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Abstract
Modern quantum mechanical theories, including high-level ab initio methods and density functional theory, have been applied to a variety of molecular systems. The first work performs a comprehensive anharmonic vibrational analysis of propargyl radical. A highly-accurate quartic force field was constructed with coupled-cluster including singles and doubles and perturbatively applied triple excitations [CCSD(T)] using the aug-cc-pVTZ basis set, complemented with a quadratic force field extrapolated to the complete basis set limit using cc-pVXZ (X=T, Q, 5) basis sets. Fundamental vibrational frequencies were computed with the complete quartic force field based on vibrational perturbation theory. In the second work, accurate electron affinities and ionization potentials of trans- and cis-hydroxyformyl radicals were determined via systematic ab initio investigations. State-of-the-art ab initio electronic structure theories combined with aug-cc-p(C)VXZ (X=2-6) basis sets were utilized to extrapolate to the complete basis set full configuration interaction limit via the focal point analysis method. Core-correlation effects, special relativity, zero-point vibrational energy, and diagonal Born-Oppenheimer corrections were explicitly incorporated in the results to -1provide accuracy to the level of 0.1 kcal mol. The last work examines optimal structures, energetics, and harmonic vibrational frequencies of adamantane and a variety of its derivatives using four different density functional methods and the DZP++ basis set. Electronic affinities, ionization potentials and other properties have been predicted.