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Kinetic Study of the Metastable Ammonia Cluster Ions Using Reflection Time-of-Flight Mass Spectroscope
Hu Yongjun,Wang Xiuyan,Lv Richang
Author NameAffiliation
Hu Yongjun State Key Laboratory of Molecular Reaction Dynamics Dalian Institute of Chemical Physics Chinese Academy of Science, Dalian 116023 
Wang Xiuyan State Key Laboratory of Molecular Reaction Dynamics Dalian Institute of Chemical Physics Chinese Academy of Science, Dalian 116023 
Lv Richang State Key Laboratory of Molecular Reaction Dynamics Dalian Institute of Chemical Physics Chinese Academy of Science, Dalian 116023 
Abstract:
The multiphoton ionization of the ammonia clusters at 355nm was studied using both conventionaland reflection time-of-flight mass spectrometers. Aseries of protonated ammonia clusters(NH3)nH+were obtained,and the hypervalent ammonia cluster ions (NH3)nH2+(n>2 ) were observed. The daughter ions which were produced from dissociation of the metastable am-monia 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 fromn=3 to 20. The larger the cluster size, the faster the dis-sociation rate and the shorter of the life time of the cluster ions. The kinetics shows that withn=5 or smaller the cluster ionsare more stable comparing to those withn≥6, which is consistant with the observation reported in literature.
Key words:  TOF-MS, Metastable ammonia cluster ion, Dissociation
FundProject:
应用反射式飞行时间质谱仪研究氨团簇离子解离动力学
胡勇军,王秀岩,吕日昌
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20,其寿命从21ms减小到120μs,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)4NH4+的结构相对比较稳定。
关键词:  飞行时间质谱  亚稳态  氨团簇离子  解离
DOI:10.1088/1674-0068/13/5/521-527
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