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Electronic decay cascades in media initiated by resonant absorption of X-Ray photons

Miteva, Tsveta

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Abstract

The resonant-Auger -- interatomic Coulombic decay (RA-ICD) cascade was recently proposed as a very efficient means of controlling the generation site and energies of slow ICD electrons. The control mechanism was verified in a series of experiments where both the energy of the photons producing the initial core excitation, and the neighbouring species were varied. The aim of this thesis is to provide a detailed theoretical investigation of the RA-ICD cascade in rare-gas dimers and give a first insight into the course of the cascade in aqueous medium.

The potential energy curves (PECs) of ionisation satellites are key ingredients in the theoretical description of electronic decay cascades. In the first chapter, we conducted a study on the PECs of the ionisation satellites of the ArHe dimer with a view to modelling such PECs in heavier dimers. Our results show that the complex valence structure in the rare-gas atom leads to the mixing of different electronic configurations of the dimer, which prevents one from assigning a single dicationic parent state to some of the ionisation satellites.

In the second part of the thesis, we present and analyse the ICD-electron and kinetic-energy-release (KER) spectra following different resonant core excitations of Ar in the rare-gas dimers Ar$_2$ and ArKr. We demonstrate that the manifold of ICD states populated in the resonant Auger process consists of fast- and slow-decaying ionisation satellites, and that the accurate description of nuclear dynamics in the latter ICD states is crucial for obtaining theoretical electron and KER spectra in good agreement with the experiment. We also show that by varying the neighbouring atom one can tune the energies of the emitted ICD electrons and even control the ICD yield.

Finally, as a first step towards the investigation of the RA-ICD cascade in aqueous medium, we present and discuss the X-Ray absorption spectra of microsolvated clusters of Na$^{+}$ and Mg$^{2+}$ at the metal 1s threshold. In this case it is important to investigate the nature of the core-excited states prior to studying the RA-ICD cascade, since in a solution the excited electron is delocalised and may ionise within the lifetime of the core hole, thus changing the course of the cascade. Our findings show that for a complete first solvation shell, the excited electron becomes spatially extended towards the water molecules.

Item Type: Dissertation
Supervisor: Cederbaum, Prof. D. Lorenz S.
Date of thesis defense: 16 July 2015
Date Deposited: 31 Jul 2015 08:33
Date: 2015
Faculties / Institutes: Fakultät für Chemie und Geowissenschaften > Institute of Physical Chemistry
Subjects: 000 Generalities, Science
500 Natural sciences and mathematics
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