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Disputation Karen Denise Mudryk

16.08.2021 | 15:00
Thema der Dissertation:
Electronic-structure insights into aqueous redox chemistry: permanganate and manganate ions studied using liquid jet photoelectron spectroscopy
Abstract: This dissertation presents a combined study of the electronic structure and redox properties of permanganate (MnO4−) and manganate (MnO42-) ions in aqueous solution using liquid jet soft X-ray photoelectron spectroscopy (XPS). MnO4−(aq.) is a versatile, strong oxidizing agent and redox precursor of manganese species with different oxidation states.
MnO42-(aq.) is a transient species that forms a highly-reversible redox pair with MnO4−(aq.). Such redox properties make these complexes attractive for sustainable (electro-)chemical applications. Sample sources – a micro-mixing scheme and an electrolysis cell liquid jet – were developed to generate MnO42 (aq.) transient ions. Binding energy-scaled molecular orbital diagrams were produced from MnO4−(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 and hybridization of and electronic coupling between the valence electrons. 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. The results were applied to infer thermodynamic parameters of half redox reactions involving the MnO4−(aq.) / MnO4•(aq.) and MnO42- (aq.) / MnO4−(aq.) redox pairs, including oxidative reorganization energies (ox), adiabatic ionization energies / Gibbs free energy of oxidation (ΔGox) and vertical electron affinities. The work demonstrates 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 methods.

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16.08.2021 | 15:00