二甲醚在13.30~14.30 eV激发能下的光电离解离研究  

Dissociative photoionization of dimethyl ether in the energy range of 13.3~14.3 eV

作　　者：徐磊[1] 吴向坤[1] 于同坡 周晓国[1] 刘世林[1] XU Lei;WU Xiangkun;YU Tongpo;ZHOU Xiaoguo;LIU Shilin(Hefei National Laboratory for Physical Sciences at the Microscale, and Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China)

机构地区：[1]合肥微尺度物质科学国家研究中心,中国科学技术大学化学物理系,安徽合肥230026

出　　处：《中国科学技术大学学报》2020年第5期629-636,共8页JUSTC

基　　金：国家自然科学基金(21573210,21873089)资助.

摘　　要：利用同步辐射真空紫外光电离结合阈值光电子-光离子符合质谱技术对二甲醚分子在13.30~14.30 eV激发能下的电离-解离动力学进行了研究.该能量范围内,二甲醚离子处于B^(2)B_(2)和C^(2)A_(2)电子态,且两态相互重叠,解离产物则主要有m/z=45、29和31三种离子碎片.通过扣除重叠的m/z=29碎片离子质谱,获得了可靠的m/z=31碎片离子的飞行时间质谱轮廓.在此基础上,通过拟合质谱峰型获得了该碎片的平动能分布.在低于14.00 eV的范围内,该碎片离子仅表现出单一的统计解离通道性质,而当激发能量高于14.00 eV时,解离机理发生了明显的改变,表现出双模分布的特征.结合实验测量的平动能分布和理论预测结果,提出了不同电子态二甲醚离子解离产生m/z=31碎片离子的途径:B^(2)B_(2)电子态的二甲醚离子主要通过氢迁移异构化为CH_(2)OHCH^(+)_(3)后解离生成CH_(2)OH^(+)(m/z=31)结构,而C^(2)A_(2)电子态则发生直接的C—O键断裂解离,生成高平动能分布的CH_(3)O^(+)(m/z=31)的碎片离子.Dissociative photodissociation of dimethyl ether in the photon energy of 13.30~14.30 eV was studied using threshold photoelectron photoion coincidence mass spectrometry,combined with photoionization using a vacuum ultraviolet light source from synchrotron radiation.In this range,the dimethyl ether ions in B^(2)B_(2) and C^(2)A_(2) states were prepared,and the main fragment ions were m/z=45,29 and 31.By subtracting the contribution of the m/z=29 fragment ions,the reliable time-of-flight profile of the m/z=31 fragment ions was obtained.Then the related kinetic energy distribution was derived from fitting the profile.Below 14.00 eV,a unique statistical dissociation was observed for the formation of the m/z=31 ions,while the dissociation mechanism was changed significantly to dual dissociation channels under the photon energy above 14.00 eV.Combined with the experimental kinetic energy released distribution and the theoretical predictions,an overall mechanism of dimethyl ether ions in B^(2)B_(2) and C^(2)A_(2) states to produce the m/z=31 ions was proposed.For dimethyl ether ions in B^(2)B2 state,the CH_(2)OH^(+)(m/z=31)fragment is produced via isomerization and statistical dissociation.For the C^(2)A_(2) state,dimethyl ether ions can directly dissociate to CH_(3)O^(+)(m/z=31)fragment ions with high kinetic energy by breaking C—O bond.

关 键 词：光电子-光离子符合 飞行时间质谱 解离动力学 反应机理 

分 类 号：O643.1[理学—物理化学]