Tang Xiaofeng, Garcia Gustavo A, Nahon Laurent
Synchrotron SOLEIL, L'Orme des Merisiers, St. Aubin BP 48, 91192 Gif sur Yvette, France.
J Phys Chem A. 2015 Jun 11;119(23):5942-50. doi: 10.1021/jp510319b. Epub 2015 Jan 12.
The dissociation of energy-selected methyl fluoride ion CH3F(+) along the CH3(+) and F formation channel has been investigated in detail in the 12.2-19.8 eV energy range. Three low-lying electronic states of the CH3F(+) ion, X(2)E, A(2)A1, and B(2)E, were prepared and analyzed by the method of double imaging photoelectron photoion coincidence (i(2)PEPICO). Three types of CH3(+) fragment ions corresponding to the dissociation of X(2)E, A(2)A1, and B(2)E electronic states have been observed and identified through their kinetic energy release distribution (KERD) curves, showing that the dissociation of the CH3F(+) ion in the different electronic states along the CH3(+) formation channel is state-specific, even outside of the Franck-Condon region. Highly excited vibrational levels of the X(2)E ground state can be populated through a resonant or near-resonant autoionization process and undergo vibrational predissociation into CH3(+) fragment ions. The A(2)A1 first excited state is repulsive along the F-loss coordinate, and its dissociation is direct and fast. The CH3F(+) ions in the B(2)E excited state first undergo an internal conversion toward the hot cation ground state X(2)E and then statistically dissociate into CH3(+) and F fragments.
在12.2 - 19.8电子伏特能量范围内，详细研究了能量选择的氟甲烷离子CH3F(+)沿CH3(+)和F形成通道的解离情况。采用双成像光电子光离子符合（i(2)PEPICO）方法制备并分析了CH3F(+)离子的三个低电子态，即X(2)E、A(2)A1和B(2)E。通过动能释放分布（KERD）曲线观察并识别了与X(2)E、A(2)A1和B(2)E电子态解离相对应的三种类型的CH3(+)碎片离子，表明CH3F(+)离子在不同电子态下沿CH3(+)形成通道的解离具有态特异性，即使在弗兰克 - 康登区域之外也是如此。X(2)E基态的高激发振动态可通过共振或近共振自电离过程填充，并经历振动预解离形成CH3(+)碎片离子。A(2)A1第一激发态沿F损失坐标是排斥的，其解离是直接且快速的。处于B(2)E激发态的CH3F(+)离子首先向热阳离子基态X(2)E发生内转换，然后统计解离为CH3(+)和F碎片。
