Date of Award

August 2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Advisor(s)

Timothy M. Korter

Keywords

Low-Frequency, Polymorphs, Raman, Solid-State Denisty Functional Theory, Terahertz, X-ray Crystallography

Subject Categories

Physical Sciences and Mathematics

Abstract

The effect of temperature plays a large role in the behavior of many physical systems. While it is certainly the case that many effects of temperature can be observed macroscopically, they are often of molecular origin, and determining why these effects occur can provide insight into the nature of chemical systems as a whole. A large portion of this work is dedicated to analyzing polymorphic forms and small organic molecules with interesting thermal effects. Low-frequency spectroscopy is a very useful tool in the investigation of polymorphs, providing a method of probing a sample to investigate the possible motions and characteristics that these systems exhibit with the effect of heating or cooling. In this work, low-frequency spectroscopy is combined with X-ray diffraction to differentiate polymorphs and analyze systems that behave anharmonically with temperature. This experimental work is complemented with solid-state density functional theory calculations, enabling for the evaluation of the energetics of the studied systems, providing insight into the relative stabilities of the studied systems over a range of temperatures, and can even elucidate the mechanisms by which polymorphic transformations may occur. Overall, this is an achievement in the understanding of thermal effects in crystalline systems made possible by the combination of experimental and theoretical techniques.

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Open Access

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