Theoretical Studies Of Photoionization And Electron Collision Scattering Cross Sections Of Atoms

Photoabsorption (including the photoexcitation and photoionization) and electroncollision scattering cross sections are the indispensable physical parameters in laserphysics, radiation physics, plasma physics, atmospheric physics and astrophysics.Using our modified Breit-Pauli R-matrix code, the photoionization cross sectionsof ground Na are calculated. Our calculated cross sections and minimum position in thelow photon energy range (5?13 eV) are in excellent agreement with the experimentalresults. In the high energy range, there is an abnormal bump in the experimental mea-surements, which is a long-standing experimental puzzle. It is interesting to note thatthere is also an absorption window in the photoabsorption (i.e. photodissociation) crosssections of Na2+ . Such absorption window provides an answer to the puzzle. Based onthe same target and orbital bases, we calculated the photoionization cross sections ofexcited Na. Our calculated branching ratios of the J-resolved partial cross sectionsare in good agreement with the recent measurements within the experimental uncer-tainties. The excellent agreement between our theoretical results and the experimentalresults demonstrates that both the electron correlations and the relativistic effects canbe treated adequately on equal footing by the theoretical method and modified codes.Using the partial wave method we calculated the scattering cross sections of Naimpacted by the low-energy electron. We studied the features of the partial wave scat-tering amplitudes. Using the modified R-matrix code we calculated the GOSs of He-lium impacted by the high-energy electron within the First Born Approximation. TheGOSD surfaces of 1S, 1P and 1D channels are calculated and tested stringently by therecent experiments. In addition to the low- and high-energy electron impact excitationcross sections, a scheme to calculate the cross sections in the entire incident energyrange is discussed.