Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui 230026, China.
J Chem Phys. 2012 Jan 21;136(3):034304. doi: 10.1063/1.3676411.
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.
利用阈光电离-光电子符合（TPEPICO）速度成像技术，研究了在 11.0-18.5 eV 的激发能范围内，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)离子解离的 CH(3)(+)的 TPEPICO 飞行时间质谱和三维时间切片速度图像。在当前能量范围内，CH(3)(+)保持为最主要的碎片离子，而 CH(2)Cl(+)碎片的分支比非常低。对于 CH(3)Cl(+)(A(2)A(1))离子的离解，在 CH(3)(+)图像中清楚地观察到一系列同心环，这被归因于 CH(3)(+)离子的伞振动的激发。此外，各向异性参数对 CH(3)(+)(1(1)A')振动态的依赖性为沿 C-Cl 键断裂的浅势阱提供了直接的实验证据。对于 CH(3)Cl(+)(B(2)E)离子，CH(3)(+)碎片的总动能释放分布呈现出近麦克斯韦-玻尔兹曼分布，表明从 B(2)E 态的 Cl 损失途径是统计预解离。借助于 CH(3)Cl(+)的 Cl 损失势能曲线的计算，CH(3)Cl(+)(A(2)A(1))离子中 CH(3)(+)的形成是快速的直接碎裂，而 CH(3)Cl(+)(B(2)E)离子通过内部转换到 X(2)E 的高振动态以统计方式解离成 CH(3)(+) + Cl。
