Low Energy Electron/Positron-Atom/Molecule Scattering With Close-Coupling And R-Matrix Methods

Electron scattering, one of the fundamental processes in atomic and molecular physics, plays an important role in plasmas physics, atmospheric physic, radioactive physics, astrophysics and so on. This dissertation concentrates on the theoretical studies on electron/position-atom/molecule scattering with Close-Coupling and R-Matrix methods, which includes low energy electron/positron-hydrogen atom scattering in Debye plasma environments (or with screened Coulomb interaction), low energy electron-BH2 scattering, and the development of a multi-center theoretical method for electron-molecule impact ionization in the asymmetry geometry. The dissertation is organized as follows:The background of this dissertation, together with the typical theoretical methods for electron-atom/molecule scattering are introduced or summarized in Chapter 1.Positron-impact excitation of hydrogen atoms embedded in Debye plasma environments is investedgated in Chapter 2, which demonstrates that the screening interactions weaken the coupling between channels, resulting in the reduction of excitation cross sections from a few percentages to one magnitude of ten.The screening Coulomb interaction on electron-hydrogen atom scattering below the ionization threshold is studied in Chapter 3. We find that some Feshbach resonances would crossover into shape-type resonances with screening length decreasing, which brings in the dramatic effects in the excitation and elastic cross sections around the excitation threshold.Low energy electron-BH2 radical scattering is investegated in Chapter 4. The differential, integral and momentum-transfer cross sections for the rotationally elastic and inelastic scattering are reported in a 22-state molecular R-matrix method for the first time.A newly multi-center theoretical method for the fast electron-molecule impact ionization in the asymmetry geometry is developed in Chapter 5. The plane waves are applied to describe the incident and fast outgoing electrons, while the Schr?dinger equation with multi-center potential is solved to get the wavefunction of the slow ejected electron. The calculations for H2O molecules give the differential ionization cross sections in a good agreement with the experimental results.Finally, the conclusions and the research plans in future are given in Chapter 6.