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  • 1. Kivimaki, Antti
    et al.
    Stråhlman, Christian
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Sankari, Rami
    Richter, Robert
    Negative-ion/positive-ion coincidence spectroscopy as a tool to identify anionic fragments: The case of core-excited CHF32020In: Journal of Mass Spectrometry, ISSN 1076-5174, E-ISSN 1096-9888, Vol. 55, no 5, article id e4487Article in journal (Refereed)
    Abstract [en]

    We have studied the dissociation of the trifluoromethane molecule, CHF3, into negative ionic fragments at the C 1s and F 1s edges. The measurements were performed by detecting coincidences between negative and positive ions. We observed five different negative ions: F-, H-, C-, CF-, and F-2(-). Their production was confirmed by the analysis of triple coincidence events (negative-ion/positive-ion/positive-ion or NIPIPI coincidences) that were recorded with cleaner signals than those of the negative-ion/positive-ion coincidences. The intensities of the most intense NIPIPI coincidence channels were recorded as a function of photon energy across the C 1s and F 1s excitations and ionization thresholds. We also observed dissociation channels involving the formation of one negative ion and three positive ions. Our results demonstrate that negative-ion/positive-ion coincidence spectroscopy is a very sensitive method to observe anions, which at inner-shell edges are up to three orders of magnitude less probable dissociation products than cations.

  • 2. Kivimäki, Antti
    et al.
    Stråhlman, Christian
    Malmö University, Joint University Administration and Services.
    Richter, Robert
    Sankari, Rami
    Fragmentation of Methanol Molecules after Core Excitation and Core Ionization Studied by Negative-Ion/Positive-Ion Coincidence Experiments2018In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 122, no 1, p. 224-233Article in journal (Refereed)
    Abstract [en]

    We have studied the fragmentation of the methanol molecule after core excitation and core ionization by observing coincidences between negative and positive ions. Five different negative ions – H-, C-, CH-, O-, and OH- – were observed at both the C 1s and O 1s edges. As negative ion formation occurs after resonant and normal Auger decay of core-hole states, it is necessarily linked with the release of positively charged fragments. Our data show that such fragmentation can happen in many different ways: We found approximately 30 negative-ion/positive-ion/positive-ion coincidence (NIPIPICO) channels. All involve only singly charged positive ions. Fragmentation channels leading to atomic ions are the most probable, but positive molecular ions are also frequently found in the context of anion formation. Coincidence yields as a function of photon energy were determined for the most intense NIPIPICO channels. Adding together the data measured at different photon energies, we could also verify the occurrence of four-ion coincidences, which involved one negative ion (H- or O-) and three positive ions.

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  • 3.
    Kukk, Edwin
    et al.
    Department of Physics and Astronomy, University of Turku, Finland; CNRS, Laboratoire de Chimie Physique, France.
    Pihlava, Lassi
    Department of Physics and Astronomy, University of Turku, Finland.
    Kooser, Kuno
    Department of Physics and Astronomy, University of Turku, Finland; Institute of Physics, University of Tartu,Estonia.
    Stråhlman, Christian
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Maclot, Sylvain
    Department of Physics, Gothenburg University.
    Kivimäki, Antti
    MAX IV Laboratory, Lund University,.
    Energy-dependent timescales in the dissociation of diiodothiophene dication.2023In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 25, no 7, p. 5795-5807Article in journal (Refereed)
    Abstract [en]

    Photodissociation molecular dynamics of gas-phase 2,5-diiodothiophene molecules was studied in an electron-energy-resolved electron-multi-ion coincidence experiment performed at the FinEstBeAMS beamline of MAX IV synchrotron. Following the photoionization of the iodine 4d subshell and the Auger decay, the dissociation landscape of the molecular dication was investigated as a function of the Auger electron energy. Concentrating on an major dissociation pathway, C4H2I2S2+ → C4H2S+ + I+ + I, and accessing the timescales of the process via ion momentum correlation analysis, it was revealed how this three-body process changes depending on the available internal energy. Using a generalized secondary dissociation model, the process was shown to evolve from secondary dissociation regime towards concerted dissociation as the available energy increased, with the secondary dissociation time constant changing from 1.5 ps to 129 fs. The experimental results were compared with simulations using a stochastic charge-hopping molecular mechanics model. It represented the observed trend and also gave a fair quantitative agreement with the experiment.

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  • 4. Kühn, Danilo
    et al.
    Sorgenfrei, Florian
    Giangrisostomi, Erika
    Jay, Raphael
    Musazay, Abdurrahman
    Ovsyannikov, Ruslan
    Stråhlman, Christian
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Svensson, Svante
    Mårtensson, Nils
    Föhlisch, Alexander
    Capabilities of Angle Resolved Time of Flight electron spectroscopy with the 60 degrees wide angle acceptance lens2018In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 224, p. 45-50Article in journal (Refereed)
    Abstract [en]

    The simultaneous detection of energy, momentum and temporal information in electron spectroscopy is the key aspect to enhance the detection efficiency in order to broaden the range of scientific applications. Employing a novel 60 degrees wide angle acceptance lens system, based on an additional accelerating electron optical element, leads to a significant enhancement in transmission over the previously employed 30 degrees electron lenses. Due to the performance gain, optimized capabilities for time resolved electron spectroscopy and other high transmission applications with pulsed ionizing radiation have been obtained. The energy resolution and transmission have been determined experimentally utilizing BESSY II as a photon source. Four different and complementary lens modes have been characterized. (C) 2017 The Authors. Published by Elsevier B.V.

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  • 5.
    Pihlava, Lassi
    et al.
    Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland.
    Berholts, Marta
    Institute of Physics, University of Tartu, EE-50411 Tartu, Estonia.
    Niskanen, Johannes
    Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland.
    Vladyka, Anton
    Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland.
    Kooser, Kuno
    Institute of Physics, University of Tartu, EE-50411 Tartu, Estonia.
    Stråhlman, Christian
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Eng-Johnsson, Per
    Department of Physics, Lund University, Lund.
    Kivimäki, Antti
    MAX IV Laboratory, Lund University, Lund.
    Kukk, Edwin
    Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland; Laboratoire de Chimie Physique-Matière et Rayonnement, UMR 7614, CNRS, Sorbonne University, FR-75005 Paris, France.
    Photodissociation of bromine-substituted nitroimidazole radiosensitizers2023In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 25, no 18, p. 13004-13011Article in journal (Refereed)
    Abstract [en]

    Heavy elements and some nitroimidazoles both exhibit radiosensitizing properties through different mechanisms. In an effort to see how the overall radiosensitivity might be affected when the two radiosensitizers are combined in the same molecule, we studied the gas-phase photodissociation of two brominated nitroimidazoles and a bromine-free reference sample. Synchrotron radiation was employed to initiate the photodynamics and energy-resolved multiparticle coincidence spectroscopy was used to study the ensuing dissociation. We observed the brominated samples releasing high amounts of potentially radiosensitizing fragments upon dissociation. Since bromination also increases the likelihood of the drug molecule being ionised per a given X-ray dose, we conclude that heavy-element substitution of nitroimidazoles appears to be a viable path towards new, potent radiosensitizer drugs.

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  • 6.
    Pihlava, Lassi
    et al.
    Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland.
    Niskanen, Johannes
    Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland.
    Kooser, Kuno
    Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland;Institute of Physics, University of Tartu, W. Ostwaldi 1, EE-50411 Tartu, Estonia.
    Stråhlman, Christian
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Maclot, Sylvain
    Department of Physics, Gothenburg University, Box 100, SE-40530 Gothenburg, Sweden.
    Kivimäki, Antti
    MAX IV Laboratory, Lund University, SE-22100 Lund, Sweden;Nano and Molecular Systems Research Unit, University of Oulu, FI-90570 Oulu, Finland.
    Kukk, Edwin
    Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland.
    Photodissociation dynamics of halogenated aromatic molecules: the case of core-ionized tetrabromothiophene2021In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 23, p. 21249-21261, article id 21249Article in journal (Refereed)
    Abstract [en]

    We studied the gas-phase photodissociation of a fully halogenated aromatic molecule,tetrabromothiophene, upon core–shell ionization by using synchrotron radiation and energy-resolvedmultiparticle coincidence spectroscopy. Photodynamics was initiated by the selective soft X-rayionization of three elements – C, S, and Br – leading to the formation of dicationic states by Augerdecay. From a detailed study of photodissociation upon Br 3d ionization, we formulate a generalfragmentation scheme, where dissociation into neutral fragments and a pair of cations prevails, butdicationic species are also produced. We conclude that dicationic tetrabromothiophene typically undergoesdeferred charge separation (with one of the ions being often Br+) that may be followed by secondarydissociation steps, depending on the available internal energy of the parent dication. Observations suggestthat the ejection of neutral bromine atoms as the first step of deferred charge separation is a prevailingfeature in dicationic dissociation, although sometimes in this step the C–Br bonds appear to remain intactand the thiophene ring is broken instead. Ionization-site-specific effects are observed particularly in doublycharged fragments and as large differences in the yields of the intact parent dication. We interpret theseeffects, using first-principles calculations and molecular dynamics simulations of core-hole states, as likelycaused by the geometry changes during the core-hole lifetime.

  • 7. Sankari, Anna
    et al.
    Stråhlman, Christian
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Sankari, Rami
    Partanen, Leena
    Laksman, Joakim
    Kettunen, J. Antti
    Galvan, Ignacio Fdez.
    Lindh, Roland
    Malmqvist, Per-Åke
    Sorensen, Stacey L.
    Non-radiative decay and fragmentation in water molecules after 1a1-1 4a1 excitation and core ionization studied by electron-energy-resolved electron--ion coincidence spectroscopy2020In: The Journal of Chemical Physics, Vol. 152, no 7, article id 074302Article in journal (Refereed)
    Abstract [en]

    In this paper, we examine decay and fragmentation of core-excited and core-ionized water molecules combining quantum chemical calculations and electron-energy-resolved electron–ion coincidence spectroscopy. The experimental technique allows us to connect electronic decay from core-excited states, electronic transitions between ionic states, and dissociation of the molecular ion. To this end, we calculate the minimum energy dissociation path of the core-excited molecule and the potential energy surfaces of the molecular ion. Our measurements highlight the role of ultra-fast nuclear motion in the 1a1−14a1" role="presentation" style="display: inline; line-height: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative;">1a−114a11a1−14a1 core-excited molecule in the production of fragment ions. OH+ fragments dominate for spectator Auger decay. Complete atomization after sequential fragmentation is also evident through detection of slow H+ fragments. Additional measurements of the non-resonant Auger decay of the core-ionized molecule (1a1−1" role="presentation" style="display: inline; line-height: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative;">1a−111a1−1) to the lower-energy dication states show that the formation of the OH+ + H+ ion pair dominates, whereas sequential fragmentation OH+ + H+ → O + H+ + H+ is observed for transitions to higher dication states, supporting previous theoretical investigations.

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  • 8.
    Stråhlman, Christian
    et al.
    Malmö högskola, Joint University Administration and Services.
    Kivimäki, Antti
    Richter, Robert
    Sankari, Rami
    Negative- and positive-ion fragmentation of core-excited formic-acid molecules studied with three- and four-ion coincidence spectroscopy2017In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 96, no 2, article id 023409Article in journal (Refereed)
    Abstract [en]

    The negative-ion fragmentation of formic acid (HCOOH) is studied with negative- and positive-ion coincidence spectroscopy. We report four-body ionic fragmentation where up to three positive ions are collected in coincidence with one negative ion. We report yields for 21 three-body channels and five four-body channels. More than 80% of all negative-ion fragmentation involves production of O-, and it is dominated by complete dissociation of all molecular bonds. Negative-ion creation is most abundant at high-Rydberg resonances and just above the molecule's core-ionization potentials. The existence of four-body fragmentation channels evidences a strong charge redistribution in the molecule.

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  • 9.
    Stråhlman, Christian
    et al.
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Moog, Bruno
    Ertan, Emelie
    Odelius, Michael
    Kivimäki, Antti
    Richter, Robert
    Sankari, Rami
    Selective negative-ion formation from core-valence doubly excited states of the water molecule2018In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 98, no 5, article id 053432Article in journal (Refereed)
    Abstract [en]

    This study focuses on the role of negative-ion formation in the decay of core-valence doubly excited water molecules. Combining negative- and positive-ion coincidence measurements with calculated energies of core-valence doubly excited states, we find that O− and H− production is enhanced selectively. In particular, we suggest that O− production is correlated to double occupancy of the antibonding 4a1 virtual orbital, while H− appears at electronic states with double occupancy in 2b2. We also show that H− and O− can be created as a result of electron recapture close to the O 1s ionization potential.

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