Laser-induced chemistry: A. Infrared laser probing of reactions products. B. Laser-assisted deposition of thin films
Date of Award
Dissertation - Restricted
Doctor of Philosophy (PhD)
Donaldson, William A.
Laser-induced reaction studies are powerful tools for investigating the fundamental aspects of reaction mechanisms. In addition, laser-induced chemistry can be used in interesting practical applications, such as production of gas sensor materials. Part A of this work focuses on the use of infrared laser chemistry of two reaction systems initiated photolytically. One is the OH hydrogen abstraction reaction from selected hydrocarbons and the second is the photolysis of N-thionyl-aniline. Fundamental information is provided as a result of our investigations. Part B. of the present work was focused on the development of doped SnO$\sb2$ thin-film sensors via laser-assisted Deposition. The principal precursor used in the SnO$\sb2$ thin-film deposition was Di-n-butyl tin diacetate (DBTDA).
A. The abstraction of hydrogen atoms by OH from volatile alkanes is the first step in the photochemical smog formation. A large volume of theoretical and experimental work has been done to develop kinetic information used in atmospheric modeling, but less information is available concerning the dynamics of this process. Experimental investigations of the OH hydrogen abstractions and ketenimine formation were made using time-resolved IR diode-laser gain/absorption spectroscopy. In this technique, the IR wavelength is tuned to a rovibrational transition and the change in relative population of the two states involved in transition is monitored by the change in the intensity of the IR light. A powerful tool in supporting the OH reaction experimental results was the kinetic modeling.
In the second system is probed the presence of ketenimine in the photolysis of N-thionyl-aniline. The photolysis of N-thionyl-aniline was investigated via flash-photolysis with uncertain evidence of the ketenimine intermediate.
B. DBTDA has been used previously for SnO$\sb2$ thin-film deposition via chemical vapor deposition and laser-assisted deposition of SnO$\sb2$ thin-films was reported recently in the literature using SnCl$\sb4$ as a precursor. In order to understand the DBTDA photolysis process, multiphoton-induced emission spectroscopy was used to identify photoproducts. The focused UV beam is absorbed by the DBTDA molecule generating different fragments. The presence of the CH radical between the fragments was probed via fluorescence spectroscopy. Sn-containing fragments adsorb on the support surface creating a SnO$\sb2$ thin-film. Doped films are generated using a variety of precursors such as chromium hexacarbonyl and copper acetate. Films are characterized via optical absorbance and electrical resistance measurement.