Contraction of Reflection TOF Mass Spectrometer for Very High Ions

为了探测高质量的分子或分子簇离子，建立了反射飞行时间质谱仪。飞行时间系统分为三个部分：(1)超音速喷管源；(2)激光电离区；(3)飞行时间漂移管和离子探测器。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）技术。利用ArF准分子激光，用MPI方法检测了苯和氨等分子簇离子。检测到的苯团簇最高为60 mer，对应质量数为4800。检测限由所使用的多通道板探测器决定，而不受飞行质谱仪反射时间的影响。要真正探测到更高质量的离子，转换型离子探测器是必要的。质谱分辨率高达2500，通常为2000。质量分辨率受准分子激光脉冲宽度（10ns）的限制。使用脉冲宽度较短的电离激光器可以获得更高的质量分辨率。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检出限方面都是一流的。

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.