Date of Award

Spring 1-1-2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

First Advisor

J. Mathias Weber

Second Advisor

Veronica M. Bierbaum

Third Advisor

W. Carl Lineberger

Fourth Advisor

G. Barney Ellison

Fifth Advisor

Heather Lewandowski

Abstract

This thesis describes research on the electronic properties of nitroalkane anions, CH3(CH2)nNO2 (where n=0,1,2, and 3), using a newly built velocity-map imaging photoelectron spectrometer. The nitroalkanes are an intriguing class of molecules that possess many similarities owing to the dominating presence of the nitro group. They all possess relatively low adiabatic electron affinities, large dipole moments, and undergo similar distortions (largely localized within the nitro group) upon electron attachment. The focus of the studies presented in this thesis is quantitatively characterizing the anion and neutral states, determining fundamental molecular properties (i.e., adiabatic electron affinities, bond dissociation energies, vertical detachment energies, etc.), and highlighting some of the interesting dynamics that the nitroalkane anions can exhibit using photoelectron spectroscopy.

The first two studies present the photoelectron spectra of nitromethane and nitroethane anions. As these molecules are small enough to be tractable by a more involved theoretical analysis, ab initio theory and Franck-Condon simulations were utilized to simulate and interpret the photoelectron spectra. In order for the simulations to achieve good agreement with the experimental spectra, additional efforts were directed at characterizing the torsional potentials of the methyl and ethyl groups and predicting the contribution of torsional motion to the photoelectron spectra. These investigations led to new assignments for the adiabatic electron affinities, the first observation of their dipole-bound states in photoelectron spectra, and determinations of the C-NO2 bond dissociation energies for the nitromethane and nitroethane anion.

The third study presents the photoelectron spectra of nitropropane and nitrobutane anions. Each of these molecules possesses a number of stable anion and neutral conformers. Ab initio theory and Franck-Condon simulations were employed to identify possible conformations responsible for the dominant features in the photoelectron spectra. Finally, an anomalous feature belonging to a separate photoelectron emission pathway was identified in the photoelectron spectrum using spectra obtained at different photon energies and through an analysis of the angular distributions.

The nitroalkane anions possess adiabatic electron affinities that are smaller than the transition energies of their fundamental CH stretching modes. As a consequence, excitation of one of these modes will lead to vibrational autodetachment that is facilitated by intramolecular vibrational excitation. The last study presents vibrational autodetachment photoelectron spectra of the nitromethane anion. The spectra were analyzed using several simple models to extract some of the important underlying information regarding the intramolecular vibrational relaxation occurring prior to vibrational autodetachment.

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