Defying Limits: Electron Interactions With Atmospheric Species

Abstract

This dissertation encompasses the idea of defying limitations or common generalizations- the abnormal methods that are needed and used in these discussed experiments. Photoelectron imaging spectroscopy is used to study the electronic properties and structures of negative ions. The following anions are studied: sulfur monoxide anion (SO–), phenide anion (Ph–), and phenide-water clusters (Ph–H2O and Ph–(H2O)2). The common assumption used is that the photoejected electron has little to no interaction with the neutral species. The observations and understanding of hydration shift and stabilizations in the photoelectron spectroscopy community reference from anions at the ground state and not for thermally excited polyatomic ensembles. Ab initio calculations become limited in this sense, such that new methods are required to fully analyze the congested experimental spectra. Microhydration interactions determines the upper bound limit temperature of stable clusters or the characteristic solvation temperature.The photoelectron angular distributions (PADs) of SO– is studied and compared through experimental and computational methods. The departing photoelectron interacts with the neutral residue of SO due to significant dipole moment, making common ab initio computational methods that are used for photoelectron anisotropy parameters limited. Different methods (point dipole-field and multi-center) were used instead to understand the exit-channel interactions of SO for the X^3 Σ^- state and a^1 ∆ state. The point dipole-field model with D > 0.6 a.u. (D = dipole moment) and the multi-center model with ZS = 0.10 – 0.15 (partial charge on the sulfur atom) were consistent with the experimental PADs data. The research on SO⁻ advances the dipole-field model by introducing detachment from a π*orbital. Analyzing the data of hot species vs. cold species require different methods that are not as straight forward, which is seen in both phenide and phenide-water clusters. Calculating using only the state-specific approach would result in millions of years to converge; therefore, statistical methods (e.g., energy conservation model) were used to analyze the congested photoelectron energy spectrum for hot phenide. The Franck-Condon (FC) factors of ground cold phenide (0 K) was used as a reference for the statistical models. The estimated experimental temperature of phenide was found to be 700 K. The temperature of phenide-water cluster was 560 K, which was determined by the characteristic solvation temperature (CST). The CST is an intrinsic property of the clusters and is determined by the microsolvation interactions and not by the electron source (e.g., electron cannon) temperature. Furthermore, experiments have been done on O2– Benzoxazole with calculations still in the process. This project will add more information on how different solvents (e.g., benzoxazole) affect the oxygen anion. This also continues the research of how the departing electron cannot be assumed as negligible. Future experiments on S2– solvated with other species will hopefully be performed to peer into the affect of changing the anion core between O2– and S2–. Lastly, hot ions will still be investigated as this is a relatively new topic in the Sanov lab.