Experimentelle Erforschung der elektronischen Struktur und der ultraschnellen Elektronendynamik von Übergangsmetallkomplexen in Wasser mittels zeitaufgelöster Zwei-Farben Pump-Probe Photoelektronen-Spektroskopie
Zusammenfassung der Projektergebnisse
The major conclusions can be summarized as follows: 1. For the dihydrogen phosphate H2PO4-, the binding energy of the HOMO electron increases from 5.06 eV in the gas phase25 to 9.5 eV. Hydrogen phosphate (HPO42-) and phosphate (PO43-) anions have never been isolated in the gas phase, due to their electronic instability, but the binding energies in water were measured to be 8.9 eV for HPO42- and 8.4 eV for PO43-. Liquid microjet photoelectron spectroscopy thus characterizes the electronic stabilization of the anion by the solvent. See Figure 5. 2. Based on our theoretical calculations, we estimate that about 16 water molecules are needed to support the electronic stability of PO43- while 2-3 water should suffice to support the existence of HPO42-. 3. It was possible to reproduce the experimentally reported binding energies (and photoelectron spectra) within the hybrid cluster/continuum approach. However, for multiply charged anions it was necessary to fully solvate the phosphate anion with two layers of explicit water molecules to reproduce the experiment. 4. Our calculations show that the protonation (i.e. formation of covalent bond between H+ and the anion) increases the VIE of phosphate anion, while ion pairing with Na+ does not influence it due to the screening effect of water. This conclusion is in a full agreement with the experiments for phosphates in different protonation states studied at different electrolyte concentrations. 5. Both experimental and simulated photoelectron spectra exhibit a rather broad peak width (above 1 eV), which can be rationalized as a combination of distribution of solvent and counterion structures, as well as vibrational and electronic states of the anion. For the former (inhomogeneous) broadening the current calculations show that the distribution of solvent structures gives the major contribution.
Projektbezogene Publikationen (Auswahl)
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Transforming anion instability into stability: Contrasting photoionization of three protonation forms of the phosphate ion upon moving into water; J. Phys. Chem. B (2012), 116, 13254−13264
Eva Pluhařová, Milan Ončák, Robert Seidel, Christi Schroeder, William Schroeder, Bernd Winter, Stephen E. Bradforth, Pavel Jungwirth, and Petr Slavíček
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Photoelectron Angular Distributions from Liquid Water: Effects of Electron Scattering; Phys. Rev. Lett. (2013), 111, 173005
Stephan Thürmer, Robert Seidel, Manfred Faubel, Wolfgang Eberhardt, John C. Hemminger, Stephen E. Bradforth, and Bernd Winter
