| 1. |
- Gopakumar, Geethanjali, 1992-, et al.
(författare)
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Non-local decay of highly charged aqueous inorganic ions produced by Auger decay
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- High-Z atoms are more important for biological radiation damage by photons than their low abundance due to their higher photoionization cross-section. Using the inorganic Mg 2+ and Al3+ ions in water as model systems, we have studied decay processes following deep core-level ionization. Local Auger decay rapidly produces highly charged Mg 4+and Al5+ ions, the decay of which must involve non-local processes involving the surrounding water, such as electron transfer mediated decay (ETMD). Using electron spectroscopy we observe two distinct ETMD decay steps for Al, corresponding to decay from Al5+ to Al4+, and then from Al4+ to Al3+. The ETMD energetics is discussed using both a simple model and calculations. Contrary to expectations, we do not observe any ETMD for Mg, and possible reasons for this are discussed.
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| 2. |
- Gopakumar, Geethanjali, 1992-, et al.
(författare)
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Probing Aqueous Ions with Non-local Auger Relaxation
- 2022
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 24:15, s. 8661-8671
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Tidskriftsartikel (refereegranskat)abstract
- The decay of core holes is often regarded as a local process, but in some systems, it involves the autoionization of neighbouring atoms or molecules. Here, we explore such non-local autoionization (Intermolecular Coulombic Decay, ICD) of surrounding molecules upon 1s ionization of aqueous-phase Na+, Mg2+ and Al3+ ions. The three ions are isoelectronic but differ in the strength of the ion-water interactions which is manifested in experimental Auger electron spectra by varying intensities. While for strongly interacting Mg2+ and Al3+ the non-local decay is observed, for weakly bound Na+ no signal was measured. Combined with theoretical simulations we provide a microscopic understanding of the non-local decay processes. We assigned the ICD to decay processes ending with two-hole states delocalized between the central ion and neighbouring water. The ICD process is also shown to be highly selective with respect to water molecular orbitals. The ICD lifetime was estimated to be around 40 fs for Mg and 20 fs for Al. Auger spectroscopy thus represents a novel tool for exploring molecules in the liquid phase, providing simultaneously structural and electronic information.
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| 3. |
- Gopakumar, G., et al.
(författare)
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Radiation damage by extensive local water ionization from two-step electron-transfer-mediated decay of solvated ions
- 2023
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Ingår i: Nature Chemistry. - : Nature Publishing Group. - 1755-4330 .- 1755-4349. ; 15:10, s. 1408-1414
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Tidskriftsartikel (refereegranskat)abstract
- Biomolecular radiation damage is largely mediated by radicals and low-energy electrons formed by water ionization rather than by direct ionization of biomolecules. It was speculated that such an extensive, localized water ionization can be caused by ultrafast processes following excitation by core-level ionization of hydrated metal ions. In this model, ions relax via a cascade of local Auger–Meitner and, importantly, non-local charge- and energy-transfer processes involving the water environment. Here, we experimentally and theoretically show that, for solvated paradigmatic intermediate-mass Al3+ ions, electronic relaxation involves two sequential solute–solvent electron transfer-mediated decay processes. The electron transfer-mediated decay steps correspond to sequential relaxation from Al5+ to Al3+ accompanied by formation of four ionized water molecules and two low-energy electrons. Such charge multiplication and the generated highly reactive species are expected to initiate cascades of radical reactions. [Figure not available: see fulltext.]
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| 4. |
- Gopakumar, Geethanjali, et al.
(författare)
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X-ray-induced attosecond ion-water electron dynamics of aqueous ions
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The foundation of many physical and chemical processes is the transfer of charge from one entity to another. In many cases, the charge transfer is mediated by electron transfer and due to the comparatively low mass of electrons, these processes tend to take place within a few femtoseconds or several attoseconds. We investigate the charge transfer from Na+, Mg2+ and Al3+ in an aqueous environment to neighbouring water molecules. In order to achieve this, we use the core-hole clock method and Auger spectroscopy upon 1s ionization of the respective ions. The charge transfer times range from several 100 as below the 1s ionization threshold to only 20 as far above the 1s ionization. The decrease in charge transfer times as a function of the photon energy seems to be continuous. Despite the ions being isoelectronic in our study, we nd differences in their charge transfer behaviour.
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