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  • 1.
    Anderson, Emma K.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Kamińska, Magdalena
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Jan Kochanowski University, Poland.
    Chartkunchand, Kiattichart C.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Eklund, Gustav
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Gatchell, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. University of Innsbruck, Austria.
    Hansen, K.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Decays of excited silver-cluster anions Agn, n=4 to 7, in the Double ElectroStatic Ion Ring ExpEriment2018Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 98, nr 2, artikel-id 022705Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Spontaneous decays of small, hot silver-cluster anions Ag-n(-), n = 4-7, have been studied using one of the rings of the Double ElectroStatic Ion Ring ExpEriment (DESIREE). Observation of these decays over very long time scales is possible due to the very low residual gas pressure (similar to 10(-14)) and cryogenic (13 K) operation of DESIREE. The yield of neutral particles from stored beams of Ag-6(-) and Ag-2(-) anions were measured for 100 milliseconds and were found to follow single power-law behavior with millisecond time-scale exponential cutoffs. The Ag-4(-) and Ag-5(-) anions were stored for 60 s and the observed decays show two-component power-law behaviors. We present calculations of the rate constants for electron detachment from and fragmentation of Ag-4(-) and Ag-5(-). In these calculations, we assume that the internal energy distribution of the clusters are flat and with this we reproduce the early steep parts of the experimentally measured decay curves for Ag-4(-) and Ag-5(-) which extends to tens and hundreds of milliseconds, respectively. The fact that the calculations reproduce the early slopes of Ag-4(-) and Ag-5(-), which differ for the two cases, suggests that it is the changes in fragmentation rates with internal cluster energies of Ag-4(-) and Ag-5(-) rather than conditions in the ion source that determine this behavior. Comparisons with the measurements strongly suggest that the neutral particles detected in these time domains originate from Ag-4(-) -> Ag-3(-) + Ag and Ag-5(-) -> Ag-3(-) +Ag-2 fragmentation processes.

  • 2.
    Anderson, Emma K.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt-May, Alice F.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Universität Innsbruck, Austria.
    Najeeb, Punnakayathil K.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Eklund, Gustav
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Chartkunchand, K. C.
    Rosén, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Larson, Åsa
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Hansen, K.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Spontaneous Electron Emission from Hot Silver Dimer Anions: Breakdown of the Born-Oppenheimer Approximation2020Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 124, nr 17, artikel-id 173001Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report the first experimental evidence of spontaneous electron emission from a homonuclear dimer anion through direct measurements of Ag-2(-) -> Ag-2 + e(-) decays on milliseconds and seconds timescales. This observation is very surprising as there is no avoided crossing between adiabatic energy curves to mediate such a process. The process is weak, yet dominates the decay signal after 100 ms when ensembles of internally hot Ag-2(-) ions are stored in the cryogenic ion-beam storage ring, DESIREE, for 10 s. The electron emission process is associated with an instantaneous, very large reduction of the vibrational energy of the dimer system. This represents a dramatic deviation from a Born-Oppenheimer description of dimer dynamics.

  • 3.
    Anderson, Emma K.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt-May, Alice F.
    Najeeb, Punnakayathil K.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Eklund, Gustav
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Chartkunchand, Kiattichart C.
    Rosén, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Kaminska, Magdalena
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Stockett, Mark H.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Nascimento, Rodrigo
    Hansen, Klavs
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Fragmentaion and detachemnt of hot silver and copper dimer anionsManuskript (preprint) (Övrigt vetenskapligt)
  • 4.
    Anderson, Emma K.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Aarhus University, Denmark.
    Schmidt-May, Alice Frederike
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Najeeb, P. K.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Eklund, Gustav
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Chartkunchand, K. C.
    Rosén, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Kamińska, Magdalena
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Stockett, Mark H.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Nascimento, R.
    Hansen, K.
    Larson, Åsa
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Fragmentation of and electron detachment from hot copper and silver dimer anions: A comparison2023Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 107, nr 6, artikel-id 062824Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We measured the spontaneous decays of internally hot copper and silver dimer anions, and , stored in one of the two ion-beam storage rings of the Double Electrostatic Ion Ring Experiment (DESIREE) at Stockholm University. A coincidence detection technique was utilized enabling essentially background-free measurements of -> Cu + Cu- and -> Ag + Ag- fragmentation rates. Furthermore, the total rates of neutral decay products (monomers and dimers) were measured and the relative contributions of fragmentation and electron emission ( -> Cu2 + e- and -> Ag2 + e-) were deduced as functions of storage time. Fragmentation is completely dominant at early times. However, after about 20 ms of storage, electron emission is observed and becomes the leading decay path after 100 ms for both dimer anions. The branching ratios between fragmentation and electron emission (vibrationally assisted autodetachment processes) are very nearly the same for and Ag-2 throughout the present storage cycle of 10 seconds. This is surprising considering the difference between the electron affinities of the neutral dimers, Cu2 and Ag2, and the difference between the and the dissociation energies.

  • 5. Aumayr, Friedrich
    et al.
    Ueda, Kiyoshi
    Sokell, Emma
    Schippers, Stefan
    Sadeghpour, Hossein
    Merkt, Frederic
    Gallagher, Thomas F.
    Dunning, F. Barry
    Scheier, Paul
    Eche, Olof
    Kirchner, Tom
    Fritzsche, Stephan
    Surzhykov, Andrey
    Ma, Xinwen
    Rivarola, Roberto
    Fojon, Omar
    Tribedi, Lokesh
    Lamour, Emily
    Lopez-Urrutia, Jose R. Crespo
    Litvinov, Yuri A.
    Shabaev, Vladimir
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schleberger, Marika
    Wilhelm, Richard A.
    Azuma, Toshiyuki
    Boduch, Philippe
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Stoehlker, Thomas
    Roadmap on photonic, electronic and atomic collision physics: III. Heavy particles2019Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 52, nr 17, artikel-id 171003Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We publish three Roadmaps on photonic, electronic and atomic collision physics in order to celebrate the 60th anniversary of the ICPEAC conference. Roadmap III focusses on heavy particles: with zero to relativistic speeds. Modern theoretical and experimental approaches provide detailed insight into the wide range of many-body interactions involving projectiles and targets of varying complexity ranging from simple atoms, through molecules and clusters, complex biomolecules and nanoparticles to surfaces and crystals. These developments have been driven by technological progress and future developments will expand the horizon of the systems that can be studied. This Roadmap aims at looking back along the road, explaining the evolution of the field, and looking forward, collecting nineteen contributions from leading scientists in the field.

  • 6. Barklem, Paul S
    et al.
    Amarsi, Anish M
    Grumer, Jon
    Eklund, Gustav
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Rosén, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Ji, MingChao
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Mutual neutralisation in Li++H/D and Na++H/D collisions: Implications of experimentalresults for non-LTE modelling of stellar spectraManuskript (preprint) (Övrigt vetenskapligt)
  • 7. Barklem, Paul S.
    et al.
    Amarsi, Anish M.
    Grumer, Jon
    Eklund, Gustav
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Rosén, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Ji, MingChao
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Mutual Neutralization in Li++H/D and Na++H/D Collisions: Implications of Experimental Results for Non-LTE Modeling of Stellar Spectra2021Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 908, nr 2, artikel-id 245Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Advances in merged-beams instruments have allowed experimental studies of the mutual neutralization (MN) processes in collisions of both Li+ and Na+ ions with D at energies below 1 eV. These experimental results place constraints on theoretical predictions of MN processes of Li+ and Na+ with H, important for non-LTE modeling of Li and Na spectra in late-type stars. We compare experimental results with calculations for methods typically used to calculate MN processes, namely the full quantum (FQ) approach, and asymptotic model approaches based on the linear combination of atomic orbitals (LCAO) and semiempirical (SE) methods for deriving couplings. It is found that FQ calculations compare best overall with the experiments, followed by the LCAO, and the SE approaches. The experimental results together with the theoretical calculations, allow us to investigate the effects on modeled spectra and derived abundances and their uncertainties arising from uncertainties in the MN rates. Numerical experiments in a large grid of 1D model atmospheres, and a smaller set of 3D models, indicate that neglect of MN can lead to abundance errors of up to 0.1 dex (26%) for Li at low metallicity, and 0.2 dex (58%) for Na at high metallicity, while the uncertainties in the relevant MN rates as constrained by experiments correspond to uncertainties in abundances of much less than 0.01 dex (2%). This agreement for simple atoms gives confidence in the FQ, LCAO, and SE model approaches to be able to predict MN with the accuracy required for non-LTE modeling in stellar atmospheres.

  • 8. Bernard, J.
    et al.
    Montagne, G.
    Bredy, R.
    Terpend-Ordaciere, B.
    Bourgey, A.
    Kerleroux, M.
    Chen, L.
    Schmidt, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Martin, S.
    A ""tabletop"" electrostatic ion storage ring: Mini-Ring2008Ingår i: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 79, nr 7, s. 75109-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report on the design, construction, and commissioning of a novel electrostatic ion storage ring of small dimensions-in the following referred to as ""Mini-Ring."" Mini-Ring consists of four horizontal parallel-plate deflectors and two conical electrostatic mirrors. Ions are injected through the two deflectors on the injection side and off axis with respect to the conical mirrors which face each other. The first injection deflector, originally at zero voltage, is switched to its set value such that the ions after one turn follow stable trajectories of lengths of roughly 30 cm. This design reduces the number of electrodes necessary to guide the ion beam through the ring in stable orbits. The six elements (deflectors and mirrors) are placed on a common grounded plate-the tabletop. Here, we present the design, ion trajectory simulations, and results of the first test experiments demonstrating the successful room-temperature operation of Mini-Ring at background pressures of 10(-6)-10(-7) mbar.

  • 9. Bernard, Jérôme
    et al.
    Ji, MingChao
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Indrajith, Suvasthika
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Stockett, Mark H.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Navarro-Navarrete, José E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Kono, Naoko
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Martin, Serge
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Efficient radiative cooling of tetracene cations C18H12+: absolute recurrent fluorescence rates as a function of internal energy2023Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 25, nr 15, s. 10726-10740Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have measured recurrent fluorescence (RF) cooling rates of internally hot tetracene cations, C18H12+, as functions of their storage times and internal energies in two different electrostatic ion-beam storage rings – the cryogenic ring DESIREE with a circumference of 8.6 meters in Stockholm and the much smaller room temperature ring Mini-Ring in Lyon, which has a circumference of 0.71 meters. The RF rates were measured to be as high as 150 to 1000 s−1 for internal energies in the 7 to 9.4 eV energy range, where we have probed the time evolution of the internal energy distribution with nanosecond laser pulses with a 1 kHz repetition rate. These RF rates are found to be significantly higher than those of previously investigated smaller PAHs such as e.g. anthracene and naphthalene, for which the lowest non-forbidden electronic excited state, the D2 state, is populated with a smaller probability by inverse internal conversion. Furthermore, the D2–D0 transition rate is smaller for these smaller molecules than for tetracene. The complementary features of the two storage rings allow for RF rate measurements in a broader internal energy range than has been possible before. The smaller sampling period of about 6 μs in Mini-Ring is ideal to study the cooling dynamics of the hotter ions that decay fast, whereas DESIREE with a sampling period of about 60 μs is better suited to study the colder ions that decay on longer timescales ranging up to hundreds of milliseconds. The excellent agreement between the two series of measurements in the region where they overlap demonstrates the complementarity of the two electrostatic ion-beam storage rings.

  • 10. Bernigaud, Virgile
    et al.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Haag, Nicole
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Holm, Anne I. S.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Huber, Bernd A.
    Hvelplund, Preben
    Kadhane, Umesh
    Larsen, Mikkel Koefod
    Manil, Bruno
    Nielsen, Steen Bröndsted
    Panja, Subhasis
    Ptasinska, Sylwia
    Rangama, Jimmy
    Reinhed, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Streletskii, Alexey V.
    Stöchkel, Kristian
    Worm, Esben S.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Electron capture-induced dissociation of AK dipeptide dications: Influence of ion velocity, crown-ether complexation and collision gas2008Ingår i: International Journal of Mass Spectrometry, ISSN 1387-3806, E-ISSN 1873-2798, Vol. 276, nr 2-3, s. 77-81Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The fragmentation of doubly protonated AK dipeptide ions has been investigated after collisional electron transfer. Electron capture leads to three dominant channels, H loss, NH3 loss, and N–Cα bond breakage to give either c+ or z+ fragment ions. The relative importance of these channels has been explored as a function of ion velocity, the degree of complexation with crown ether, and collision gas. Our results indicate that H loss and NH3 loss are competing channels whereas the probability of N–Cα bond breakage is more or less constant.

  • 11. Berrah, Nora
    et al.
    Fang, Li
    Murphy, Brendan
    Osipov, Timur
    Ueda, Kiyoshi
    Kukk, Edwin
    Feifel, Raimund
    van der Meulen, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Salén, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Thomas, Richard D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Larsson, Mats
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Richter, Robert
    Prince, Kevin C.
    Bozek, John D.
    Bostedt, Christoph
    Wada, Shin-ichi
    Piancastelli, Maria N.
    Tashiro, Motomichi
    Ehara, Masahiro
    Double-core-hole spectroscopy for chemical analysis with an intense X-ray femtosecond laser2011Ingår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 108, nr 41, s. 16912-16915Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Theory predicts that double-core-hole (DCH) spectroscopy can provide a new powerful means of differentiating between similar chemical systems with a sensitivity not hitherto possible. Although DCH ionization on a single site in molecules was recently measured with double-and single-photon absorption, double-core holes with single vacancies on two different sites, allowing unambiguous chemical analysis, have remained elusive. Here we report that direct observation of double-core holes with single vacancies on two different sites produced via sequential two-photon absorption, using short, intense X-ray pulses from the Linac Coherent Light Source free-electron laser and compare it with theoretical modeling. The observation of DCH states, which exhibit a unique signature, and agreement with theory proves the feasibility of the method. Our findings exploit the ultrashort pulse duration of the free-electron laser to eject two core electrons on a time scale comparable to that of Auger decay and demonstrate possible future X-ray control of physical inner-shell processes.

  • 12. Bull, James N.
    et al.
    Scholz, Michael S.
    Carrascosa, Eduardo
    Kristiansson, Moa K.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Eklund, Gustav
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Punnakayathil, Najeeb
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    de Ruette, Nathalie
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Stockett, Mark H.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Ultraslow radiative cooling of Cn- (n=3-5)2019Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 151, nr 11, artikel-id 114304Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ultraslow radiative cooling lifetimes and adiabatic detachment energies for three astrochemically relevant anions, Cn- (n = 3-5), are measured using the Double ElectroStatic Ion Ring ExpEriment (DESIREE) infrastructure at Stockholm University. DESIREE maintains a background pressure of approximate to 10(-14) mbar and temperature of approximate to 13 K, allowing storage of mass-selected ions for hours and providing conditions coined a molecular cloud in a box. Here, we construct two-dimensional (2D) photodetachment spectra for the target anions by recording photodetachment signal as a function of irradiation wavelength and ion storage time (seconds to minute time scale). Ion cooling lifetimes, which are associated with infrared radiative emission, are extracted from the 2D photodetachment spectrum for each ion by tracking the disappearance of vibrational hot-band signal with ion storage time, giving 1e cooling lifetimes of 3.1 +/- 0.1 s (C3-), 6.8 +/- 0.5 s (C4-), and 24 +/- 5 s (C5-). Fits of the photodetachment spectra for cold ions, i.e., those stored for at least 30 s, provide adiabatic detachment energies in good agreement with values from laser photoelectron spectroscopy on jet-cooled anions, confirming that radiative cooling has occurred in DESIREE. Ion cooling lifetimes are simulated using a simple harmonic cascade model, finding good agreement with experiment and providing a mode-by-mode understanding of the radiative cooling properties. The 2D photodetachment strategy and radiative cooling modeling developed in this study could be applied to investigate the ultraslow cooling dynamics of a wide range of molecular anions.

  • 13.
    Bäckström, Erik
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Hanstorp, D.
    Hole, Odd Magnar
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Kaminska, Magdalena
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Jan Kochanowski University, Poland.
    Nascimento, Rodrigo F.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Blom, Mikael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Björkhage, Mikael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Källberg, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Löfgren, Patrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Reinhed, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Rosén, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Simonsson, Ansgar
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Thomas, Richard D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Mannervik, Sven
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Storing keV negative ions for an hour: The lifetime of the metastable 2P1/2 level in 32S−2015Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 114, nr 14, artikel-id 143003Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We use a novel electrostatic ion storage ring to measure the radiative lifetime of the upper level in the 3p 5  P 2  o 1/2 →3p 5  P 2  o 3/2   spontaneous radiative decay in S −  32   to be 503±54  sec . This is by orders of magnitude the longest lifetime ever measured in a negatively charged ion. Cryogenic cooling of the storage ring gives a residual-gas pressure of a few times 10 −14   mbar at 13 K and storage of 10 keV sulfur anions for more than an hour. Our experimental results differ by 1.3σ  from the only available theoretical prediction.

  • 14.
    Chartkunchand, Kiattichart C.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Kaminska, Magdalena
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Jan Kochanowski University, Poland.
    Anderson, Emma K.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Kristiansson, M. K.
    Eklund, Gustav
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Hole, Odd Magnar
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Nascimento, Rodrigo F.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Centro Federal de Educação Tecnológica Celso Suckow da Fonseca, Brazil.
    Blom, Mikael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Björkhage, Mikael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Källberg, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Löfgren, Patrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Reinhed, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Rosén, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Simonsson, Ansgar
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Thomas, Richard D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Mannervik, Sven
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Davis, V. T.
    Neill, P. A.
    Thompson, J. S.
    Hanstorp, D.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Radiative lifetimes of the bound excited states of Pt-2016Ingår i: Physical Review A, ISSN 2469-9926, Vol. 94, nr 3, artikel-id 032501Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The intrinsic radiative lifetimes of the 5d(10)6s(2)S(1/2) and 5d(9)6s(2) D-2(3/2) bound excited states in the platinum anion Pt- have been studied at cryogenic temperatures at the Double ElectroStatic Ion Ring Experiment (DESIREE) facility at Stockholm University. The intrinsic lifetime of the higher-lying 5d(10)6s S-2(1/2) state was measured to be 2.54 +/- 0.10 s, while only a lifetime in the range of 50-200 ms could be estimated for the 5d(9)6s(2) D-2(3/2) fine-structure level. The storage lifetime of the Pt- ion beam was measured to be a little over 15 min at a ring temperature of 13 K. The present study reports the lifetime of an atomic negative ion in an excited bound state with an electron configuration different from that of the ground state.

  • 15.
    Chartkunchand, Kiattichart C.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Stockett, Mark H.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Anderson, Emma K.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Eklund, Gustav
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Kristiansson, Moa K.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Kamińska, Magdalena
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Jan Kochanowski University, Poland.
    de Ruette, Nathalie
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Blom, Mikael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Björkhage, Mikael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Källberg, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Löfgren, Patrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Reinhed, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Rosén, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Simonsson, Ansgar
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Dianion diagnostics in DESIREE: High-sensitivity detection of C-n(2-) from a sputter ion source2018Ingår i: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 89, nr 3, artikel-id 033112Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A sputter ion source with a solid graphite target has been used to produce dianions with a focus on carbon cluster dianions, C-n(2-), with n = 7-24. Singly and doubly charged anions from the source were accelerated together to kinetic energies of 10 keV per atomic unit of charge and injected into one of the cryogenic (13 K) ion-beam storage rings of the Double ElectroStatic Ion Ring Experiment facility at Stockholm University. Spontaneous decay of internally hot C-n(2-) dianions injected into the ring yielded C-n(2-) anions with kinetic energies of 20 keV, which were counted with a microchannel plate detector. Mass spectra produced by scanning the magnetic field of a 90 degrees analyzing magnet on the ion injection line reflect the production of internally hot C-7(2-) - C-24(2-) dianions with lifetimes in the range of tens of microseconds to milliseconds. In spite of the high sensitivity of this method, no conclusive evidence of C-6(2-) was found while there was a clear C-7(2-) signal with the expected isotopic distribution. This is consistent with earlier experimental studies and with theoretical predictions. An upper limit is deduced for a C-6(2-) signal that is two orders-of-magnitude smaller than that for C-7(2-). In addition, CnO2- and CnCu2- dianions were detected.

  • 16.
    Chen, Tao
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Gatchell, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Stockett, Mark H.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Alexander, John D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zhang, Y.
    Rousseau, P.
    Domaracka, A.
    Maclot, S.
    Delaunay, R.
    Adoui, L.
    Huber, B. A.
    Schlatholter, T.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Absolute fragmentation cross sections in atom-molecule collisions: Scaling laws for non-statistical fragmentation of polycyclic aromatic hydrocarbon molecules2014Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 140, nr 22, artikel-id 224306Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present scaling laws for absolute cross sections for non-statistical fragmentation in collisions between Polycyclic Aromatic Hydrocarbons (PAH/PAH(+)) and hydrogen or helium atoms with kinetic energies ranging from 50 eV to 10 keV. Further, we calculate the total fragmentation cross sections (including statistical fragmentation) for 110 eV PAH/PAH(+) + He collisions, and show that they compare well with experimental results. We demonstrate that non-statistical fragmentation becomes dominant for large PAHs and that it yields highly reactive fragments forming strong covalent bonds with atoms (H and N) and molecules (C6H5). Thus nonstatistical fragmentation may be an effective initial step in the formation of, e. g., Polycyclic Aromatic Nitrogen Heterocycles (PANHs). This relates to recent discussions on the evolution of PAHNs in space and the reactivities of defect graphene structures.

  • 17.
    Chen, Tao
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Gatchell, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Stockett, Mark H.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Rudy, Delaunay
    Domaracka, Alicja
    Micelotta, Elisabetta R.
    Tielens, Alexander G. G. M.
    Rousseau, Patrick
    Adoui, Lamri
    Huber, Bernd A.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Formation of H2 from internally heated polycyclic aromatic hydrocarbons: Excitation energy dependence2015Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 142, nr 14, artikel-id 144305Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have investigated the effectiveness of molecular hydrogen (H-2) formation from Polycyclic Aromatic Hydrocarbons (PAHs) which are internally heated by collisions with keV ions. The present and earlier experimental results are analyzed in view of molecular structure calculations and a simple collision model. We estimate that H-2 formation becomes important for internal PAH temperatures exceeding about 2200 K, regardless of the PAH size and the excitation agent. This suggests that keV ions may effectively induce such reactions, while they are unlikely due to, e.g., absorption of single photons with energies below the Lyman limit. The present analysis also suggests that H-2 emission is correlated with multi-fragmentation processes, which means that the [PAH-2H](+) peak intensities in the mass spectra may not be used for estimating H-2-formation rates.

  • 18.
    de Ruette, Nathalie
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Dochain, A.
    Launoy, T.
    Nascimento, Rodrigo F.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Centro Federal de Educação Tecnológica Celso Suckow da Fonseca, Brazil.
    Kaminska, Magdalena
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Jan Kochanowski University, Poland.
    Stockett, Mark H.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Vaeck, N.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Urbain, X.
    Mutual Neutralization of O- with O+ and N+ at Subthermal Collision Energies2018Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 121, nr 8, artikel-id 083401Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have measured total absolute cross sections for the mutual neutralization (MN) of O- with O+ and N+. A fine resolution (of about 50 meV) in the kinetic energy spectra of the product neutral atoms allows unique identification of the atomic states participating in the mutual neutralization process. Cross sections and branching ratios have also been calculated down to 1 meV center-of-mass collision energy for these two systems, with a multichannel Landau-Zener model and an asymptotic method for the ionic-covalent coupling matrix elements. The importance of two-electron processes in one-electron transfer is demonstrated by the dominant contribution of a core-excited configuration of the nitrogen atom in N+ + O- collisions. This effect is partially accounted for by introducing configuration mixing in the evaluation of coupling matrix elements.

  • 19.
    de Ruette, Nathalie
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Wolf, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Giacomozzi, Linda
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Alexander, John D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Gatchell, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Universität Innsbruck, Austria.
    Stockett, Mark H.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Haag, Nicole
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    DESIREE electrospray ion source test bench and setup for collision induced dissociation experiments2018Ingår i: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 89, nr 7, artikel-id 075102Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we give a detailed description of an electrospray ion source test bench and a single-pass setup for ion fragmentation studies at the Double ElectroStatic Ion Ring ExpEriment infrastructure at Stockholm University. This arrangement allows for collision-induced dissociation experiments at the center-of-mass energies between 10 eV and 1 keV. Charged fragments are analyzed with respect to their kinetic energies (masses) by means of an electrostatic energy analyzer with a wide angular acceptance and adjustable energy resolution.

  • 20.
    Eklund, Gustav
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Grumer, Jon
    Barklem, Paul S
    Rosén, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Ji, MingChao
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Simonsson, Ansgar
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Thomas, Richard D
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Final-state-resolved mutual neutralization of Na+ and D2020Manuskript (preprint) (Övrigt vetenskapligt)
  • 21.
    Eklund, Gustav
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Grumer, Jon
    Barklem, Paul S.
    Rosén, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Ji, MingChao
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Simonsson, Ansgar
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Thomas, Richard D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Final-state-resolved mutual neutralization of Na+ and D-2021Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 103, nr 3, artikel-id 032814Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The present paper reports on a merged-beam experiment on mutual neutralization between Na+ and D-. For this experiment, we have used the DESIREE ion-beams storage-ring facility. The reaction products are detected using a position- and time-sensitive detector, which ideally allows for determination of the population of each individual quantum state in the final atomic systems. Here, the 4s, 3d, and 4p final states in Na are observed and in all cases the D atom is in its ground state 1s S-2. The respective branching fractions of the states populated in Na are determined by fitting results from a Monte Carlo simulation of the experiment to the measured data. The center-of-mass collision energy is controlled using a set of biased drift tubes, and the branching fractions are measured for energies between 80 meV and 393 meV. The resulting branching fractions are found to agree qualitatively with the only available theoretical calculations for this particular system, which are based on a multichannel Landau-Zener approach using dynamic couplings determined with a linear combination of atomic orbitals model.

  • 22.
    Eklund, Gustav
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Grumer, Jon
    Rosén, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Ji, MingChao
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Punnakayathil, Najeeb
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Källberg, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Simonsson, Ansgar
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Thomas, Richard D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Stockett, Mark H.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Reinhed, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Löfgren, Patrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Björkhage, Mikael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Blom, Mikael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Barklem, Paul S.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cryogenic merged-ion-beam experiments in DESIREE: Final-state-resolved mutual neutralization of Li+ and D-2020Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 102, nr 1, artikel-id 012823Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have developed an experimental technique to study charge-and energy-flow processes in sub-eV collisions between oppositely charged, internally cold, ions of atoms, molecules, and clusters. Two ion beams are stored in separate rings of the cryogenic ion-beam storage facility DESIREE, and merged in a common straight section where a set of biased drift tubes is used to control the center-of-mass collision energy locally in fine steps. Here, we present measurements on mutual neutralization between Li+ and D- where a time-sensitive imaging-detector system is used to measure the three-dimensional distance between the neutral Li and D atoms as they reach the detector. This scheme allows for direct measurements of kinetic-energy releases, and here it reveals separate populations of the 3s state and the (3p + 3d) states in neutral Li while the D atom is left in its ground state 1s. The branching fraction of the 3s final state is measured to be 57.8 +/- 0.7% at a center-of-mass collision energy of 78 +/- 13 meV. The technique paves the way for studies of charge-, energy-, and mass-transfer reactions in single collisions involving molecular and cluster ions in well-defined quantum states.

  • 23.
    Eklund, Gustav
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Kristiansson, Moa
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Chartkunchand, K. C.
    Anderson, Emma K.
    Simpson, Malcolm
    Wester, Roland
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Geppert, Wolf D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Experimental lifetime of the a1Δ electronically excited state of CH2022Ingår i: Physical Review Research, E-ISSN 2643-1564, Vol. 4, nr 1, artikel-id L012016Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    By repeatedly probing the a1Δ excited state and the X3Σ ground-state populations in a beam of CH ions stored in a cryogenic ion-beam storage ring for 100 s, we extract an intrinsic lifetime of 14.9±0.5 s for this excited state. This is far longer than all earlier experimental and theoretical results, exposing large difficulties in measuring and calculating slow decays and the need for benchmark quality experiments.

  • 24.
    Fischer, D.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Gudmundsson, Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Berenyi, Zoltan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Haag, Nicole
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Johansson, Henrik A. B.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Misra, Deepankar
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Reinhed, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Kallberg, A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Manne Siegbahn-laboratoriet.
    Simonsson, Ansgar
    Stockholms universitet, Naturvetenskapliga fakulteten, Manne Siegbahn-laboratoriet.
    Stochkel, K.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, H. T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Manne Siegbahn-laboratoriet.
    Importance of Thomas single-electron transfer in fast p-He collisions2010Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 81, nr 1, s. 12714-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report experimental angular differential cross sections for nonradiative single-electron capture in p-He collisions (p + He -> H + He+) with a separate peak at the 0.47 mrad Thomas scattering angle for energies in the 1.3-12.5 MeV range. We find that the intensity of this peak scales with the projectile velocity as v(P)(-11). This constitutes the first experimental test of the prediction from 1927 by L. H. Thomas [Proc. R. Soc. 114, 561 (1927)]. At our highest energy, the peak at the Thomas angle contributes with 13.5% to the total integrated nonradiative single-electron capture cross section.

  • 25.
    Gatchell, Michael
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Universität Innsbruck, Austria.
    Ameixa, João
    Ji, MingChao
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Stockett, Mark H.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Simonsson, Ansgar
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Denifl, Stephan
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Survival of polycyclic aromatic hydrocarbon knockout fragments in the interstellar medium2021Ingår i: Nature Communications, E-ISSN 2041-1723, Vol. 12, nr 1, artikel-id 6646Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Laboratory studies play a crucial role in understanding the chemical nature of the interstellar medium (ISM), but the disconnect between experimental timescales and the timescales of reactions in space can make a direct comparison between observations, laboratory, and model results difficult. Here we study the survival of reactive fragments of the polycyclic aromatic hydrocarbon (PAH) coronene, where individual C atoms have been knocked out of the molecules in hard collisions with He atoms at stellar wind and supernova shockwave velocities. Ionic fragments are stored in the DESIREE cryogenic ion-beam storage ring where we investigate their decay for up to one second. After 10 ms the initially hot stored ions have cooled enough so that spontaneous dissociation no longer takes place at a measurable rate; a majority of the fragments remain intact and will continue to do so indefinitely in isolation. Our findings show that defective PAHs formed in energetic collisions with heavy particles may survive at thermal equilibrium in the interstellar medium indefinitely, and could play an important role in the chemistry in there, due to their increased reactivity compared to intact or photo-fragmented PAHs. Ion storage rings allow reactions to be studied over orders of magnitude in time, bridging the gap between typical experimental and astronomical timescales. Here the authors observe that polycyclic aromatic hydrocarbon fragments produced upon collision with He atoms at velocities typical of stellar winds and supernova shockwaves remain intact up to second timescales, thus may play an important role in interstellar chemistry.

  • 26.
    Gatchell, Michael
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Florin, Naemi
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Indrajith, Suvasthika
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Navarro-Navarrete, José E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Martini, Paul
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Ji, MingChao
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Reinhed, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Rosén, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Simonsson, Ansgar
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum, Manne Siegbahn-laboratoriet.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum, Manne Siegbahn-laboratoriet.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Stability of C59 Knockout Fragments from Femtoseconds to InfinityManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    We have studied the stability of C59 anions as a function of time, from their formation on femtosecond timescales to their stabilization on second timescales and beyond, using a combination of theory and experiments. The C59 fragments were produced in collisions between C60 fullerene anions and neutral helium gas at a velocity of 90 km/s (corresponding to a collision energy of 166 eV in the center-of-mass frame). The fragments were then stored in a cryogenic ion-beam storage ring at the DESIREE facility where they were followed for up to one minute. Classical molecular dynamics simulations were used to determine the reaction cross section and the excitation energy distributions of the products formed in these collisions. We found that about 15 percent of the C59 ions initially stored in the ring are intact after about 100 ms, and that this population then remains intact indefinitely. This means that C60 fullerenes exposed to energetic atoms and ions, such as stellar winds and shock waves, will produce stable, highly reactive products, like C59, that are fed into interstellar chemical reaction networks.

  • 27.
    Gatchell, Michael
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Rousseau, P.
    Domaracka, A.
    Stockett, Mark H.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Chen, Tao
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Chesnel, J. Y.
    Mery, A.
    Maclot, S.
    Adoui, L.
    Huber, B. A.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Ions colliding with mixed clusters of C-60 and coronene: Fragmentation and bond formation2014Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 90, nr 2, artikel-id 022713Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have studied collisions between 22.5 keV He2+ ions and mixed clusters [(C-60)(m)(C24H12)(n)] of m C-60 and n coronene molecules where m and n range up to about ten. Surprisingly, the cluster fragmentation behavior in distant collisions is dramatically different for pure coronene clusters (m = 0) and clusters containing a single C-60 molecule (m = 1). In the latter case, the clusters may be ionized without also being fragmented on the experimental time scale of tens of microseconds. This does not occur for pure coronene clusters, but is a main characteristic of pure fullerene clusters. For ion trajectories penetrating the mixed cluster, we observe covalent bond formations between C-59 or C-58 and C-60, but not between coronene fragments and C-60, or between C-60 fragments and coronene. These results are explained by means of classical molecular dynamics simulations of collisions inside the fragmenting mixed clusters.

  • 28.
    Gatchell, Michael
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Alexander, John D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Andler, Guillermo
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Björkhage, Mikael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Blom, Mikael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Brännholm, Lars
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Bäckström, Erik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Chen, Tao
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Geppert, Wolf
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Halldén, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Hanstorp, Dag
    Hellberg, Fredrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Källberg, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Larsson, Mats
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Leontein, Sven
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Liljeby, Leif
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Löfgren, Patrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Mannervik, Sven
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Paal, Andras
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Reinhed, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Rensfelt, Karl-Gunnar
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Rosén, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Seitz, Fabian
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Simonsson, Ansgar
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Stockett, Mark H.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Thomas, Richard D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    First results from the Double ElectroStatic Ion-Ring ExpEriment, DESIREE2014Ingår i: XXVIII International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC 2013), Institute of Physics (IOP), 2014, artikel-id 092003Konferensbidrag (Refereegranskat)
    Abstract [en]

    We have stored the first beams in one of the rings of the double electrostatic ion-storage ring, DESIREE at cryogenic and at room temperature conditions. At cryogenic operations the following parameters are found. Temperature; T= 13K, pressure; p <10(-13) mbar, initial number of stored ions; N > 10(7) and storage lifetime of a C-2(-) beam; tau = 450 S.

  • 29.
    Gatchell, Michael
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Thomas, Richard D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Rosén, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Reinhed, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Löfgren, Patrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Brännholm, Lars
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Blom, Mikael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Björkhage, Mikael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Bäckström, Erik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Alexander, John D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Leontein, Sven
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Hanstorp, D.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Liljeby, Leif
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Källberg, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Simonsson, Ansgar
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Hellberg, Fredrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Mannervik, Sven
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Larsson, Mats
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Geppert, Wolf D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Rensfelt, Karl-Gunnar
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Danared, Håkan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. European Spallation Source, Sweden.
    Paál, Andras
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Masuda, Masaharu
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Halldén, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Andler, Guillermo
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Stockett, Mark H.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Chen, Tao
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Källersjö, Gunnar
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Weimer, Jan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Hansen, K.
    Hartman, H.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Commissioning of the DESIREE storage rings - a new facility for cold ion-ion collisions2014Ingår i: XXVIII International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC 2013), Institute of Physics (IOP), 2014, artikel-id 012040Konferensbidrag (Refereegranskat)
    Abstract [en]

    We report on the ongoing commissioning of the Double ElectroStatic Ion Ring ExpEriment, DESIREE, at Stockholm University. Beams of atomic carbon anions (C-) and smaller carbon anion molecules (C-2(-), C-3(-), C-4(-) etc.) have been produced in a sputter ion source, accelerated to 10 keV or 20 keV, and stored successfully in the two electrostatic rings. The rings are enclosed in a common vacuum chamber cooled to below 13 Kelvin. The DESIREE facility allows for studies of internally relaxed single isolated atomic, molecular and cluster ions and for collision experiments between cat-and anions down to very low center-of-mass collision energies (meV scale). The total thermal load of the vacuum chamber at this temperature is measured to be 32 W. The decay rates of stored ion beams have two components: a non-exponential component caused by the space charge of the beam itself which dominates at early times and an exponential term from the neutralization of the beam in collisions with residual gas at later times. The residual gas limited storage lifetime of carbon anions in the symmetric ring is over seven minutes while the 1/e lifetime in the asymmetric ring is measured to be about 30 seconds. Although we aim to improve the storage in the second ring, the number of stored ions are now sufficient for many merged beams experiments with positive and negative ions requiring milliseconds to seconds ion storage.

  • 30.
    Gatchell, Michael
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Stockett, Mark H.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Aarhus University, Denmark.
    de Ruette, Nathalie
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Chen, Tao
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Giacomozzi, Linda
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Nascimento, Rodrigo F.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Wolf, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Anderson, Emma K.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Delaunay, R.
    Vizcaino, V.
    Rousseau, P.
    Adoui, L.
    Huber, B. A.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Failure of hydrogenation in protecting polycyclic aromatic hydrocarbons from fragmentation2015Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 92, nr 5, artikel-id 050702Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A recent study of soft x-ray absorption in native and hydrogenated coronene cations, C24H12+m + m = 0-7, led to the conclusion that additional hydrogen atoms protect (interstellar) polycyclic aromatic hydrocarbon (PAH) molecules from fragmentation [Reitsma et al., Phys. Rev. Lett. 113, 053002 (2014)]. The present experiment with collisions between fast (30-200 eV) He atoms and pyrene (C16H10+m +, m = 0, 6, and 16) and simulations without reference to the excitation method suggests the opposite. We find that the absolute carbon-backbone fragmentation cross section does not decrease but increases with the degree of hydrogenation for pyrene molecules.

  • 31.
    Gatchell, Michael
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Stockett, Mark
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Rousseau, P.
    Chen, Tao
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Kulyk, Kostiantyn
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Chesnel, J. Y.
    Domaracka, A.
    Méry, A.
    Maclot, S.
    Adoui, L.
    Stöchkel, K.
    Hvelplund, P.
    Wang, Y.
    Alcamí, M.
    Huber, B. A.
    Martín, F.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Non-statistical fragmentation of PAHs and fullerenes in collisions with atoms2014Ingår i: International Journal of Mass Spectrometry, ISSN 1387-3806, E-ISSN 1873-2798, Vol. 365, s. 260-265Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Non-statistical fragmentation processes may be important when Polycyclic Aromatic Hydrocarbon molecules (PAHs), fullerenes, or other large complex molecules collide with atoms and atomic ions. For collisions with hydrogen or helium this occurs for center-of-mass energies between a few tens to a few hundreds of electron volts and typically results in losses of single atoms. In such processes one forms much more reactive fragments than in statistical fragmentation, which instead are dominated by losses of C2- or C2H2-molecules (H-atoms) from fullerenes and PAHs, respectively. An enhanced reactivity has recently been demonstrated for van der Waals clusters of C60 molecules where prompt knockouts of single C-atoms from one of the fullerenes yield highly reactive C59+ fragments, which easily form covalent bonds with a C60 molecule inside the clusters

  • 32.
    Gatchell, Michael
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Seitz, Fabian
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Chen, Tao
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Alexander, John D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Stocket, Mark H.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Lawicki, A.
    Rangama, J.
    Rousseau, P.
    Capron, M.
    Maclot, S.
    Maisonny, R.
    Domaracka, A.
    Adoui, L.
    Mery, A.
    Chesnel, J-Y
    Manil, B.
    Huber, B. A.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Ions colliding with polycyclic aromatic hydrocarbon clusters2013Ingår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T156, s. 014062-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have measured the ionization and fragmentation of polycyclic aromatic hydrocarbon (PAH) molecules and their clusters. We find that PAH clusters containing up to roughly 100 individual molecules fragment strongly following collisions with keV ions in low or high charge states (q). For both types of collisions, singly charged PAH molecules are found to be the dominant products but for very different reasons. A high-q ion projectile charge leads to strong multiple ionization of the PAH clusters and subsequent Coulomb explosions. A low-q ion projectile charge often leads to single ionization but stronger internal heating and long evaporation sequences with a singly charged PAH monomer as the end product. We have developed a Monte Carlo method for collision-induced heating of PAH clusters and present an evaporation model where the clusters cool slowly as most of the internal energies are stored in intramolecular vibrations and not in molecule-molecule vibrations.

  • 33.
    Giacomozzi, Linda
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    D'Angelo, Giovanna
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Universidad Autónoma de Madrid, Spain.
    Diaz-Tendero, S.
    de Ruette, Nathalie
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Stockett, Mark H.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Alcami, M.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Decay pathways for protonated and deprotonated adenine molecules2019Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 151, nr 4, artikel-id 044306Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have measured fragment mass spectra and total destruction cross sections for protonated and deprotonated adenine following collisions with He at center-of-mass energies in the 20-240 eV range. Classical and ab initio molecular dynamics simulations are used to provide detailed information on the fragmentation pathways and suggest a range of alternative routes compared to those reported in earlier studies. These new pathways involve, for instance, losses of HNC molecules from protonated adenine and losses of NH2 or C3H2N2 from deprotonated adenine. The present results may be important to advance the understanding of how biomolecules may be formed and processed in various astrophysical environments.

  • 34.
    Giacomozzi, Linda
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    D'Angelo, Giovanna
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Diaz-Tendero, Sergio
    de Ruette, Nathalie
    Stockett, Mark
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Alcamí, Manuel
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Decay pathways for protonated and deprotonated Adenine moleculesManuskript (preprint) (Övrigt vetenskapligt)
  • 35.
    Giacomozzi, Linda
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Gatchell, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    de Ruette, Nathalie
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Wolf, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    D'Angelo, Giovanna
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Universidade do Porto, Portugal; Universidad Autónoma de Madrid, Spain.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Knockout driven fragmentation of porphyrins2017Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, nr 30, s. 19750-19755Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have studied collisions between tetraphenylporphyrin cations and He or Ne at center-of-mass energies in the range 50-110 eV. The experimental results were interpreted in view of density functional theory calculations of dissociation energies and classical molecular dynamics simulations of how the molecules respond to the He/Ne impact. We demonstrate that prompt atom knockout strongly contributes to the total destruction cross sections. Such impulse driven processes typically yield highly reactive fragments and are expected to be important for collisions with any molecular system in this collision energy range, but have earlier been very difficult to isolate for biomolecules.

  • 36. Gnaser, Hubert
    et al.
    Martschini, Martin
    Leimbach, David
    Karls, Julia
    Hanstorp, Dag
    Indrajith, Suvasthika
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Ji, MingChao
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Martini, Paul
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Simonsson, Ansgar
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Golser, Robin
    Spontaneous and photo-induced decay processes of WF5- and HfF5- molecular anions in a cryogenic storage ring2022Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 157, nr 4, artikel-id 044304Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Spontaneous and photo-induced decay processes of HfF5 and WF5 molecular anions were investigated in the Double ElectroStatic Ion Ring ExpEriment (DESIREE). The observation of these reactions over long time scales (several tens of ms) was possible due to the cryogenic temperatures (13 K) and the extremely low residual gas pressure (∼10−14 mbar) of DESIREE. For photo-induced reactions, laser wavelengths in the range 240 to 450 nm were employed. Both anion species were found to undergo spontaneous decay via electron detachment or fragmentation. After some ms, radiative cooling processes were observed to lower the probability for further decay through these processes. Photo-induced reactions indicate the existence of an energy threshold for WF5 anions at about 3.5 eV, above which the neutralization yield increases strongly. By contrast, HfF5 ions exhibit essentially no enhanced production of neutrals upon photon interaction, even for the highest photon energy used in this experiment (∼5.2 eV). This suppression will be highly beneficial for the efficient detection, in accelerator mass spectrometry, of the extremely rare isotope 182Hf using the 182HfF5 anion while effectively reducing the interfering stable isobar 182W in the analyte ion 182WF5. The radionuclide 182Hf is of great relevance in astrophysical environments as it constitutes a potential candidate to study the events of nucleosynthesis that may have taken place in the vicinity of the solar system several million years ago.

  • 37. Grumer, Jon
    et al.
    Eklund, Gustav
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Amarsi, Anish M
    Barklem, Paul S
    Rosén, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Ji, MingChao
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Simonsson, Ansgar
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Final-state resolved measurement of mutual neutralization in low-energy Mg+/D collisions: discrimination between theoretical predictions and impact on stellar spectral modelingManuskript (preprint) (Övrigt vetenskapligt)
  • 38. Grumer, Jon
    et al.
    Eklund, Gustav
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Amarsi, Anish M.
    Barklem, Paul S.
    Rosén, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Ji, MingChao
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Simonsson, Ansgar
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    State-Resolved Mutual Neutralization of Mg+ and D2022Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 128, nr 3, artikel-id 033401Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present experimental final-state distributions for Mg atoms formed in Mg++D− mutual neutralization reactions at center-of-mass collision energies of 59±12  meV by using the merged-beams method. Comparisons with available full-quantum results reveal large discrepancies and a previously underestimated total rate coefficient by up to a factor of 2 in the 0–1 eV (<104  K) regime. Asymptotic model calculations are shown to describe the process much better and we recommend applying this method to more complex iron group systems; data that is of urgent need in stellar spectral modeling.

  • 39.
    Gudmundsson, Magnus
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Fischer, D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Haag, N.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Johansson, H. A. B.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Misra, Deepankar
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Reinhed, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt-Boecking, H.
    Schuch, Reinhold
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schoeffler, M.
    Stochkel, K.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Angular scattering in fast ion-atom electron transfer collisions: projectile wave diffraction and Thomas mechanisms2010Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 43, nr 18, s. 185209-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report experimental angular differential cross sections for double-electron capture in He2+ + He collisions and single-electron capture in H+ + He collisions for the 1.3-12.5 MeV kinetic energy range. In all cases, the total cross sections are dominated by forward scattering peaks in d sigma/d Omega. The shapes and widths (but not the magnitudes) of these peaks are very similar for all energies and for capture of one or two electrons corresponding also to our measured linear increases in the transverse momentum transfers with increasing projectile velocities. These observations may be ascribed to diffraction limitations which are connected to electron transfer probabilities P(b) which are significant in limited regions of b only. For the H+ + He single-electron capture we observe two additional maxima in the angular differential cross sections. We conclude that while the secondary maxima at similar to 0.5 mrad probably have large contributions from the Thomas proton-electron-nucleus scattering mechanism, the third maxima at similar to 0.75 mrad are most likely mainly due to projectile de Broglie wave diffraction.

  • 40.
    Haag, Nicole
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Holm, Anne I. S.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Johansson, Henrik A. B.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Brøndsted Nielsen, Steen
    Hvelplund, Preben
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Electron capture induced dissociation of doubly protonated pentapeptides: Dependence on molecular structure and charge separation2011Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 134, nr 3, s. 035102-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have studied electron capture induced dissociation of a set of doubly protonated pentapeptides, all composed of one lysine (K) and either four glycine (G) or four alanine (A) residues, as a function of the sequence of these building blocks. Thereby the separation of the two charges, sequestered on the N-terminal amino group and the lysine side chain, is varied. The characteristic cleavage of N–Cα bonds is observed for all peptides over the whole backbone length, with the charge carrying fragments always containing K. The resulting fragmentation patterns are very similar if G is replaced by A. In the case of [XKXXX+2H]2+ (X=A or G), a distinct feature is observed in the distribution of backbone cleavage fragments and the probability for ammonia loss is drastically reduced. This may be due to an isomer with an amide oxygen as protonation site giving rise to the observed increase in breakage at a specific site in the molecule. For the other peptides, a correlation with the distance between amide oxygen and the charge at the lysine side chain has been found. This may be an indication that it is only the contribution from this site to the charge stabilization of the amide π* orbitals which determines relative fragment intensities. For comparison, complexes with two crown ether molecules have been studied as well. The crown ether provides a shielding of the charge and prevents the peptide from folding and internal hydrogen bonding, which leads to a more uniform fragmentation behavior.

  • 41.
    Haag, Nicole
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Liu, Bo
    Brøndsted Nielsen, Steen
    Zettergren, Henning
    Hvelplund, Preben
    Manil, Bruno
    Huber, Bernd A.
    Johansson, Henrik A. B.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Collisions with biomolecules embedded in smallwater clusters2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    We have studied fragmentation of water embedded adenosine 5’-monophosphate(AMP) anions after collisions with neutral sodium atoms. At a collision energy of 50 keV,loss of water molecules from the collisionally excited cluster ions is the dominant process andfragmentation of the AMP itself is almost completely prohibited if the number of attachedwater molecules is larger than 13. However, regardless of the initial number of water moleculesattached to the ion, capture of an electron, i.e. formation of a dianion, always leads to loss ofa single hydrogen atom accompanied by evaporation of water molecules. This damaging effectbecomes more important as the size of the water cluster increases, which is just the oppositeto the protective behavior observed for collision induced dissociation (CID) without electrontransfer. For both cases, the loss of water molecules within the experimental time frame isqualitatively well described by means of a common model of an evaporative ensemble. Thesesimulations, however, indicate that characteristically different distributions of internal energyare involved in CID and electron capture induced dissociation.

  • 42. Hansen, K.
    et al.
    Stockett, Mark H.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Aarhus University, Denmark.
    Kaminska, Magdalena
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Jan Kochanowski University, Poland.
    Nascimento, Rodrigo F.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Centro Federal de Educacao Tecnologica Celso Suckow da Fonseca, Brazil.
    Anderson, Emma K.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Gatchell, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Chartkunchand, Kiattichart C.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Eklund, Gustav
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Spontaneous decay of small copper-cluster anions Cu-n(-) (n=3-6), on long time scales2017Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 95, nr 2, artikel-id 022511Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have measured the spontaneous neutral particle emission from copper-cluster anions ( Cu-n(-), n = 3-6) stored at cryogenic temperatures in one of the electrostatic ion storage rings of the Double ElectroStatic Ion Ring ExpEriment facility at Stockholm University. The measured rate of emission from the stored Cu-3(-) ions follows a single power-law decay for about 1 ms but then decreases much more rapidly with time. The latter behavior may be due to a decrease in the density of available final states in Cu-3 as the excitation energies of the decaying ions approach the electron detachment threshold. The emissions from Cu-4(-), Cu-5(-), and Cu-6(-) are well described by sums of two power laws that are quenched by radiative cooling of the stored ions with characteristic times between a few and hundreds of milliseconds. We relate these two-component behaviors to populations of stored ions with higher and lower angular momenta. In a separate experiment, we studied the laser-induced decay of Cu-6(-) ions that were excited by 1.13- or 1.45-eV photons after 46 ms of storage.

  • 43.
    Holm, Anne I. S.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Johansson, Henrik A. B.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Seitz, Fabian
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Rosen, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Lawicki, A.
    Rangama, J.
    Rousseau, P.
    Capron, M.
    Maisonny, R.
    Adoui, L.
    Mery, A.
    Manil, B.
    Huber, B. A.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Ions Colliding with Cold Polycyclic Aromatic Hydrocarbon Clusters2010Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 105, nr 21, s. 213401-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report the first experimental study of ions interacting with clusters of polycyclic aromatic hydrocarbon (PAH) molecules. Collisions between 11.25 keV He-3(+) or 360 keV Xe-129(20+) and weakly bound clusters of one of the smallest PAH molecules, anthracene, show that C14H10 clusters have much higher tendencies to fragment in ion collisions than other weakly bound clusters. The ionization is dominated by peripheral collisions in which the clusters, very surprisingly, are more strongly heated by Xe20+ collisions than by He+ collisions. The appearance size is k = 15 for [C14H10](k)(2+).

  • 44.
    Johansson, Henrik A. B.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Holm, Anne I. S.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Haag, Nicole
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Brøndsted Nielsen, S.
    Wyer, J. A.
    Kirketerp, M.-B. S.
    Støchkel, K.
    Hvelplund, P.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Unimolecular dissociation of anthracene and acridine cations: The importance of isomerization barriers for the C2H2 loss and HCN loss channels2011Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 135, s. 084304-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The loss of C2H2 is a low activation energy dissociation channel for anthracene (C14H10) and acridine (C13H9N) cations. For the latter ion another prominent fragmentation pathway is the loss of HCN. We have studied these two dissociation channels by collision induced dissociation experiments of 50 keV anthracene cations and protonated acridine, both produced by electrospray ionization, in collisions with a neutral xenon target. In addition, we have carried out density functional theory calculations on possible reaction pathways for the loss of C2H2 and HCN. The mass spectra display features of multi-step processes, and for protonated acridine the dominant first step process is the loss of a hydrogen from the N site, which then leads to C2H2/HCN loss from the acridine cation. With our calculations we have identified three pathways for the loss of C2H2 from the anthracene cation, with three different cationic products: 2-ethynylnaphthalene, biphenylene, and acenaphthylene. The third product is the one with the overall lowest dissociation energy barrier. For the acridine cation our calculated pathway for the loss of C2H2 leads to the 3-ethynylquinoline cation, and the loss of HCN leads to the biphenylene cation. Isomerization plays an important role in the formation of the non-ethynyl containing products. All calculated fragmentation pathways should be accessible in the present experiment due to substantial energy deposition in the collisions.

  • 45.
    Johansson, Henrik A. B.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Holm, Anne I. S.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Seitz, Fabian
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Rousseau, P.
    Lawicki, A.
    Capron, M.
    Domaracka, A.
    Lattouf, E.
    Maclot, S.
    Maisonny, R.
    Manil, B.
    Chesnel, J.-Y.
    Adoui, L.
    Huber, B. A.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Ionization and fragmentation of polycyclic aromatic hydrocarbon clusters in collisions with keV ions2011Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 84, nr 4, s. 043201-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report on an experimental study of the ionization and fragmentation of clusters of k polycyclic aromatic hydrocarbon (PAH) molecules using anthracene, C14H10, or coronene, C24H12. These PAH clusters are moderately charged and strongly heated in small impact parameter collisions with 22.5-keV He2+ ions, after which they mostly decay in long monomer evaporation sequences with singly charged and comparatively cold monomers as dominating end products. We describe a simple cluster evaporation model and estimate the number of PAH molecules in the clusters that have to be hit by He2+ projectiles for such complete cluster evaporations to occur. Highly charged and initially cold clusters are efficiently formed in collisions with 360-keV Xe20+ ions, leading to cluster Coulomb explosions and several hot charged fragments, which again predominantly yield singly charged, but much hotter, monomer ions than the He2+ collisions. We present a simple formula, based on density-functional-theory calculations, for the ionization energy sequences as functions of coronene cluster size, rationalized in terms of the classic electrostatic expression for the ionization of a charged conducting object. Our analysis indicates that multiple electron removal by highly charged ions from a cluster of PAH molecules rapidly may become more important than single ionization as the cluster size k increases and that this is the main reason for the unexpectedly strong heating in these types of collisions.

  • 46.
    Kamińska, Magdalena
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Jan Kochanowski University, Poland.
    Davis, V. T.
    Hole, Odd Magnar
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Nascimento, Rodrigo F.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Centro Federal de Educação Tecnológica Celso Suckow da Fonseca, Brazil.
    Chartkunchand, Kiattichart C.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. University of Nevada, USA.
    Blom, Mikael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Björkhage, Mikael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Källberg, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Löfgren, Patrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Reinhed, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Rosén, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Simonsson, Ansgar
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Thomas, Richard D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Mannervik, Sven
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Neill, P. A.
    Thompson, J. S.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Hanstorp, D.
    Lifetime of the bound excited level in Ni-2016Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 93, nr 1, artikel-id 012512Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The intrinsic lifetime of the upper level in the bound-bound 3d(9) 4s(2) D-2(3/2) -> 3d(9) 4s(2) D-2(5/2) radiative transition in Ni- was measured to be 15.1 +/- 0.4 s. The experiment was performed at cryogenic temperatures in one of the ion-beam storage rings of the Double ElectroStatic Ion Ring ExpEriment facility at Stockholm University. The storage lifetime of the Ni- ion beam was measured to be close to 5 min at a ring temperature of 13 K.

  • 47.
    Kristiansson, Moa K.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Chartkunchand, Kiattichart
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. RIKEN, Japan.
    Eklund, Gustav
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Hole, Odd M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Anderson, Emma K.
    de Ruette, Nathalie
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Kamińska, Magdalena
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Punnakayathil, Najeeb
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Navarro-Navarrete, José E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Sigurdsson, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Grumer, Jon
    Simonsson, Ansgar
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Björkhage, Mikael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Rosén, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Reinhed, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Blom, Mikael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Källberg, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Alexander, John D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Hanstorp, Dag
    High-precision electron affinity of oxygen2022Ingår i: Nature Communications, E-ISSN 2041-1723, Vol. 13, nr 1, artikel-id 5906Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Negative ions are important in many areas of science and technology, e.g., in interstellar chemistry, for accelerator-based radionuclide dating, and in anti-matter research. They are unique quantum systems where electron-correlation effects govern their properties. Atomic anions are loosely bound systems, which with very few exceptions lack optically allowed transitions. This limits prospects for high-resolution spectroscopy, and related negative-ion detection methods. Here, we present a method to measure negative ion binding energies with an order of magnitude higher precision than what has been possible before. By laser-manipulation of quantum-state populations, we are able to strongly reduce the background from photodetachment of excited states using a cryogenic electrostatic ion-beam storage ring where keV ion beams can circulate for up to hours. The method is applicable to negative ions in general and here we report an electron affinity of 1.461 112 972(87) eV for 16O.

  • 48.
    Kristiansson, Moa K.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Karls, J.
    Gibson, N. D.
    Hanstorp, D.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Walter, C. W.
    Measurement of the lifetime of a metastable excited state in Bi2022Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 105, nr 1, artikel-id L010801Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The lifetime of the 3P0 state of Bi has been measured by selective photodetachment in a cryogenic ion-beam storage ring. By measuring the lifetime as a function of applied laser powers and extrapolating to zero laser power, a lifetime of 16.0±0.5 s is deduced for electric quadrupole decay of the excited state to the ground sate. The result provides a stringent test of recent state-of-the art theoretical calculations.

  • 49.
    Kristiansson, Moa K.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schiffmann, S.
    Grumer, J.
    Karls, J.
    de Ruette, Nathalie
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. European Spallation Source ERIC (ESS), Sweden.
    Eklund, Gustav
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Ideböhn, V.
    Gibson, N. D.
    Brage, T.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Hanstorp, D.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Experimental and theoretical studies of excited states in Ir-2021Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 103, nr 6, artikel-id 062806Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The properties of atomic negative ions are to a large extent determined by electron-electron correlation which makes them an ideal testing ground for atomic many-body physics. In this paper, we present a detailed experimental and theoretical study of excited states in the negative ion of iridium. The ions were stored at cryogenic temperatures using the double electrostatic ion ring experiment facility at Stockholm University. Laser photodetachment was used to monitor the relaxation of three bound excited states belonging to the [Xe] 4f(14)5d(8)6s(2) ionic ground configuration. Our measurements show that the first excited state has a lifetime much longer than the ion-beam storage time of 1230 +/- 100 s. The binding energy of this state was measured to be 1.045 +/- 0.002 eV. The lifetimes of the second and third excited states were experimentally determined to be 133 +/- 10 and 172 +/- 35 ms, respectively. Multiconfiguration Dirac-Hartree-Fock calculations were performed in order to extract binding energies and lifetimes. These calculations predict the existence of the third excited bound state that was detected experimentally. The computed lifetimes for the three excited bound states agree well with the experimental results and allow for a clear identification of the detected levels.

  • 50.
    Kulyk, Kostiantyn
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Rebrov, Oleksii
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Stockett, Mark H.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Alexander, John D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Thomas, Richard D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Larsson, Mats
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    High-energy collisions of protonated enantiopure amino acids with a chiral target gas2015Ingår i: International Journal of Mass Spectrometry, ISSN 1387-3806, E-ISSN 1873-2798, Vol. 388, s. 59-64Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have studied the fragmentation of the singly protonated L- and D-forms of enantiomerically pure phenylalanine (Phe), tryptophan (Trp), and methionine (Met) in high-energy collisions with chiral and achiral gas targets. (S)-(+)-2-butanol, racemic (+/-)-2-butanol, and argon were used as target gases. At center-of-mass frame collision energy of I key, it was found that all of the ions exhibit common fragmentation pathways which are independent of target chirality. For all projectile ions, the elimination of NH3 and H2O + CO were found to be the main reaction channels. The observed fragmentation patterns were dominated by statistically driven processes. The energy deposited into the ions was found to be sufficient to yield multiple fragment ions, which arise from decomposition via various competitive reaction pathways.

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