Dielectronic Recombination Calculations for Silicon-Like Ions and the S2+ Orion Nebula Abundance Conundrum
Date of Award
Doctor of Philosophy
Dr. Thomas W. Gorczyca
Dr. Nigel Badnell
Dr. Kirk Korista
Dr. Manuel Bautista
Atomic processes, plasma modeling, atomic data, MCHF method, Orion nebula, low-temperature dielectronic recombination
Modern astronomical spectroscopy and imaging data are of an unprecedented quality, and span the full electromagnetic spectrum. To take full advantage of these data and successfully model the physical conditions in and elemental abundances of astrophysical plasmas, an accurate and complete description of relevant atomic processes occurring in a wide range of cosmic environments is required. The primary focus of this project is to investigate one of the atomic processes, dielectronic recombination (DR), for the entire silicon-like isoelectronic sequence. Dielectronic recombination is generally the most important contribution to the total recombination rate of atomic ions. This study will serve as an important ingredient in determining chemical abundances of elements in collisionallyionized and photoionized plasmas and as a benchmark for measurements being carried out at national and international accelerator laboratories.
A perturbative, multi-configurational Breit-Pauli (MCBP) method, implemented within an atomic structure and collision code, AUTOSTRUCTURE, is used to compute DR and radiative recombination (RR) rate coefficients for the ground and metastable initial levels of silicon-like ions, relevant to astrophysical plasmas and terrestrial fusion plasmas. The theoretical results are also compared with available experimental results for specific ions and are found to be in overall good agreement. In addition, a multi-configurational Hartree- Fock (MCHF) method is implemented to determine the low-lying resonance positions of S+ that are crucial for determining (<104K) low-temperature DR rates of S2+ in the Orion Nebula. These rates are highly sensitive to the low-lying resonance energy positions. This work is a part of an assembly of a dielectronic recombination database required in the modeling of dynamic-finite density plasmas.
Kaur, Jagjit, "Dielectronic Recombination Calculations for Silicon-Like Ions and the S2+ Orion Nebula Abundance Conundrum" (2017). Dissertations. 3167.