Graduate Thesis Or Dissertation
Velocity-Map Imaging Photoelectron Spectroscopy of Small Molecular Anions Public Deposited
Gas phase anion photoelectron spectroscopy presents an opportunity for investigating molecules that are inaccessible by other experimental techniques, by providing data on the structure, reactivity and energetics of short-lived radicals and transition state species. Our recent development of a novel, plasma entrainment source of cold, weakly-bound anions opens a door to new exotic species to be investigated. In this thesis, I explore the capabilities of photoelectron spectroscopy and its application to small exotic molecular anions, while further developing and employing the novel dual-valve ion source.
The thesis begins with a brief history of photoelectron spectroscopy, followed by a description of the experimental apparatus. The first anion studied using the new anion source is the weakly bound methide anion (CH3-). This experiment provides the first measurement of the inversion splitting of this simple pyramidal carbanion. The precise measurement of the electron affinity (EA) of the methyl radical provides accurate measurements of the gas phase acidity of methane, which defines the acidity scale of hydrocarbons.
I then explore the spectroscopy of the atmospherically significant HONO molecule, via photoelectron spectroscopy of the open-shelled HONO- radical anion. HONO- is produced in a reaction between OH- and NO, a feat accomplished in the cold, collision-rich environment of the novel anion source. This experiment allows for the first measurement of the EA of HONO and the excitation energy to its lowest excited state, the triplet, which is inaccessible by most spectroscopic techniques.
Next, I investigate of the electronic structure of singly substituted alkoxy radicals. The new dual-valve source allowed for controlled synthesis of hydroxymethoxide and aminomethoxide. The selective substitution allows us to probe what effect the substituting group has on the electronic structure of alkoxy radicals, leading to a correlation between the substituent group’s electronegativity and the EAs and excited state energies of the radicals.
Finally, I investigate the biologically relevant 7-azaindole and its hydrogen bonded dimer. The photoelectron spectrum of 7-azaindolide provides a measurement of the EA of the 7-azaindolyl radical and reveals an unexpected behavior of the spectrum, where most of the observed signal derives from a process other than direct photodetachment.
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