Computational Electronic Spectroscopy Predictions for Astrochemical Ice Analogues and Data Analysis for Experimental Spectra

• Main Author: Wallace, Austin
• Format: Text
• Language: unknown
• Published: eGrove 2022
• Subjects: Quantum Chemistry; Density Functional Theory; Time Dependent Density Functional Theory; Amorphous Solids; Hartree; Carbonic acid
• Online Access: https://egrove.olemiss.edu/hon_thesis/2549; https://egrove.olemiss.edu/context/hon_thesis/article/3560/viewcontent/t.pdf

Theoretical chemistry aims to acquire wavefunctions for systems to calculate physical observables to help guide experimentation or provide rationale for particular observations. While quantum chemistry has expanded well beyond Hartree-Fock theory to produce more accurate predictions or faster computational times, this theory has formed the foundation of the field through providing a means to solve the electron-electron repulsion term as simply an average field and to acquire converged molecular orbitals through the self-consistent-field method. When attempting to describe large molecular systems that can populate many microstates, the Boltzmann distribution provides a means for determining the relative abundances of each microstate in the system at a given temperature allowing quantum chemistry predictions to be expanded to larger molecular systems to better match experiment. Through the usage of density functional theory in Chapter 4, carbonic acid clusters are explored to find the lowest in energy and the electronic structure computed to generate theoretical data to compare with experiment. In Chapters 5 and 6, amorphous clusters are generated and electronic excited states computed to construct UV spectra through combining quantum chemistry and the Boltzmann distribution to compare with experiment. Lastly, Chapter 3 is a bit different from the rest of the thesis due to being a data analysis tool for experimentalist that computes the λonset for absorption and emission spectra. Overall, this thesis primarily focuses on electronic spectroscopy through detailing the generation of spectra for specific molecular systems theoretically or processing experimental spectra to provide a standardized method for approximating the E(0-0) optical energy gap.