The R-matrix Studies On The Photoionizations Of Atoms And Ions

Photoionization is the one of the main process when photon interacts with atoms and ions. Studying photoionization of atomic systems provides the opportunity to investigate the dynamic interplay among many-body electron-electron correlations and relativistic effects. The data on the cross sections or related quantities for photoionization processes are eagerly needed in many fields of application such as astrophysics, atmospheric science, plasma science, radiation physics and chemistry, etc.The photoionization of atoms and ions are studied theoretically by using the R-matrix method in this thesis. The following is the main contents of the present thesis:1. There exist notable discrepancies with regard to the resonance structures when compared previous theoretical calculations with recent absolute experimental measurements for some Be-like and B-like ions. The photoionization cross section of Be-like ions N³⁺ and O⁴⁺ from the ground state 2s^{2 1}S and excited state 2s2p ³P°near the thresholds range are calculated using the R-matrix method. The resonance energies of 2pnp ³D,³S and 2pnd ¹P°Rydberg states are determined by analyzing the resonance structures of the photoionization cross sections. Detailed calculations are also performed on the photoionizations of the ground state 2s²2p ²P°and excited state 2s2p^{2 4}P of B-like ions N²⁺, O³⁺ and F⁴⁺. In photoionization cross sections of B-like ions we find resonances 2p²(³P)np ⁴D°,⁴P°for the first time. Our results show a good improvement in comparison with previous theoretical results.2. 25-state close-coupling calculations using the R-matrix method are carried out for the photoionization cross section of the ground state of Be atoms. The resonance energies of series 1s(2s2p ¹P3s)¹P°, 1s(2s2p ³Pns) ¹P°(n=5-I2) and 1s(2s2p ³Pnd)¹P°(n=5,6) are obtained from the photoionization cross sections. Present values are higher no more than 0.15 eV when compared with experimental results.3. Detailed 28-state close-coupling calculations based on an R-matrix formalism have been carried out to investigate the K-shell photoionization cross sections from the states 1s²s²2p ²P°, 1s²2s2p^{2 4}P,²D,²P,²S and 1s²2p^{3 4}S°of B-like Câ…¡ions. Emphasis is laid on analyzing the 1s—2p resonances and on obtaining the resonance energies, widths of the core-excited states and the oscillator strengths of the 1s—2p transitions. The calculated resonance energies, autoionization widths are compared with existing experimental and theoretical results. Rather good agreement is found between our results and other experimental and theoretical results, but for autoionization widths there remain some differences. The present numerical values may help the analysis of astrophysical and laboratory plasmas. 4. The photoionization cross section of the ground level (3s^{2 1}S₀) of atomic magnesium has been studied theoretically in the energy region between the Mg⁺(3s) and Mg⁺(3p) threshold using both the relativistic and nonrelativistic R-matrix method. Our results show that even for the intermediate-Z elements, the relativistic effects (mainly the spinorbit interactions) should not be neglected. The relativistic effects result in more extensive resonance structures due to many more coupled channels and different positions of resonances. The positions and widths of resonances have also been obtained and compared with a recent experiment. Excellent agreement is shown between our relativistic calculations and experimental measurements. In the present calculations, five Rydberg series of doubly excited states have been exhibited, i.e., 3pns ¹P, 3pnd ¹P, 3pns ³P, 3pnd ³D and 3pnd ³P, where the 3pnd ³P are found as the new fifth series.