Date of Award
Ph.D. in Chemistry
Gregory S. Tschumper
Steven R. Davis
Nathan I. Hammer
University of Mississippi
High-accuracy electronic structure theory methods are important in the field of chemistry for probing molecular properties of chemically relevant systems that are often difficult to obtain experimentally. This work focuses primarily on using robust computational techniques to characterize not only small triatomic anions but also anion-water clusters in addition to investigating their vibrational frequencies near the complete basis set (CBS) limit. The MP2 and CCSD(T) ab initio methods are used with second-order vibrational perturbation theory (VPT2) and vibrational configuration interaction (VCI) theory in this work to compute the fundamental vibrational frequencies of small anions. Due it being arduous to experimental isolate these anions in the gas-phase and observe their vibrational spectra, their computed anharmonic frequencies provide important reference values that can help quantify spectroscopic perturbations induced by solvents or counter-ions. Comparisons are made between anions containing pnictogen and chalcogen elements (e.g., nitrogen and oxygen) as well as their heavier analogs (e.g., phosphorus and sulfur) as well as to available experimental data. The N-body:Many-body QM:QM technique as well as MP2 and density functional theory methods are benchmarked against the CCSD(T) method, often considered the gold standard, for the examination of small hydrogen-bonded clusters.
Barlow, Kayleigh R., "Computational Investigation of the Structures and Vibrational Spectra of Isolated and Hydrated Ions" (2023). Electronic Theses and Dissertations. 2480.
Available for download on Saturday, September 13, 2025