| 1. |
- Kjellsson, Ludvig
(författare)
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X-ray spectroscopy on diatomic and cationic molecules
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- X-ray spectroscopy have been used to study the electronic structure of diatomic and cationic molecules. X-ray absorption spectra of the molecular cations N2+, O2+, and CO+ have been measured. The spectra are vibrationally resolved and are analyzed with theoretical and semi-empirical methods determining spectroscopic constants of core-excited states. Ionization of water have been studied by time resolved X-ray absorption spectroscopy. The evolution of the absorption spectrum gives an estimate of the formation time of the aqueous hydroxyl radical and an estimate of the upper limit of the lifetime of H2O+. The aqueous hydroxyl radical has been studied by resonant inelastic X-ray scattering. The experiment is suggesting that the electronic structure of the OH-radical is not heavily affected upon solvation. Resonant inelastic X-ray scattering spectra at the π*-resonance of N2 have been recorded and are analyzed within the Kramers-Heisenberg framework, emphasizing the importance of lifetime-vibrational interference. The spectra of N2 show states populated by radiative electron rearrangement and due to their repulsiveness the features images the vibrational wavefunctions of the intermediate state.
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| 2. |
- Kumagai, Yoshiaki, et al.
(författare)
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Suppression of thermal nanoplasma emission in clusters strongly ionized by hard x-rays
- 2021
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Ingår i: Journal of Physics B. - : Institute of Physics Publishing (IOPP). - 0953-4075 .- 1361-6455. ; 54:4
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Tidskriftsartikel (refereegranskat)abstract
- Using electron and ion spectroscopy, we studied the electron and nuclear dynamics in similar to 50 000-atom large krypton clusters, following excitation with an intense hard x-ray pulse. Beyond the single pulse experiment, we also present the results of a time-resolved, x-ray pump-near-infrared probe measurement that allows one to learn about the time evolution of the system. After core ionization of the atoms by x-ray photons, trapped Auger and secondary electrons form a nanoplasma in which the krypton ions are embedded, according to the already published scenario. While the ion data show expected features, the electron emission spectra miss the expected pump-probe delay-dependent enhancement except for a slight enhancement in the energy range below 2 eV. Theoretical simulations help to reveal that, due to the deep trapping potential of the ions during the long time expansion accompanied by electron-ion recombination, thermal emission from the transient nanoplasma becomes quenched.
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| 3. |
- Mattioli, Giuseppe, et al.
(författare)
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Unravelling molecular interactions in uracil clusters by XPS measurements assisted by ab initio and tight-binding simulations
- 2020
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Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- The C, N and O 1s XPS spectra of uracil clusters in the gas phase have been measured. A new bottom-up approach, which relies on computational simulations starting from the crystallographic structure of uracil, has been adopted to interpret the measured spectra. This approach sheds light on the different molecular interactions (H-bond, pi -stacking, dispersion interactions) at work in the cluster and provides a good understanding of the observed XPS chemical shifts with respect to the isolated molecule in terms of intramolecular and intermolecular screening occurring after the core-hole ionization. The proposed bottom-up approach, reasonably expensive in terms of computational resources, has been validated by finite-temperature molecular dynamics simulations of clusters composed of up to fifty molecules.
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| 4. |
- Travnikova, Oksana, et al.
(författare)
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Dynamics of core-excited ammonia : disentangling fragmentation pathways by complementary spectroscopic methods
- 2023
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 25:2, s. 1063-1074
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Tidskriftsartikel (refereegranskat)abstract
- Fragmentation dynamics of core-excited isolated ammonia molecules is studied by two different and complementary experimental methods, high-resolution resonant Auger spectroscopy and electron energy-selected Auger electron-photoion coincidence spectroscopy (AEPICO). The combined use of these two techniques allows obtaining information on different dissociation patterns, in particular fragmentation before relaxation, often called ultrafast dissociation (UFD), and fragmentation after relaxation. The resonant Auger spectra contain the spectral signature of both molecular and fragment final states, and therefore can provide information on all events occurring during the core-hole lifetime, in particular fragmentation before relaxation. Coincidence measurements allow correlating Auger electrons with ionic fragments from the same molecule, and relating the ionic fragments to specific Auger final electronic states, and yield additional information on which final states are dissociative, and which ionic fragments can be produced in timescales either corresponding to the core-hole lifetime or longer. Furthermore, we show that by the combined use of two complementary experimental techniques we are able to identify more electronic states of the NH2+ fragment with respect to the single one already reported in the literature.
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