Theoretical Investigation On Photoionization And Relevant Processes Of Atoms

The photoionization and relevant radiative recombination (RR) as well as radiative electron capture (REC) process are the fundamental interaction processes in the collision between particles (photo, electron and ions) and atoms. It has long been considered as one of the most interested topics of atomic physics. In the thesis a computer program package RERR08 has been developed for the investigation on the photoionization and relevant atomic process based on the Multi-configuration Dirac-Fock method. By using RERR08 program, the effects of the relativistic and multipole as well as electron correlation on the cross section of the photoionization process has been investigated. Meanwhile, RR and REC process also has been studied based on the same package.The relativistic effects become more important with the increasing of the nuclear charge number. For the different ns orbital of hydrogen-like ions, the relativistic effects increase in the binding energy and the mean radii of orbital is not a monotonic function of n. For the photoionization process of Li-like Fe²³⁺, the relativistic effects are more important in higher photo energy than in lower photo energy. For the photoionization of different subshell of specific ions, the photoionization cross section of inner subshell is less than that of outer subshell. It is means that the electron in outer subshell is easier to be ionized than the electron in inner subshell. For the cross section of the same subshell but different ions, it decreased with the increasing of nuclear charge Z at the same photo energy. Additional, the result in this thesis implies that the multipole effects is nonnegligible for the theoretical investigation on the photoionization with high photo energy and highly ionized target ions.Due to the electron correlation effects, once the electron of inner subshell has been ionized, the charge density distribution of the residual ions has been changed suddenly. It will lead to the orbital relaxation effects. In this thesis, it is shown that the relaxation effects are the main reason of the shake-up/conjugate shake-up processes accompanying with the inner-subshell photoionization. It is possible to reproduce the experimental spectrum of the shake-up process of 5s→6s accompanying with the 3d photoionization of Sr I and the shake-up/conjugate shake up process of 3s→nl accompanying with the 2p photoionization of Na I by considering the non-orthogonality of single electron orbital caused by the relaxation effects appropriately.The RR and REC processes, as an inverse process of photoionization process, has also been studied in the thesis. It has been shown that the cross section of an electron with specific kinetic energy and angular momentum has been captured into the outer-subshell of the highly charged He-like Fe²⁴⁺ ions was less than that of inner-subshells. Once the precise RR cross section was obtained, the REC cross section can be obtained by considering the momentum distribution of bound electron in target atoms/molecule. In this thesis, the REC process of H-like U⁹¹⁺ ions with N₂ molecule has been studied. If the transverse momentum distribution of the electrons in the initial state is neglected, the distribution of electron momentum in N₂ molecule can be represented by simple Compton profile. In present work, the experimental spectrum was reproduced very well by convoluted the corresponding RR cross section with Compton profile and include the Doopler effects due to the experimental consideration.The result from the existed study indicate that the further development and improvement of RERR08 package will be helpful to carry out further investigation, such as angular distribution and polarization, resonance structure and interference effects, giant resonance, the cascade radiative/radiativeless decay spectrum as well as the photoionization and RR process in plasma environment.