飞行时间质谱中的空间电荷效应研究

在分子多光子电离实验中, 发现母体离子的飞行时间(TOF)质谱峰随激光强度的提高而展宽, 此现象归因于离子团内离子间库仑排斥作用的空间电荷效应. 为从理论上解释此现象, 尝试了从一个简单的理论模型进行推演, 得到飞行时间质谱峰的半高全宽(FWHM)与激光能量、样品气体的分压比、电极板的总电压、离子质量及所采用的透镜聚焦焦距之间关系的解析表达式, 所得的结果能够很好地说明实验现象.

An Investigation on Space-charge Effect in the Time-of-flight Mass Spectrometry

In the multi-photon ionization experiment, the parent ion peak of time-of-flight (TOF) was observed to become broader with increasing laser power. Briefly, this phenomenon is caused by the space-charge effect of ions. A qualitative theoretical model, that the ion cloud created by the laser has a spherical form and the initial charge distribution is Gaussian, is used to evaluate the full width at half maximum (FWHM), which depends on the laser intensity, the pressure of the sample gas, the extraction electric field, the ionic mass, and the focal length of the lens employed. The proposed model agrees well with the experimental data.