Photoelectron Imaging of Molecular Anions

Abstract

This dissertation employs photoelectron imaging spectroscopy to explore properties of molecular electronic structure of heterocyclic aromatics. First, photoelectron angular distributions of these molecules are modeled to gain insight into their stability and electronic structure. The model is adapted to include the local charge density of anionic aromatics and find trends in photoelectron angular distributions. Applications of this model may have the power to predict photoelectron angular distributions from ab initio calculations. Second, a photoelectron imaging study of three anion isomers of deprotonated isoxazole is presented. Deprotonation at the most acidic position yields the isoxazolide anion, but the reaction at another site cleaves the O-N bond and opens the ring of the anion. This bond breaking causes a rearrangement of the energies of its electronic states. The sensitivity of these competing deprotonation pathways is explored by adjustments made to ion generation conditions. Third, a study of bond-breaking probes a covalent bond stretched far beyond its equilibrium length. This transient structure has an inherently multiconfigurational electronic structure due to the interaction of two unpaired electrons−a diradical−over the distance of a few angstroms. This is achieved by attaching an electron to isoxazole which populates an antibonding orbital and cleaves the O-N bond. Photodetachment of this electron leave the molecule as a diradical with the molecular framework holding the two radical centers at a chemically relevant distance. Quantum calculations help to distinguish and assign the nearly degenerate electronic states in this almost bonded aromatic molecule. Ideas for future study are presented in the final chapter.