Electron Momentum Spectrometer With 2Ï€Angle Range And Electron Momentum Spectroscopy At High Momentum Region

As a powerful experimental technology, electron momentum spectroscopy (EMS) has beensuccessfully applied in exploring electron structures for atoms and molecules. The attractiveability of EMS lies on directly obtaining not only the binding energy spectra, but also themomentum distributions for individual orbitals of atoms or molecules. Up to now, EMS hassuccessfully provided detailed information on momentum distributions for plenty of smallmolecules in gas phase and tested the qualities of different theories. However, further applicationof EMS is largely limited by the low coincidence count rates and the poor energy resolution. Overthe last four decades, great efforts have been made for the improvement of detected efficiency. Inthe present work, a high-sensitivity angle and energy dispersive multi-channel EMS spectrometer(AEDMC-EMS) has been successfully constructed. The symmetric non-coplanar geometry isemployed. A newly designed double half wedge and strip anode position-sensitive detector(DH-WSA PSD) is equipped to detect the ionized and scattered electrons passing through a 90°sector, 2Ï€spherical electrostatic analyzer over azimuthal angle range of about 150°for each. Thedetection efficiency of the new (e, 2e) spectrometer has been increased by a factor of about oneorder as compared to the spectrometer of third generation. Meanwhile, the momentum range hasbeen increased to about 8.0 a.u. as compared to about 3.0 a.u. for the conventional spectrometer.By using the new spectrometer, EMS measurements on CO₂, CF4and Ar have been carried out.The dissertation includes seven chapters as following:The theoretical background of EMS and the development history of EMS spectrometer aresummarized in chapter 1.Chapter 2 describes the construction of the new spectrometer.Chapter 3 describes the process from online raw data to the EMS information by software.Chapter 4 describes the performance testing of the new spectrometer with passing energy 600eV. The energy and angle resolution of the spectrometer is determined to be about 1.8 eV andΔθ=0.8°,Δφ= 2.0°by the ionization of Ar3p orbital.Chapter 5 describes the energy resolution improvement of the spectrometer. By decreasingthe passing energy of energy analyzer from 600 eV to 200 eV, higher energy resolution 1.4 eV areobtained, and the angle resolution (Δθ= 0.8°,Δφ= 2.5°) are almost preserved. By using themonochromator to decrease the energy spread of the incident electron beam, better energyresolution 0.9 eV are obtained.The extensive experimental and theoretical investigation of outer- and inner-valence satellite states of CO₂are presented in chapter 6. Taking the advantage of the high sensitivity ofthe spectrometer, four main peaks and 12 shake-up satellite states are resolved. The assignmentsand pole strengths for these satellites are obtained by comparing the experimental momentumprofiles (XMP) with the calculated results. The experimental results are also compared with thepresent high accuracy SAC-CI general-R calculation. The assignments of satellites 4–8 which aredisputed between previous experiment results and theoretical calculations are clarified. Thesatellites 10 - 12 above the first double ionization threshold are assigned for the first time.Taking the advantage of the expanded momentum range of the spectrometer, the EMS studieson high momentum range are reported in chapter 7. EMS investigation on bond oscillation of 1t1,4t2and 1e orbitals of CF4are presented. All of the three molecular orbitals (MOs) can beapproximated by linear combinations of the F2p atomic orbitals (AOs). The observed XMPsdivided by the theoretical momentum profile (TMP) of the F2p AO, which is calculated withindistorted wave impulse approximation (DWIA) using B3LYP method and aug-cc-pVTZ basis, theinformation of bond oscillations are shown clearly. The electron momentum profile of Ar3p and 3sorbitals in high momentum region are also investigated by the spectrometer. By comparisonbetween experiment and theoretical calculations, the corresponding electron momentum profilenearby the nuclear are discussed.Finally, the works of the dissertation together with the further prospects of EMS aresummarized.