Molecular collisional excitation in astrophysical environments and modeling the early universe
Walker, Kyle Matthew
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Molecular collisions play an essential role in fields such as astrophysics, chemical physics, combustion, fusion research, and plasma physics. Even though molecular excitation calculations are vital in determining particle velocity distributions, internal state distributions, abundances, and ionization balance in gaseous environments, both theoretical calculations and experimental data for these processes are lacking. In order to probe material in astrophysical environments such as nebulae, molecular clouds, comets, and planetary atmospheres, reliable molecular collisional data for a complete set of species is needed. Since this set of data does not exist, various approximations, such as collider-mass scaling, are used to approximate unknown rate coefficients. The current collider-mass scaling approach utilized in i.e., the Leiden Atomic and Molecular Database (LAMDA), however, is flawed and an alternate scaling technique based on physical and mathematical principles, reduced potential scaling, is presented. To accelerate explicit calculations of collisional data, particularly rovibrationally resolved cross sections and rate coefficients for systems of astrophysical interest, parallelized versions of the scattering codes VRRMM and TwoBC were developed. Calculations and either zero energy or reduced potential scaling have been performed for the systems CO-He, CO-H, H2O-H2, HF-H2, HF-H, and H2-H2. Furthermore, the chemical evolution of primordial species in the Recombination Era was modeled, and accurate non-thermal spectra of the molecules H2, HD, and H2+ were produced for a primordial cloud as it collapses into a first generation star. These first generation stars were analyzed for possible observables and evaluated for their detectability by current and future observational facilities, such as the James Webb Space Telescope.