Electronic structure insights into aqueous redox chemistry permanganate and manganate ions studied using liquid jet photoelectron spectroscopy

This thesis presents a combined study of the microscopic electronic structure and macroscopic redox properties of permanganate MnO4 amp; 8722; and manganate MnO42 ions in aqueous solution using liquid jet soft X ray photoelectron spectroscopy XPS . MnO4 amp; 8722; aq. is a versatile, strong oxidizing agent and redox precursor of manganese species with a range of oxidation states. MnO42 aq. is a transient species that acts both as an oxidizing or reducing agent, forming a highly reversible redox pair with MnO4 amp; 8722; aq. in alkaline environments. Such redox properties make these transition metal complexes TMCs attractive for sustainable electro chemical applications. The goal of this work was to gain insight into the absolute energetics and redox behavior of MnO4 amp; 8722; aq. and MnO42 aq. from electronic structure information. Alternative sample sources a micro mixing scheme and an electrolysis cell liquid jet were developed to generate and study MnO42 aq. transient ions. Within a single configuration and single active electron electronic structure picture, binding energy scaled molecular orbital MO diagrams were produced from MnO4 amp; 8722; aq. and MnO42 aq. XPS data. Mn 2p and O 1s resonantly enhanced photoelectron spectroscopy RPES measurements revealed intramolecular Auger processes and valence electron binding energies that were not accessible from the XPS experiments, as well as hybridization of and electronic coupling between the valence electrons. In addition, the O 1s RPES experiments revealed intermolecular coulombic decay ICD processes, signatures of electronic coupling between solute and solvent molecules in the first solvation shell. For MnO4 amp; 8722; aq. at 0.2 M concentration, similar electronic energetics were observed at the gas solution interface and in the solution bulk, independently of the nature of the counter ion Na aq. or K aq. . Depth profiling experiments at 0.2 M and 1.0 M concentration highlighted a tendency of MnO4 amp; 8722; aq. to accumulate in the solution bulk and away from the interface, with non linear accumulation behavior occurring for the higher concentration. Through comparison to the gas phase ionization energetics, the Gibbs free energy of hydration amp; 916;Ghyd for isolated MnO4 amp; 8722; was also calculated. For MnO42 aq. , valence band features could only be isolated in surface sensitive XPS experiments and RPES experiments were relied on to study bulk solution energetics. These results were applied to infer thermodynamic parameters of half redox reactions involving the MnO4 amp; 8722; aq. MnO4 aq. and MnO42 aq. MnO4 amp; 8722; aq. redox pairs, including oxidative reorganization energies, adiabatic ionization energies Gibbs free energy of oxidation amp; 916;Gox and vertical electron affinities. For the MnO42 aq. MnO4 amp; 8722; aq. redox pair, the amp; 916;Gox value purely extracted from spectroscopic data was shown to match the reported electrochemical value. Overall, the extracted redox parameters demonstrate how insights into the macroscopic redox properties of chemical systems can be built up from microscopically molecularly sensitive measurements. The methodology can be extended to aqueous redox active species that cannot be probed by conventional electrochemical method