Vibrational spectroscopy in cryogenic solutions: application of thermal lensing and Fourier transform techniques to the study of molecular C-H overtone transitions.
This dissertation explores the application of thermal lensing to vibrational overtone spectroscopy in cryosolutions. Specifically, C-H (delta v = 6) overtone spectra of hydrocarbons dissolved in liquefied rare gases are presented. In addition, Fourier transform (IR, NIR, VIS) spectra between 5000 and 15000 cm-1 are provided for each sample. Main contents were organized in five chapters. First, an introduction on the thermal lens effect, covering principles, theoretical modeling, and general applications. Second, delineation of experimental procedures and instrumental setups. Third, a thorough analysis of thermal lens intensities in methane-argon and methane-nitrogen solutions. Particular topics include concentration and solvent dependency, detection limits, and time-profiles in single and dual-beam experiments. Fourth, description of overtone spectra of saturated hydrocarbons (ethane, propane, butane, isobutane) and calculation of local-mode parameters. And fifth, a similar analysis as before for alkene (ethylene, propylene, isobutylene, cis-2-butene, trans-2-butene) solutions. The main conclusion of the project is the successful applicability of thermal lensing to cryogenic samples, showing comparable performance to room-temperature studies.