Hayakawa Shigeo, Kitaguchi Akihiro, Kameoka Satoko, Toyoda Michisato, Ichihara Toshio
Department of Chemistry, Graduate School of Science, Osaka Prefecture University, 1-1 Gakuencho, Nakaku, Sakai, Osaka 599-8531, Japan.
J Chem Phys. 2006 Jun 14;124(22):224320. doi: 10.1063/1.2204598.
Doubly charged tungsten hexacarbonyl W(CO)(6) (2+) ions were made to collide with Ar and K targets to give singly and doubly charged positive ions by collision-induced dissociation (CID). The resulting ions were analyzed and detected by using a spherical electrostatic analyzer. Whereas the doubly charged fragment ions resulting from collisional activation (CA) were dominant with the Ar target, singly charged fragment ions resulting from electron transfer were dominant with the K target. The internal energy deposition in collisionally activated dissociation (CAD) evaluated with the Ar target was broad and decreased with increasing internal energy. The predominant peaks observed with the K target were associated with singly charged W(CO)(2) (+) and W(CO)(3) (+) ions: these ions were not the result of CA, but arose from dissociation induced by electron transfer (DIET). The internal energy deposition resulting from the electron transfer was very narrow and centered at a particular energy, 7.8 eV below the energy level of the W(CO)(6) (2+) ion. This narrow internal energy distribution was explained in terms of electron transfer by Landau-Zener potential crossing at a separation of 5.9 x 10(-8) cm between a W(CO)(6) (2+) ion and a K atom, and the coulombic repulsion between singly charged ions in the exit channel. A large cross section of 1.1 x 10(-14) cm(2) was estimated for electron capture of the doubly charged W(CO)(6) (2+) ion from the alkali metal target, whose ionization energy is very low. The term "collision-induced dissociation," taken literally, includes all dissociation processes induced by collision, and therefore encompasses both CAD and DIET processes in the present work. Although the terms CID and CAD have been defined similarly, we would like to propose that they should not be used interchangeably, on the basis that there are differences in the observed ions and in their intensities with Ar and K targets.
使双电荷的六羰基钨W(CO)₆(2+)离子与氩气和钾靶碰撞，通过碰撞诱导解离（CID）产生单电荷和双电荷的正离子。使用球形静电分析仪对产生的离子进行分析和检测。当与氩靶碰撞时，碰撞活化（CA）产生的双电荷碎片离子占主导；而与钾靶碰撞时，电子转移产生的单电荷碎片离子占主导。用氩靶评估的碰撞活化解离（CAD）中的内能沉积范围较宽，且随内能增加而减小。用钾靶观察到的主要峰与单电荷的W(CO)₂(+)和W(CO)₃(+)离子有关：这些离子不是CA的结果，而是由电子转移诱导解离（DIET）产生的。电子转移产生的内能沉积非常窄，且集中在特定能量处，比W(CO)₆(2+)离子的能级低7.8 eV。这种窄的内能分布可以通过W(CO)₆(2+)离子与钾原子之间在5.9×10⁻⁸ cm的间距处通过朗道 - 齐纳势垒交叉的电子转移以及出射通道中单电荷离子之间的库仑排斥来解释。对于从碱金属靶捕获双电荷的W(CO)₆(2+)离子的电子俘获，估计其截面很大，为1.1×10⁻¹⁴ cm²，碱金属靶的电离能非常低。从字面上看，“碰撞诱导解离”一词包括由碰撞诱导的所有解离过程，因此在本工作中涵盖了CAD和DIET过程。尽管CID和CAD术语的定义相似，但基于用氩靶和钾靶观察到的离子及其强度存在差异，我们建议它们不应互换使用。
