Certain Molecular Superexcited States And The Generalized Oscillator Strength

In this dissertation, using angle-resolved fast-electron-energy-loss spectrometer, some superexcited states of NO and N₂, as well as generalized oscillator strengths for the valence shell excitations of O₂ and N₂O, were studied. It is elucidated that this is one of the important methods to investigate the structures of superexcited states. In addition, it is also elucidated that the study of the generalized oscillator strengths of some molecules can provide rich information on the avoided crossing of potential curves and the anomalous behavior of intensity distribution within a vibrational progression.In chapter 1, the principle and structures of angle-resolved fast-electron-energy-loss spectrometer, as well as the basic conception of optical oscillator strength, generalized oscillator strength, and differential cross section, are described. Then, the gas mixture method for measuring the generalized oscillator strength is described briefly. Finally, the basic conception of molecular superexcited states, and the main experimental methods for investigating molecular superexcited states are introduced.In chapter 2, the absolute double differential cross section spectra of NO below 135 eV and in the scattering angle range of 0°-8° with an interval of 2° were determined with an incident electron energy of 2500 eV and an energy resolution of 100 meV. A vibrational resolved doubly excited state was measured for the first time. Furthermore, an inner-valence excited state was also measured, and the generalized oscillator strength of the inner-valence transition was calculated. In addition, the present measured features and those unassigned ones in the fluorescence spectra [Chem. Phys. 293, 65(2003)]were assigned based on the present experimental work and theoretical analysis.In chapter 3, the absolute optical oscillator strength density and generalized oscillator strength densities of N₂ below 100 eV and in the scattering angle range of 0°-6° with an interval of 2° were determined with an incident electron energy of 2500 eV and an energy resolution of 100 meV. The absolute generalized oscillator strengths for two transitions to the superexcited states at 23 and 31.4 eV were reported. More specifically, the generalized oscillator strengths for the transition to the superexcited state at 23 eV were obtained for the first time, and its momentum transfer dependence behavior was discussed.In chapter 4, the generalized oscillator strengths and the generalized oscillator strength ratios in the large K² region of 0.07-4.04 a.u. for the valence excitations of O₂ were investigated with an incident energy of 2500 eV and an energy resolution of 100 meV. The gas mixture of He and O₂ with a fixed proportion was used in the present experiment. The...