8.5~12.5eV能量范围内溴甲苯离子的解离动力学研究

Dissociation dynamics of o-,p-,m-C_7H_7Br^+ ions in the 8.5～12.5eV energy range

利用同步辐射阈值光电子光离子符合成像质谱仪,开展了溴甲苯分子及其同分异构体(o-,p-,m-C7H7Br)的阈值光电子谱、阈值光电子光离子符合质谱和具有质量选择的符合光谱等实验研究,精确测量了溴甲苯分子的电离能,获得了C7H7+碎片离子的出现势,并且结合平动能和理论计算分析研究了o-,p-,m-C7H7Br+离子的解离动力学.结果表明,当离子内能不是很高时,溴甲苯离子将通过异构化反应过程解离生成溴原子和苯甲基碎片离子;而随着离子内能的增加,溴甲苯离子将直接解离生成甲苯基碎片离子.

The photoionization and dissociative photoionization of o-,p-,m-bromotoluene were investigated by utilizing synchrotron-based threshold photoelectron photoion coincidence spectroscopy(TPEPICO).Threshold photoelectron spectra(TPES),TPEPICO mass spectra and mass-selected TPEPICO spectra corresponding to each species were measured in the 8.5~12.5 eV energy range.The fundamental data including the ionization energy of bromotoluene molecules and the appearance energy of the C 7H 7+fragment ions are acquired and agree well with previous literature results.Then based on the obtained average kinetic energy released in the dissociation and the existing potential energy surfaces,the dissociation mechanisms of o-,p-,m-bromotoluene ions are proposed.The bromotoluene ions with small internal energy will dissociate to benzyl ions and Br atoms after performance of inter-conversion to isomers,whereas those with large internal energy will directly fragment to the tolyl ions via the C-Br bond breaking.