10.56 eV) and propylene loss in X = Cl (also at 10.56 eV). The appearance energies for the major channels likely correspond to the dissociative photoionization reaction energy.
机译：卤素X = F，Cl，Br和I的1-卤代-1-硅环己烷的阈值光电子能谱和阈值电离质谱已使用同步加速器真空紫外辐射和光电子光子重合光谱法获得。正如通过类似的电离起始和密度泛函理论分子轨道所证实的那样，对于X = F，Cl和Br，从硅环己烷环中除去电子，对于X = I，从卤素孤对中除去电子至基态。分解图表明，对于X = I，离解性光电离机理也不同。在低能状态下，对于X = F到Br，母离子因乙烯损失而衰减，而X = I时碘原子损失了。在每个步骤中，随后是在较高的内部能量下乙烯发生连续的乙烯损失。有人认为，硅趋向于较低键角的趋势稳定了C2H4与eta（2）配位且在乙烯损失之前的复合阳离子。再加上相对较强的硅-卤素键和硅环己烷环在稳定阳离子中增强的感应作用，这解释了在卤代硅环己烷和卤代环己烷离子裂解过程中观察到的主要差异。击穿图已建模，考虑到阈值处的缓慢解离和所产生的动力学位移。对于X = F到Br（分别为10.56、10.51和10.51 eV）的乙烯损失，对于X = I（10.11 eV）的碘原子损失，连续的乙烯，获得的0 K出现能在0.08 eV以内。 X = F对I的损耗（分别为12.29、12.01、11.94和11.86 eV），X的H损耗的次要通道为F（10.56 eV），丙烯的X损耗为C = Cl（也为10.56 eV）。主要通道的出现能量可能对应于离解光电离反应能量。

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