Ultraviolet photochemistry of gas phase diacetylene and infrared spectroscopy of jet-cooled tropolone derivatives and their complexes with water

Rex Kenneth Frost, Purdue University

Abstract

My thesis research is comprised of two areas. In one project, reactions of the diacetylene triplet metastable state $\rm (C\sb4H\sb2\sp*)$ with acetylene, ethene, propene, and propyne were studied in a reaction channel attached to a pulsed nozzle. The photoexcitation laser counterpropagates the molecular expansion traversing the reaction channel. Upon exiting the reaction channel, primary products are time-of-flight mass analyzed. Primary products are assigned with action spectra, photoexcitation laser power studies and reaction time studies. Relative rate constants are extracted from concentration studies. Isotopic labeling studies are used to develop reaction mechanisms. In the second project, ground state infrared spectra of jet-cooled tropolone, tropolone deuterated only in the hydroxy position, the tropolone:water 1:1 complex and 5-hydroxytropolone were recorded using a fluorescence depletion method. All C-H and O-H stretch bands of these systems are assigned. Larger red shifts but smaller intensity gains are observed for intramolecularly H-bonded O-H stretch bands compared to intermolecularly H-bonded O-H bands. The tropolone OH(v = 1) level tunneling splitting is tentatively determined to be 12 cm$\sp{-1}$. The tropolone:water 1:1 complex is tentatively proposed to be a structure where the water binds in an "exterior" site to the keto oxygen. In both tropolone:water and 5-hydroxytropolone, the structure of the intramolecularly and intermolecularly H-bonded O-H stretch bands is ascribed to vibrational state mixing with a very select subset of dark states. The observed structure appears to be dominated by 2:1 Fermi resonant mixing involving modes closely associated with the intramolecular proton tunneling coordinate. No mixing of syn and anti levels is observed in the excited vibrational states of 5-hydroxytropolone. The small OH(v = 1) level tunneling splitting in tropolone and the apparently weak mixing of syn and anti states in 5-hydroxytropolone indicate that the intramolecularly H-bonded O-H stretch mode is not closely associated with the proton tunneling reaction coordinate.

Degree

Ph.D.

Advisors

Zwier, Purdue University.

Subject Area

Chemistry

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