Contraction of Reflection TOF Mass Spectrometer for Very High Ions

为了探测高质量的分子或分子团簇离子，研制了一台反射式飞行时间质谱仪。飞行时间测量系统分为三部分：（1）超声速喷管源;（2）激光电离区;（3）飞行时间漂移管和离子检测器。为了获得高质量分辨率和高电离效率，采用了多光子电离（MPI）方法，利用ArF准分子激光器对分子团簇离子，如苯和氨团簇进行了MPI探测。检测到高达60聚体的苯簇，其对应于质量数4，800。检测限由所用的多通道板检测器决定，而不是由反射器飞行时间质谱仪决定。为了实际检测更高的质量，转换倍增器类型的离子检测器是必要的。质谱分辨率高达2，500，通常为2，000。质量分辨率受准分子激光器的脉冲宽度（10 ns）的限制。采用脉宽较短的电离激光，可获得较高的质量分辨率。目前的MPI反射飞行时间质谱仪系统在质量分辨率和质量轴离子探测极限方面都是一流的。

A reflectron time of flight mass spectrometer has been constructed in order to detect molecular or molecular cluster ions of very high masses. The time-of-flight system is divided by three parts : (1) Supersonic nozzle source ; (2) Laser-ionization region ; (3) Time of flight drift tube and ion det ector. Multiphoton ionization (MPI) has been used in order to obtained high mass resolution and high ionization efficiency.Molecular cluster ions, such as benzene and ammonia clusters, are detected by MPI method using an ArF excimer laser. Benzene clusters as high as 60-mer are detected, which corresponds to mass number 4,800. The detection limit is governed by the multichannel plate detector used and not by the reflectron time of flight mass spectrometer. To actually detect higher masses a conversiondynode type ion detector is necessary. The mass spectral resolution is as high as 2,500 and typically 2,000. The mass resolution is limited by the pulse width of the excimer laser (10 ns). Higher mass resolution will be obtained by using an ionizing laser with shorter pulse width. The present MPI reflectron time-of-flight mass spectrometer system is the first rate in terms of the mass resolution and the ion detection limit in mass axis.