Date of Degree

2013

Document Type

Dissertation

Degree Name

Ph.D.

Program

Chemistry

Advisor

Cherice M. Evans

Committee Members

Gary L. Findley

Lawrence W. Johnson

Jianbo Liu

Subject Categories

Chemistry

Abstract

The ability to predict accurately the energy V0(ρ) of the quasi-free electron along the entire density (ρ) range of a supercritical fluid has applications in determining the ideal thermodynamic conditions for chemical reactions involving charged species. The previously established field ionization method of extracting V0(ρ) from the fluid density dependent shift Δ(ρ) in the ionization energy of a dopant molecule has led to the discovery of a novel effect on V0(ρ) occurring near the critical isotherm of the fluid. Unfortunately this method has limitations in determining V0(ρ) in fluids with low critical temperatures as well as fluids opaque to vacuum ultraviolet radiation. Thus, accurate determination of V0(ρ) in repulsive fluids (i.e., those possessing a positive zero kinetic energy electron scattering length) using field ionization is difficult.

The new method developed in this study, namely field enhanced photoemission, allows for the direct determination of the quasi-free electron energy from the density dependent shift in the work function of a metal electrode submerged in the fluid. This mitigates the problems posed by field ionization while producing results with similar precision. Field enhanced photoemission was verified by measuring V0(ρ) of Ar, an attractive fluid (i.e., one with a negative zero kinetic energy electron scattering length) studied extensively in the past by field ionization, before applying the method to the study of V0(ρ) in the repulsive fluids Ne, He and N2. The new results showed a distinct critical point effect on V0(ρ), which was accurately modeled with the local Wigner-Seitz approach developed for attractive fluids. Thus, this work extends our theoretical model to repulsive fluids.

Unlike the attractive fluids studied in the past, the quasi-free electron energy in the repulsive fluids presented here is strictly positive. A careful analysis of the terms contributing to V0(ρ) within the local Wigner-Seitz model leads one to expect the quasi-free electron energy to be positive in repulsive fluids in general. A discussion of fluid density dependent behavior of the kinetic and potential energy terms contributing to V0(ρ) is presented along with an explanation of the evolution of the shape of the V0(ρ) curves for the fluids studied.

Included in

Chemistry Commons

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