Structure and Dynamics of Small Molecules and Anions: Negative-ion photoelectron spectroscopy

Miller, Elisa M.

Graduate Thesis Or Dissertation

Structure and Dynamics of Small Molecules and Anions: Negative-ion photoelectron spectroscopy Public Deposited

Analytics

Citations

Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/n583xv088

Abstract

Photoelectron spectroscopy of gas-phase anions is utilized to study the spectroscopic and dynamic properties of anions and anionic clusters. The photoelectron spectrum of IBr⁻(X̃²Σ⁺) leads to more accurate measurements of a number of molecular properties, such as the electron affinity of IBr (EA(IBr) = 2.512±0.003 eV), equilibrium geometry of the anion ground state (R_e(I–Br^⁻) = 3.01±0.01 Å), and dissociation energy of the anion ground state (D₀(I–Br^-) = 0.966±0.003 eV). The photoelectron spectrum of IBr^-(CO₂)_n, n = 1 – 3, demonstrates minimal perturbation to the IBr^- electronic structure, and the EAs for solvated IBr(CO₂)_n, n = 1 – 3, are determined. The presence of the CO₂ influences the dissociation dynamics along two excited states of IBr^- by enabling nonadiabatic transitions. Time-resolved photoelectron spectra of IBr^- and IBr^-(CO₂) are taken to measure these dissociation dynamics, which when combined with theory leads to a mechanism. The solvation energy of CO₂ and the ability of CO₂ to temporarily acquire partial charge as it bends facilitate the charge transfer in the two photoexcitation/photodissociation channels studied.

Photoelectron spectroscopy of ICN^- (X̃²Σ⁺) probes transitions to the ground state and first five excited states of neutral ICN. The first three excited states and a conical intersection region between the ³Π₀₊ and ¹Π₁ states are spectroscopically resolved. Through thermochemical cycles involving narrow transitions to excited states, the EA(ICN) is found to be 1.34(+.04/-.02) eV and the D₀(ICN^-) equals 0.83(+.04/-.02) eV. In addition, four spectral peaks are observed with photoelectron kinetic energies of ~0, ~45, ~70, and ~150 – 200 meV, and the kinetic energy is unchanged as the photodetachment photon energy is varied from 2.5 to 4.2 eV. These autodetachment features are a result of photoexcited ICN^- converting internal energy into CN rotation followed by a quasi-thermionic emission of electrons to produce neutral ICN/INC in its ground electronic state. The autodetachment features persist when ICN^- is solvated by Ar or CO₂, indicating that solvation does not modify the autodetachment mechanism. In addition to these investigations, current projects are in progress, such as HO₃^-, that require abundant Ar cooling and an entrainment block as part of the anion source.

Creator