Graduate Program

Chemistry

Degree Name

Master of Science (MS)

Semester of Degree Completion

Spring 2019

Thesis Director

Rebecca A. Peebles

Thesis Committee Member

Douglas G. Klarup

Thesis Committee Member

Daniel J. Sheeran

Thesis Committee Member

Edward M. Treadwell

Abstract

Supercritical carbon dioxide (sc-C02) is an excellent green solvent, but its properties are not thoroughly understood. For example, fluorinated compounds have higher than expected solubility in sc-C02. Microwave spectroscopy is one way to learn more about sc-C02 because it can be used to determine detailed structures of small clusters of molecules. The purpose of this investigation was to study weak hydrogen bonding interactions in complexes of fluorinated ethylene (solute) with carbon dioxide (C02, solvent). Investigations on dimers with one C02 molecule and fluorinated ethylene were carried out previously and found two different structures for vinyl fluoride (VF) ... C02, one structure for 1, l -difluoroethylene ... C02 and one structure for tritluoroethylene ... C02. In this study, the trimer VF ... C02 ... C02 has been studied using chirped-pulse Fourier-transform microwave (CP-FTMW) spectroscopy. Four structures were predicted using theoretical calculations and two of these possible structures were observed experimentally. Based on measured rotational constants, and comparing intensities with predicted dipole components, the actual structures were predicted well by theoretical calculations. Both observed trimer structures have CH ... O interactions that are similar to the observed dimers. Weakly bound tetramers were the next step in the series of complexes of C02 with fluorinated ethylene. But before going to the next step, we were able to observe 5 constant difference patterns from original scans which were not previously assigned. Then these 5 patterns were fully assigned and the experimental rotational constants for the spectra were found. But the cluster formulas and structures associated with them were unknown. Then to find the structures for these unknown molecular clusters we collected additional scans with different C02 concentrations. These data helped us to develop different analytical tools using MathCAD program for identifying the formulas for assigned spectra as well as extracting 5 more unknown molecular clusters. We were able to come up with some possible matches for the unknown clusters, ranging from trimers up to pentamers with the aid of Gaussian and ABCluster program. Future work will involve finding molecular structures for unknown cluster and finding ways to better mimic C02 salvation of VF.

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