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. 2013 Mar 7;138(9):094306. doi: 10.1063/1.4792368.
Dissociation of internal energy selected CF4(+) ions in an excitation energy range of 15.40-19.60 eV has been investigated using threshold photoelectron-photoion coincidence (TPEPICO) velocity imaging. Only CF3(+) fragment ions are observed in coincident mass spectra, indicating all the X(2)T1, A(2)T2, and B(2)E ionic states of CF4(+) are fully dissociative. Both kinetic energy released distribution (KERD) and angular distribution in dissociation of CF4(+) ions have been derived from three-dimensional TPEPICO time-sliced images. A parallel distribution of CF3(+) fragments along the polarization vector of photon is observed for dissociation of CF4(+) ions in all the low-lying electronic states. With the aid of F-loss potential energy curves, dissociation mechanisms of CF4(+) ions in these electronic states have been proposed. CF4(+) ions in both X(2)T1 and A(2)T2 states directly dissociate to CF3(+) and F fragments along the repulsive C-F coordinate, while a two-step dissociation mechanism is suggested for B(2)E state: CF4(+)(B(2)E) ion first converts to the lower A(2)T2 state via internal conversion, then dissociates to CF3(+) and F fragments along the steep A(2)T2 potential energy surface. In addition, an adiabatic appearance potential of AP0(CF3(+)∕CF4) has also been established to be 14.71 ± 0.02 eV, which is very consistent with the recent calculated values.
已使用阈值光电离-光电离符合（TPEPICO）速度成像研究了在 15.40-19.60 eV 的激发能范围内的内部能量选定的 CF4(+)离子的离解。在符合质量谱中仅观察到 CF3(+)碎片离子，表明 CF4(+)的所有 X(2)T1、A(2)T2 和 B(2)E 离子态均完全离解。从三维 TPEPICO 时间切片图像中得出了 CF4(+)离子离解的动能释放分布（KERD）和角分布。在所有低电子态中，观察到 CF4(+)离子的 CF3(+)碎片沿着光子的偏振矢量呈平行分布。借助 F 损失势能曲线，提出了这些电子态中 CF4(+)离子的离解机制。X(2)T1 和 A(2)T2 态中的 CF4(+)离子直接沿着排斥 C-F 坐标裂解为 CF3(+)和 F 碎片，而 B(2)E 态则建议采用两步离解机制：CF4(+)(B(2)E)离子首先通过内转换转化为较低的 A(2)T2 态，然后沿着陡峭的 A(2)T2 势能面裂解为 CF3(+)和 F 碎片。此外，还建立了 AP0(CF3(+)∕CF4)的绝热出现电势，其值为 14.71 ± 0.02 eV，与最近的计算值非常吻合。
