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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 + 的结构相对比较稳定
A series of protonated cluster ions (NH3) nH + were obtained by direct photon ionization and time of flight mass spectrometry with multi-photon ionization at 355 nm. NH3) nH2 +. The dissociation of protonated ammonia cluster ions during free flight was observed in a reflection time of flight mass spectrometry study, indicating that the protonated ammonia cluster ions generated under these experimental conditions are some metastable cluster ions. Analysis of the daughter ion yield gives the ion dissociation rate constant for the protonated cluster, which allows estimation of the lifetime of metastable cluster ions. The size of the cluster increased from n = 3 to 20, and its lifetime decreased from 21 ms to 12 0 μs, which was about two orders of magnitude smaller. The dissociation rate has a stepwise increase from n = 5 to 6 due to the relatively stable structure of the protonated cluster ion (NH3) 4 NH4 + of 5 ammonia