| 1. |
- Miteva, Tsveta, et al.
(author)
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The All-Seeing Eye of Resonant Auger Electron Spectroscopy : A Study on Aqueous Solution Using Tender X-rays
- 2018
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In: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 9:15, s. 4457-4462
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Journal article (peer-reviewed)abstract
- X-ray absorption and Auger electron spectroscopies are demonstrated to be powerful tools to unravel the electronic structure of solvated ions. In this work for the first time, we use a combination of these methods in the tender X-ray regime. This allowed us to address electronic transitions from deep core levels, to probe environmental effects, specifically in the bulk of the solution since the created energetic Auger electrons possess large mean free paths, and moreover, to obtain dynamical information about the ultrafast delocalization of the core-excited electron. In the considered exemplary aqueous KCl solution, the solvated isoelectronic K+ and Cl- ions exhibit notably different Auger electron spectra as a function of the photon energy. Differences appear due to dipole-forbidden transitions in aqueous K+ whose occurrence, according to the performed ab initio calculations, becomes possible only in the presence of solvent water molecules.
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| 2. |
- Richter, Clemens, et al.
(author)
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Competition between proton transfer and intermolecular Coulombic decay in water
- 2018
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In: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 9
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Journal article (peer-reviewed)abstract
- Intermolecular Coulombic decay (ICD) is a ubiquitous relaxation channel of electronically excited states in weakly bound systems, ranging from dimers to liquids. As it is driven by electron correlation, it was assumed that it will dominate over more established energy loss mechanisms, for example fluorescence. Here, we use electron-electron coincidence spectroscopy to determine the efficiency of the ICD process after 2a(1) ionization in water clusters. We show that this efficiency is surprisingly low for small water clusters and that it gradually increases to 40-50% for clusters with hundreds of water units. Ab initio molecular dynamics simulations reveal that proton transfer between neighboring water molecules proceeds on the same timescale as ICD and leads to a configuration in which the ICD channel is closed. This conclusion is further supported by experimental results from deuterated water. Combining experiment and theory, we infer an intrinsic ICD lifetime of 12-52 fs for small water clusters.
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| 3. |
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| 4. |
- Schmid, Georg, et al.
(author)
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Tracing charge transfer in argon dimers by XUV-pump IR-probe experiments at FLASH
- 2019
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 151:8
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Journal article (peer-reviewed)abstract
- Charge transfer (CT) at avoided crossings of excited ionized states of argon dimers is observed using a two-color pump-probe experiment at the free-electron laser in Hamburg (FLASH). The process is initiated by the absorption of three 27-eV-photons from the pump pulse, which leads to the population of Ar2+*-Ar states. Due to nonadiabatic coupling between these one-site doubly ionized states and two-site doubly ionized states of the type Ar+*-Ar+, CT can take place leading to the population of the latter states. The onset of this process is probed by a delayed infrared (800 nm) laser pulse. The latter ionizes the dimers populating repulsive Ar2+ -Ar+ states, which then undergo a Coulomb explosion. From the delay-dependent yields of the obtained Ar2+ and Ar+ ions, the lifetime of the charge-transfer process is extracted. The obtained experimental value of (531 ± 136) fs agrees well with the theoretical value computed from Landau-Zener probabilities.
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