Infrared Studies of Intramolecular Rovibrational Relaxation (Kinetics, Energy Transfer)
Kulp, Thomas Jan
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https://hdl.handle.net/2142/70349
Description
Title
Infrared Studies of Intramolecular Rovibrational Relaxation (Kinetics, Energy Transfer)
Author(s)
Kulp, Thomas Jan
Issue Date
1986
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Physical
Abstract
Infrared fluorescence data is presented which demonstrates the extent of intramolecular vibrational relaxation from the CH stretching modes of several organic molecules. The molecules are isolated and cooled in a pulsed supersonic expansion. The infrared fluorescence is collected and dispersed using either a cryogenic Michelson interferometer or a circularly variable filter wheel. Resolved fluorescence spectra from dimethyl ether and 1,4 dioxane indicate that the energy distribution within each molecule is dependent upon the CH stretch that is excited. The fluctuations in the relaxed mode energy content with excitation energy can be fit by a statistical model which assumes coupling to all rovibrational states of the correct symmetry within 1 cm('-1) of the excitation frequency. The comparison of the relaxation in beams with rotational temperatures of 2 and 20 K demonstrates the extent of the rotational dependence of the IVR. It is shown that the level of rotational excitation affects both the extent and destination of the vibrational energy flow. Fluorescence spectra from the molecules 1,3 dioxolane and tetrahydropyran are also shown. The fact that each is structurally similar to 1,4 dioxane is used as a basis for comparison of the IVR in each case. It is shown that the presence of the pseudorotor in the five membered ring 1,3 dioxolane enhances the state density such that it is similar to that of the other two molecules. The relaxation in dioxolane and tetrahydropyran is shown to be less state selective than that of dioxane. It is demonstrated that the relaxation in methyl formate can also be fit. Using the laser at higher resolution (.18 cm('-1)), it was possible to take fluorescence excitation spectra which allowed lower limits to be set on the rovibrational lifetimes of some states. In all cases, the linewidths observed were limited by the width of the laser. Lower limits of 15 psec were set on the lifetimes of low (1-2) J states of dimethyl ether and methyl formate, and high (8-12) J states of methyl formate and 1,4 dioxane. Finally, band contour dependences of the dilution factor are presented for three methyl formate CH stretches and one in dimethyl ether. (Abstract shortened with permission of author.)
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