Study On The Interaction Between Atoms And Photon Or Electron In Plasma

The interactions between atoms and photon or electron are involved in some basic physics processes in plasma, such as photon radiative absorption, electronic transport and so on. By using the close-coupling R-matrix method, the interactions between atom and photon also atom and slow electron are studied, including the electron scattering cross sections and the photodetachment (or photoionization) cross sections. For low-Z elements, the non-relativistic R-matrix method can give fairly good prediction compared with experimental result. For high-Z elements, however, the relativistic effects influence the resonance structure near threshold very much. For more accurate theoretical calculation on electron scattering and photodetachment (or photoionization) cross section, the relativistic effects much be considered.The photoionization cross sections of nitrogen atom are studied by using the non-relativistic R-matrix method. The core-valence electron correlations are included in the calculation and fairly good photoionization cross sections are obtained compared with experimental results. One of the Rydberg 2s2p3? 5So ? np? 4P autoionization resonance states,?2s2p3? 5So ?3p?4P,?is?compared?with?the?experimental?result?and?discussed?in?detail.?For?high‐Z?elements,?the?photodetachment?cross?sections?of?negative?barium?ion?‐?which?is?focused?widely?because?of?the?stable?negative?ion?formed?by?a?closed?shell?obtaining?an?extra?electron,?and?negative?iodine?ion,?are?studied? by? using? the? fully? relativistic? R‐matrix? method.? At? the? same? time,? the?electron?scattering?cross?sections?from?barium?and?iodine?atom?are?given?in?the?same?theoretical?scheme.?For?the?photodetachment?process?of?negative?barium?ion,?the?spin‐orbital?splitting?of?the?electron?affinity?of?Ba—6s26p 2P3/2 and Ba—6s26p 2P1/2 is 57 meV, very close to the experimental result of 55 meV. The results show that, after considering the relativistic effects, the photodetachment cross sections of Ba- near threshold predict an obvious spin-orbital splitting of the resonance structure, which can't be obtained by the non-relativistic method. The total photodetachment cross sections dependent on temperature, which is important for a quantitative comparison between theory and experiment, are also given in the present thesis. In the study on the electron scattering from barium atom, the resonance structure near threshold also shows apparent relativistic splitting. For collision energies above 1.5 eV, both the present fully relativistic R-matrix and the former non-relativistic R-matrix results are almost twice of the experimental results. More precise experimental results or theoretical calculation are required to clarify the discrepancy between experiment and theory. As for the photodetachment process of I-, after considering the relativistic effects and electron core-valence correlation, the calculated photodetachment cross sections near threshold agree with the experimental results very well. But after the photon energies of 5 eV, both the present fully relativistic R-matrix results and former other theoretical results are lower than the experimental results. We suggest that the proposed autoionization resonance structure near 5.5 eV in the experimental results might come from other physics process in the CsI gas used in the experiment. The electron scattering cross sections from iodine atom give structures similar to that from heavy rare gas and heavy alkaline-earth metal elements.When the photon interacts with two atoms close to each other, the interference effects might occur to the outgoing electron, which is similar to the Young's two-slit interference experiment. Based on the calculated valence photoionization cross section of atomic nitrogen, the interference effects are studied between two neighboring nitrogen atoms. It is found that when the distance between the two atoms is close to that of the nitrogen molecule, leading the valence electrons of the atomic nitrogens forming a bonding, the interference effects from two centers can't be used to explain the photoionization cross section of the nitrogen molecule. But when the distance of the two atoms gets bigger, the interference effects should have influence on the total photoionization cross section of these two atoms. Because at that time, the valence electrons no longer form a bonding while these two atoms can't be treated as two independent atoms. The results show that when the energy of the outgoing electron is relatively small, because of the interference effects, the oscillate amplitude is big and the total cross sections of the two atoms are almost twice of the sum of that of the two independent nitrogen atoms. As the increasing of the energies of the outgoing electron, the oscillate amplitude of totals cross section caused by interference effects decreases and disappears at last. The total cross sections then are the same as twice of that of single nitrogen atom. When the distance between two nitrogen atoms gets bigger, the oscillate amplitude of totals cross section caused by interference effects decreases and disappears at last, too.In high and dense plasma, the distance of two particles usually makes them shouldn't be simply treated as two independent particles. The interference effects will occur during the photoionization process. When the radiative opacityof the plasma is dominated by bound-free photon absorption, the interference effects may influence the opacity of plasma. Taking the aluminum plasma with temperature of 50 eV and four different densities as example, the opacity of plasma is calculated considering interference effects by using a modified average-atom (AA) model. The distance distribution of two ions in plasma is simulated by Monte Carlo method. Based on the distance distribution obtained by Monte Carlo simulation, the opacity of the plasma is obtained by applying the interference formula for the two neighboring atoms photoionization cross section. With the same temperature, the results show that when the densities are relatively low, the interference effects have almost no influence on the radiative opacity; while the densities are getting higher, the influence is increasing. Whether the influence on the radiative opacity of plasma is constructive or deconstructive interference depends on the interference factor, which is decided by the distance between two ions and the momentum of outgoing electron together.