飞行时间质谱峰形分析

报道了在用脉冲355 nm的YAG激光对水/甲醇二元团簇的多光子电离飞行时间质谱研究中,发现在电离激光相对于脉冲分子束的不同延时或是同一延时下不同的激光能量下,测得的离子谱峰除强度变化外,峰值发生漂移.离子峰值漂移的大小与信号强度密切相关.信号强度越大,离子的飞行时间越短,峰值漂移越大.分析认为:这种峰值漂移不是因为新质量数谱峰的出现,而是离子在穿越质谱仪的离子引出区和加速区极板时发生部分离子吸附,引起极板间电压的起伏造成的.离子信号越强,意味着极板对离子吸附的量越大,导致离子峰值的漂移越大.离子在电场起伏下的数值模拟结果与实验中观测到的离子峰值漂移规律一致.

Analysis of the peak profile in time-of-flight mass spectrum

A new phenomenon is observed when we use YAG 355 nm laser to ionize water/methanol mixture molecular beam and detect the ions with time-of-flight mass spectrometer. The peaks position of mass ions shift when changing the laser delay time to the molecular beam or singly changing laser energy while keeping other conditions not changed. It can be determined by analyzing mass spectra that the peak's shift does not mean new ions appear.The reason is deduced to the voltage fluctuation on the extract electrode of TOF when ions passing through the grating electrode and parts of them are being absorbed. The ion's shift altitude is proportion with the ion's intensity,and the ion's total flight time is shortened with ion's intensity increasing. The numerical simulation of charged-particle's movement in electrical field also supports the deduction and is consistent with the experimental results.