Fully Relativistic Theoretical Study On The Electron-Ion Impact Excitations

Electron scattering from a charged ions plays a very important role in the modeling and diagnostics of astrophysical and laboratory plasmas, as well as in the development of x-ray laser schemes. Recently, a fully relativistic distorted-wave method and computational procedure have been developed by our research group, which is based on the MCDF method and corresponding program packages GRASP92 and RATIP. In this methods, by using the Multi-configuration Dirac-Fock wave functions to describe the target-ion states, and the relativistic continuum wavefunctions to describe scattering electron states, the contributions of relativistic and correlation effects on collision strengths and rate coefficients are included automatically in the calculations. The contributions from Breit interaction are calculated in the low-frequency limit by diagonalizing the Dirac-Coulomb-Breit-Hamiltonian matrix. Using the above methods, the following contents are studied:Firstly, a systematical calculations on the energy levels of the 2s22p6, 2s22p5nl ,and 2s2p6nl (n=3,4; l=s,p,d,f) configurations and transition probabilities among those levels are calculated for neon-like ions from Z=21-92, by using the MCDF method. Based on the systematic calculations, all possible energy-crossings among the same JP level groups have been presented along the whole isoelectronic sequence. In addition, the effects of energy-crossing on transition probabilities and wavefunctions are analysised.Secondly, we study the electron impact excitations for neon-like FeXVII. It is found that the correlation effects are very important for the cross sections of neon-like FeXVII, when much more correlations are considered, the lower values of cross section will be obtained and which is agree with experimental results. For the low energy collisions, the convergent results can be obtained rapidly with small partial waves, but high partial waves must be considered for high energy collisions.Thirdly, as is well known, the DW method can not treat the resonance contributions. To remedy this limitation, the effects of resonance contributions are treated as a two-step process in the independent-processes isolated-resonance approximation. The contributions of resonance excitation (RE) to total cross sections and rate coefficients are studied for neon-like FeXVII. It is found that the resonance contributions are very significant for total cross-sections, they increase the direct excitation (DE) cross sections by 1-2 orders of magnitude near threshold. The RE contributions to the rate coefficient are also significant. For both the E1 resonance and forbidden transitions, the resonance contributions are quite large at temperatures below that of the biggest RE rate coefficient. With increasing of temperature, the RE contributions will diminish for E1 resonance transition at high electron temperatures. So RE contributions are more important for E1 forbidden transitions than for the allowed transitions. Even at high temperatures, the rate coefficient can be enhanced by a factor of 1-3 for the E1 forbidden transitions.Fourthly, using the MCDF method, we calculate systematically the energy levels of the 3s22p63d10, 3s23p63d94l, 3s23p53d104l and 3s3p63d104l (l=s,p,d,f) configurations and all transition probabilities among those levels for nickel-like ions from Z=31-92. Based on the calculations, the two types of two-electron and one-photon (TEOP) transitions are studied for nickel-like ions. Also all energy-crossing is presented. It is found that the TEOP transitions are very sensitive to the correlation of electrons, and the probabilities will be enhanced sharply in some special Z regions due to energy crossing along the sequence.Finally, we study the contributions of Breit interaction to the collision strengths, and the effects of strong configuration interaction (CI) on the cross sections for highly charged Nickel-like Gd36+, Rn58+-U64+(Z=86-92)ions. Also the behavior of cross sections with the atomic number Z is studied for the strongest 4d-4p (J=0-1) X-ray laser transitions. It is found that the contributions of Breit interaction to collision strengths depend intensively on the target ions. With the increasing of nuclear charge number Z of target ions, the contributions of Breit interaction will become more and more important. It is about 0.1-30% for the most of transitions from the ground state, and is nearly 50% for some special one in nickel-like U64+ ion. The strong CI also affects the collision strengths, which makes it increasing or decreasing suddenly at some special Z regions with energy-crossing occurred.