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Study of atomic and molecular many- body processes in astrophysics a thesis submitted for the degree of Doctor of Philosophy in Bangalore University, Bangalore


Study of atomic and molecular many- body processes in astrophysics a thesis submitted for the degree of Doctor of Philosophy in Bangalore University, Bangalore [Ph.D Thesis] Sonjoy Majumder - Bangalore Indian Institute of Astrophysics 2001 - xvi, 134p.

Thesis Supervisor B. P. Das

Atomic and molecular processes in astronomical objects have profound implications. Many of those objects in which certain atomic and molecular species have been detected are the sites for evolution of stellar envelopes and star formations. Measurements of atomic and molecular line intensities are powerful diagnostic tools for the exploration of many astrophysical processes. Accurate calculations of energy levels,
lifetimes of states, oscillator strengths and shapes of the atomic and molecular transition lines are often necessary to understand those processes. Rigorous treatments of atomic and molecular many-body effects are necessary for accurate calculations of these quantities. Such calculations have become important with the advent of high resolution spectrographs used in several ongoing missions for solar and stellar projects. Even improved experimental data are not adequate for them. Forbidden lines, which is one of the important features in this thesis work, are difficult to measure. Here we have employed various many-body approaches to calculate electronic properties of some atoms, ions and molecules which have astrophysical importance. Both non-relativistic and relativistic studies have been performed using perturbative and non-perturbative approaches. Effective valence shell Hamiltonian (HV) theory, one of the most advanced nonrelativistic approaches to multireference many-body perturbation theory (MBPT) is used to calculate binding energies (energy relative to first ionization threshold), excitation energies, oscillator strengths and transition probabilities of neutral carbon and calcium. The same method is used for calculating ground state energy difference between the cyclic and linear isomers of propynlidyne (C3H), as well as their harmonic vibrational frequencies, ionization potentials, electron affinities, excited state energies, dipole moments and oscillator strengths, some of which have not been reported before. One of the most important forbidden transitions, magnetic quadrupole transitions for Be-like ions are calculated using the multiconfiguration Dirac-Fock met.hod, which is a self consistent variational relativistic many-body method. The leading relativistic correction to the Coulomb interaction known as the Breit interaction is included in these calculations using first-order perturbation theory. The \v('ak allowed transitions of Mg II are accurately computed using one of the most powerful non-perturbative size-extensive approaches, the coupled cluster (CC) method. A new approach to generate the Dirac-Fock (DF) orbitals using finite basis set expansions is developed. These DF orbitals are used in the CC calculations to achieve high accuracies for various electronic properties of atoms.

Atomic Properties
Atomic Systems

043:52 / MAJ

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