应用反射式飞行时间质谱仪研究氨团簇离子解离动力学  

Kinetic Study of the Metastable Ammonia Cluster Ions Using Reflection Time-of-Flight Mass Spectroscope

作　　者：胡勇军[1] 王秀岩[1] 吕日昌[1] 

机构地区：[1]中国科学院大连化学物理研究所分子反应动力学国家重点实验室,大连116023

出　　处：《Chinese Journal of Chemical Physics》2000年第5期521-527,共7页化学物理学报（英文）

摘　　要：用直射式和反射式飞行时间质谱研究了氨分子团簇体系在 355nm激光下的多光子电离 ,得到一系列的质子化团簇离子 (NH3 ) nH+ ,同时还观察到超价氨团簇离子 (NH3 ) nH2 + 。在反射式飞行时间质谱研究中观测到质子化氨团簇离子在自由飞行过程中的解离现象 ,表明在该实验条件下生成的质子化氨团簇离子是一些亚稳态团簇离子。对子离子产率的分析 ,得到质子化团簇离子解离速率常数 ,从而可以估计亚稳态团簇离子的寿命。团簇尺寸从n =3增大到 2 0 ,其寿命从 2 1ms减小到 12 0 μs ,大约小了两个数量级。解离速率在n =5到 6有一个阶跃式上升 ,这是由于 5个氨组成的质子化团簇离子 (NH3 ) 4 NH4 +The multiphoton ionization of the ammonia clusters at 355nm was studied using both conventional and reflection time-of-flight mass spectrometers. Aseries of protonated ammonia clusters (NH 3) n H + were obtained,and the hypervalent ammonia cluster ions (NH 3) n H 2 +( n >2 ) were observed. The daughter ions which were produced from dissociation of the metastable ammonia cluster ions during their free flight were also observed. The dissociation rate constants were derived from the experimental result which depends upon the number of the ammnia molecules in a cluster ion. The life times of the metastable cluster ions were estimated, which range from 21ms to 122μs for different cluster size from n =3 to 20. The larger the cluster size, the faster the dissociation rate and the shorter of the life time of the cluster ions. The kinetics shows that with n =5 or smaller the cluster ions are more stable comparing to those with n ≥6, which is consistant with the observation reported in literature.

关 键 词：飞行时间质谱 亚稳态 氨团簇离子 解离动力学 

分 类 号：O657.63[理学—分析化学]