Laser Induced Photoelectron Impact Ionization in Time-of-flight Mass Spectrometer

Multiple charged ions of Ar and NO were observed in MP1 experiment by 308nm excimer laser in time of flight mass spectrometer（TOF-MS）.FWHM of ion peak in time of flight mass spectra indicated that the ionization process was in a very short time scale（＜50ns）.Detailed analysis about the nascent spatial distribution of Ar ions indicated that the ions were continuously distributed between the repeller plate and the extractor grid.A delayable pulsed accelerating filed was used to investigate the ionization process.The result of delay experiment showed clearly that no ion was produced when arrival of the pulsed accelerating filed was only 0.2μs after arrival of the laser beam. Photoemission electrons, ejected from the extractor grid surface under irradiation of a laser beam,were suggested to play an important role in the ionization process. Electrons were accelerated by the electric filed between the repeller plate and the extractor grid and ionized the gas species in the way. MPI or LDI process were completely ruled out.