The Study Of Electron Impact Ionization Of Hydrogen Molecule And Helium

The electron impact ionization is one of the most fundamental physical processes in atomic and molecular physics. The information of either structures of the target or dynamics of the process can be extracted at different specific experimental conditions. In present thesis, electron impact ionization studies aimed to the knowledge on both above two respects have been dissertated in detail, which includes the vibrationally resolved electron momentum spectroscopy (EMS) study on hydrogen molecule (H2), and the ejected electron spectroscopy (EES) and the (e,2e) spectroscopy studies on the double excitation-autoionization dynamics of Helium. Six chapters are included as following:Chapter1introduces some basic knowledge about electron impact ionization studies. First, a brief theoretical background and technical progress of EMS are presented. Second, two types of parameterizations describing the He autoionizing profiles in electron impact spectra are introduced and discussed. Finally, the history and progress of different studies about He autoionization, employing electron energy loss spectroscopy, ejected electron spectroscopy and (e,2e) spectroscopy respectively, is summarized in detail.Chapter2provides a overview of the (e,2e) apparatus used in all experimental works of this thesis and the related experimental methods.A home-developed nonlinear fitting program based on Monte Carlo algorithm is introduced in Chapter3. The advantage of the program is illustrated with a example-the clarification of the ordering of outer valence orbitals of CF2Br2in peak fitting of low-resolution EMS experiment employing the program.A preliminary study of the vibrationally resolved EMS is reported in Chapter4. The vibrationally resolved electron momentum profiles of1sσg orbitals of H2have been obtained for the first time in experiment. The corresponding theoretical momentum profiles are also calculated for comparison. Furthermore, the contributions of different vibrational states to the electron momentum profiles of lsσg orbitals of H2are resolved in experiment by comparing of ratio of the profiles corresponding to different vibrational states of ion.In Chapter5, the autoionizing resonances (2s2)1S,(2p2)1D and (2s2p)1P of helium are investigated by ejected electron spectroscopy at incident energies of250-2000eV and ejected angles of26°～116°. Shore-Balashov parametrization is used to analyze the resonance profiles and a series of angular variations of direct ionization cross section and Shore parameters are obtained. Besides distinct oscillations of both obtained parameters with angles for all three resonances, the discrepancies between present results at250eV and that of McDonald and Crowe (200eV)[J. Phys. B25,2129(1992);25,4313(1992)] and Sise et al (250eV)[Phys. Rev. A84,022705(2011)], especially for1D and1P states, are also observed. In addition, the preliminary (e,2e) experimental study on the same resonances is also reported.Finally, the summarizations and the prospects are given in Chapter6.