Color center laser kinetic spectroscopy

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Title: Color center laser kinetic spectroscopy
Author: Stephens, James Wesley
Advisor: Curl, Robert F., Jr.
Degree: Doctor of Philosophy thesis
Abstract: High resolution color center laser kinetic spectroscopy has been used to study the kinetics and spectroscopy of free radicals. The radicals are produced in a flowing system by the excimer laser photolysis of stable precursors. The transient infrared absorptions of the radicals are monitored with better than 1 $\mu$s time resolution. Spectra of the ethynyl radical (C$\sb2$H), produced by photolysis of acetylene, were collected between 3000 and 3600 cm$\sp{-1}$ with a goal of identifying the CH stretching fundamental of the molecule. A number of new bands of C$\sb2$H and its carbon-13 analogue ($\sp{13}$C$\sp{13}$CH) were observed and rotationally analyzed. These bands include three C$\sb2$H bands of $\sp2\Sigma\sp+$ + $\gets$ $\sp2\Sigma\sp+$ symmetry, one C$\sb2$H band of $\sp2\Pi$ $\gets$ $\sp2\Pi$ symmetry, three $\sp{13}$C$\sb2$H bands of $\sp2\Sigma\sp+$ + $\gets$ $\sp2\Sigma\sp+$ symmetry, and one $\sp{13}$C$\sb2$H band of $\sp2\Pi$ $\gets$ $\sp2\Pi$ symmetry. A number of $\sp{13}$C analogues of $\sp{12}$C$\sb2$H bands were identified. However, no conclusive assignment has been made for the CH stretch. Two tentative assignment schemes are given for several of the bands. The kinetics of the C$\sb2$H + O$\sb2$ reaction were studied with a goal of determining the reaction products. OH radicals were determined to be a minor product of this reaction. Experiments designed to determine the relative importance of the hydrogen atom producing channel were inconclusive. In other kinetic studies, a high temperature furnace was constructed to determine the temperature dependences of the product channels of the NH$\sb2$ + NO reaction. The reaction was initiated by the photolysis of NH$\sb3$ in the presence of NO. The branching ratios of the OH and H$\sb2$O producing channels were determined at 26, 400, 700, and 925$\sp\circ$C by comparison of the increase in OH and H$\sb2$O absorption signals with the decrease in an NH$\sb3$ absorption signal. Branching ratios were calculated from the raw signals by using the infrared cross sections of the molecules, measured in separate experiments. The branching ratio of the OH channel is 14% at room temperature and increases to 25% at 925$\sp\circ$C. The total of the two channels (OH plus H$\sb2$O) accounts for 100% of the reaction at room temperature; however, this number drops to about 80% for higher temperatures, possibly indicating the onset of another channel.
Citation: Stephens, James Wesley. (1989) "Color center laser kinetic spectroscopy." Doctoral Thesis, Rice University.
Date: 1989

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