Studies of solvent-solute interactions using pressure-induced vibrational frequency shifts
Abstract
This research focuses on the measurement and modeling of vibrational frequency changes a molecule undergoes as it is solvated, as these changes are a direct consequence of the mean forces exerted on the vibrating molecule by the surrounding solvent. Theoretical modeling of intermolecular forces, and their effects on molecular vibrations are used to test our understanding and use of molecular and liquid theories to model real fluids. This work uses a perturbed hard fluid (PHF) model to predict experimental frequency shifts. The PHF model, which separates the experimental shift into repulsive and attractive parts, uses a reference hard sphere fluid to calculate mean repulsive forces, and experimental frequency data to determine a single, mean field, attractive parameter used to describe the attractive part of the frequency shift. A large portion of this research focuses on the frequency shifts of simple diatomic molecules (N$\sb2$ and HCl), but applications to polyatomic molecules are illustrated with dichloromethane. An alternative, breathing sphere model, is also proposed in order to better describe solvent effects on polyatomic normal modes. Additionally, Fermi resonance effects on polyatomic C-H stretching vibrations are analyzed using existing pressure measurements, and the effects of Fermi resonance on pressure induced solvent shifts are discussed. Finally, measurements of vibrational overtones using sensitive thermal lens absorption techniques are presented. A description of the thermal lens absorption instrument and preliminary measurements of the 4$\nu\sb1 + \nu\sb9$ overtone-combination band of dichloromethane are discussed.
Degree
Ph.D.
Advisors
Ben-Amotz, Purdue University.
Subject Area
Chemistry
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