Dissociative photoionization of methyl chloride studied with threshold photoelectron-photoion coincidence velocity imaging.
Dissociative photoionization of methyl chloride studied with threshold photoelectron-photoion coincidence velocity imaging.
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DOI：
10.1063/1.3676411
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发表时间：
2012-01
期刊：
影响因子：
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通讯作者：
Xiaofeng Tang;Xiaoguo Zhou;Manman Wu;Shilin Liu;Fu-yi Liu;Xiaobin Shan;Liu-si Sheng
中科院分区：
文献类型：
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作者：
Xiaofeng Tang;Xiaoguo Zhou;Manman Wu;Shilin Liu;Fu-yi Liu;Xiaobin Shan;Liu-si Sheng
利用阈值光电子-光离子符合(TPEPICO)速度成像技术，在11.0-18.5 eV的激发能范围内研究了态选择的CH(3)Cl(+)离子的离解。记录了CH(3)、Cl(+)(A(2)、A(1)和B(2)E)解离的CH3(+)离子的TPEPICO飞行时间谱和三维时间切片速度图。在本能量范围内，CH(3)(+)仍是最主要的碎片离子，而CH(2)Cl(+)碎片的支化率很低。对于CH(3)Cl(+)(A(2)A(1))离子的解离，在CH(3)(+)图像中清晰地观察到一系列同心环，这被认为是对CH(3)(+)离子伞状振动的激发。此外，各向异性参数对CH(3)(+)(1(1)A‘)的振动态的依赖关系提供了沿着C-Cl键断裂的浅势垒的直接实验证据。对于CH(3)Cl(+)(B(2)E)离子，CH3(+)(+)碎裂释放的总动能分布符合Maxwell-Boltzmann分布，表明从B(2)E态开始的Cl-损失路径是统计预解离。借助于计算的CH(3)Cl(+)(A(2)A(1))离子的氯离子损失势能曲线，CH(3)Cl(+)(A(2)A(1))离子形成的CH(3)(+)是一种快速的直接碎裂，而CH(3)Cl(+)(B(2)E)离子通过内转换到X(2)E的高振动态而统计地解离为CH(3)(+)+Cl。
Utilizing threshold photoelectron-photoion coincidence (TPEPICO) velocity imaging, dissociation of state-selected CH(3)Cl(+) ions was investigated in the excitation energy range of 11.0-18.5 eV. TPEPICO time-of-flight mass spectra and three-dimensional time-sliced velocity images of CH(3)(+) dissociated from CH(3)Cl(+)(A(2)A(1) and B(2)E) ions were recorded. CH(3)(+) was kept as the most dominant fragment ion in the present energy range, while the branching ratio of CH(2)Cl(+) fragment was very low. For dissociation of CH(3)Cl(+)(A(2)A(1)) ions, a series of homocentric rings was clearly observed in the CH(3)(+) image, which was assigned as the excitation of umbrella vibration of CH(3)(+) ions. Moreover, a dependence of anisotropic parameters on the vibrational states of CH(3)(+)(1(1)A') provided a direct experimental evidence of a shallow potential well along the C-Cl bond rupture. For CH(3)Cl(+)(B(2)E) ions, total kinetic energy released distribution for CH(3)(+) fragmentation showed a near Maxwell-Boltzmann profile, indicating that the Cl-loss pathway from the B(2)E state was statistical predissociation. With the aid of calculated Cl-loss potential energy curves of CH(3)Cl(+), CH(3)(+) formation from CH(3)Cl(+)(A(2)A(1)) ions was a rapid direct fragmentation, while CH(3)Cl(+)(B(2)E) ions statistically dissociated to CH(3)(+) + Cl via internal conversion to the high vibrational states of X(2)E.