Inquiring photoelectrons about the dynamics in liquid water
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Beschreibung
This thesis reports two main topics of liquid water in conjunction with liquid-microjet photoelectron spectroscopy. The first topic is concerned with the electronic-structure interactions in liquid water upon oxygen 1s core-level ionization with tunable soft X-rays. The main question here is how a core-ionized water molecule relaxes when interacting with its hydrogen-bonded neighbors in liquid water. The answer is found in the autoionization spectra from light and heavy liquid water, which exhibits a high-energy contribution next to the normal Auger-electron peaks. This feature is absent in the respective gas-phase spectra, i.e., originating from states which must arise from autoionization process involving interaction with the neighboring water molecules. Two novel processes are considered; both are assisted by the ultrafast proton transfer from the ionized water to a neighboring water molecule, but they differ by the autoionization mechanism of the evolving transient cationic water complex. One resembles intermolecular Coulombic decay (ICD), an efficient energy transfer mechanism ionizing neighboring molecules, and the other is a local Auger-decay of the excited OH radical. In either case, reactive charge-delocalized dicationic complexes are formed, which play an important role for subsequent chemical reactions. The second large topic of the thesis discusses how far (photo)electrons travel in water, and how the many elastic scattering events affect their detected angular distribution. This information is crucial for describing, for instance, electron collision processes in radiation-chemistry context. However, in the light of the present photoelectron spectroscopy study, the more pressing question is how deep the technique probes into solution. Here, the relative effects of elastic and inelastic scattering lengths at and below the liquid water surface are determined. This is based on a measurement of the angular distribution of the oxygen 1s photoelectron signal over a large range of photon (soft X-ray) energies, from which values of the anisotropy parameter can be determined. Future directions and challenges of this still young and exciting field of research of liquid water and aqueous solution – be it in chemical, biological, or physical context – will be addressed.
This thesis reports two main topics of liquid water in conjunction with liquid-microjet photoelectron spectroscopy. The first topic is concerned with the electronic-structure interactions in liquid water upon oxygen 1s core-level ionization with tunable soft X-rays. The main question here is how a core-ionized water molecule relaxes when interacting with its hydrogen-bonded neighbors in liquid water. The answer is found in the autoionization spectra from light and heavy liquid water, which exhibits a high-energy contribution next to the normal Auger-electron peaks. This feature is absent in the respective gas-phase spectra, i.e., originating from states which must arise from autoionization process involving interaction with the neighboring water molecules. Two novel processes are considered; both are assisted by the ultrafast proton transfer from the ionized water to a neighboring water molecule, but they differ by the autoionization mechanism of the evolving transient cationic water complex. One resembles intermolecular Coulombic decay (ICD), an efficient energy transfer mechanism ionizing neighboring molecules, and the other is a local Auger-decay of the excited OH radical. In either case, reactive charge-delocalized dicationic complexes are formed, which play an important role for subsequent chemical reactions. The second large topic of the thesis discusses how far (photo)electrons travel in water, and how the many elastic scattering events affect their detected angular distribution. This information is crucial for describing, for instance, electron collision processes in radiation-chemistry context. However, in the light of the present photoelectron spectroscopy study, the more pressing question is how deep the technique probes into solution. Here, the relative effects of elastic and inelastic scattering lengths at and below the liquid water surface are determined. This is based on a measurement of the angular distribution of the oxygen 1s photoelectron signal over a large range of photon (soft X-ray) energies, from which values of the anisotropy parameter can be determined. Future directions and challenges of this still young and exciting field of research of liquid water and aqueous solution – be it in chemical, biological, or physical context – will be addressed.
Autor*in
Stephan Thürmer
Themen in »Inquiring photoelectrons about the dynamics in liquid water«
BESSY II Helmholtz-Zentrum Berlin aqueous solutions liquid water liquid-jet photoemission spectroscopy