The Electron Momentum Spectroscopy Study On Molecular Interference Effect And Molecular Vibrational Effect

Electron momentum spectroscopy (EMS) is a powerful experimental technology, which can directly probe the information of atomic and molecular orbital electron wavefunction. With its unique advantages, the multi-center interference effects and vibration effects of molecules can be investigated at level of the wavefunction. In present thesis, the three-center interference effect for the NF3molecule and the ring-puckering effect for oxetane molecule have been studied. Additionally, a new type wedge and strip anode with polar coordinate readout has been designed. Combined with micro-channel plates, a new two-dimensional position-sensitive detector is developed. Five chapters are included as following:Chapter1introduces basic knowledge about EMS, including the principle of (e,2e) reaction and the theoretical background. Furthermore, a brief summary of the EMS research progresses is given in this chapter.Chapter2describes the2π-angle (e,2e) electron momentum spectrometer, and introduces experimental methods and theoretical methods of EMS.In chapter3, a new type wedge and strip anode with polar coordinate readout has been designed. The parameter optimization and performance have been simulated out using numerical method. Combining the WSA with micro-channel plates, a new two-dimensional position-sensitive detector has been developed. Through the inelastic scattering experiment of Ar gas, its performance is tested, and a well performance is obtained. The results show that the new detector has good linearity and reasonable position resolution.The EMS of NF3has been studied using the2π-angle (e,2e) electron momentum spectrometer in chapter4. The binding energy spectra as well as electron momentum distributions for the outer-valence molecular orbitals are obtained. The experimental momentum distributions are compared with the theoretical ones calculated by Hartree-Fock (HF), density functional theory (DFT-B3LYP) and SAC-CI methods with6-311++G*and aug-cc-pVTZ basis sets. Three-center interference effect is observed for molecular orbitals1a2and4e. The distance between any two F atoms in NF3molecule RF-F is determined to be3.73a.u. by fitting the experimental data with interference factor, which is consistent with the experimental result of4.03a.u. obtained from electron diffraction.In chapter5, the binding energy spectra and electron momentum distributions for the outer-valence molecular orbitals of oxetane have been measured using (e,2e) electron momentum spectrometer with non-coplanar asymmetric geometry. The experimental momentum distributions were compared with the density functional theory calculations employing B3LYP hybrid functional with aug-cc-pVTZ basis set. It was found that the calculation at planar geometry (C2V) completely fails to interpret the large "turn-up" at low momentum region in electron momentum distribution of the highest occupied molecular orbital (HOMO)3b1, while calculations considering the thermally populated vibrational states of ring-puckering motion have significantly improved the agreement. The results indicate that the ring-puckering motion of oxetane has a strong effect on the electron density distribution of HOMO.