The Study Of Electron-atom (electron-ion) Collision Cross Sections

The inelastic electron-atom (electron-ion) collisions are important processes in diverse fields such as radiation physics, plasma physics, atmospheric physics and astrophysics. The data of collision cross sections are the indispensable physical parameters, for example, which can be used to diagnose the nebulas and laboratory plasma.The combination of R-matrix methods and quantum defect theory can been proven to be a more efficient and accurate method to study the entire excitation processes of the fast electron-atom collisions as a whole. The high-energy electronic-impact excitation cross section is directly proportional to the generalized oscillator strength (GOS) of the target atom. The generalized oscillator strengths of helium atom from the ground state to the excited states (21S,21Pand 31D et al) are calculated using the updated R-matrix codes within the first Born approximation. Our calculation results are in good agreement with the previous theoretical and experimental results at high incident energies. In order to treat the bound-bound and bound-continuum transitions in a unified manner, the generalized oscillator strength density is defined. We calculate the generalized oscillator strength densities of 1S, 1Pand1D channels, namely the complete high-energy collision cross sections of electronic-impact excitations into all the n1S, n1Pand n1D excited states. In addition to high-energy excitation cross sections, a scheme how to calculate the excitation cross sections for entire incident energy range is discussed.