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  • 1.
    Anderson, Emma K.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Kamińska, Magdalena
    Stockholm University, Faculty of Science, Department of Physics. Jan Kochanowski University, Poland.
    Chartkunchand, Kiattichart C.
    Stockholm University, Faculty of Science, Department of Physics.
    Eklund, Gustav
    Stockholm University, Faculty of Science, Department of Physics.
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics. University of Innsbruck, Austria.
    Hansen, K.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Decays of excited silver-cluster anions Ag-n, n=4 to 7, in the Double ElectroStatic Ion Ring ExpEriment2018In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 98, no 2, article id 022705Article in journal (Refereed)
    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.
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt-May, Alice F.
    Najeeb, Punnakayathil K.
    Stockholm University, Faculty of Science, Department of Physics.
    Eklund, Gustav
    Stockholm University, Faculty of Science, Department of Physics.
    Chartkunchand, Kiattichart C.
    Rosén, Stefan
    Stockholm University, Faculty of Science, Department of Physics.
    Kaminska, Magdalena
    Stockholm University, Faculty of Science, Department of Physics.
    Stockett, Mark H.
    Stockholm University, Faculty of Science, Department of Physics.
    Nascimento, Rodrigo
    Hansen, Klavs
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Fragmentaion and detachemnt of hot silver and copper dimer anionsManuscript (preprint) (Other academic)
  • 3. 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
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Schleberger, Marika
    Wilhelm, Richard A.
    Azuma, Toshiyuki
    Boduch, Philippe
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Stoehlker, Thomas
    Roadmap on photonic, electronic and atomic collision physics: III. Heavy particles2019In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 52, no 17, article id 171003Article in journal (Refereed)
    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.

  • 4. Bernard, J.
    et al.
    Montagne, G.
    Bredy, R.
    Terpend-Ordaciere, B.
    Bourgey, A.
    Kerleroux, M.
    Chen, L.
    Schmidt, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Martin, S.
    A ""tabletop"" electrostatic ion storage ring: Mini-Ring2008In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 79, no 7, p. 75109-Article in journal (Refereed)
    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.

  • 5. Bernigaud, Virgile
    et al.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Haag, Nicole
    Stockholm University, Faculty of Science, Department of Physics.
    Holm, Anne I. S.
    Stockholm University, Faculty of Science, Department of Physics.
    Huber, Bernd A.
    Hvelplund, Preben
    Kadhane, Umesh
    Larsen, Mikkel Koefod
    Manil, Bruno
    Nielsen, Steen Bröndsted
    Panja, Subhasis
    Ptasinska, Sylwia
    Rangama, Jimmy
    Reinhed, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Streletskii, Alexey V.
    Stöchkel, Kristian
    Worm, Esben S.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Electron capture-induced dissociation of AK dipeptide dications: Influence of ion velocity, crown-ether complexation and collision gas2008In: International Journal of Mass Spectrometry, ISSN 1387-3806, E-ISSN 1873-2798, Vol. 276, no 2-3, p. 77-81Article in journal (Refereed)
    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.

  • 6.
    Bäckström, Erik
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Hanstorp, D.
    Hole, Odd Magnar
    Stockholm University, Faculty of Science, Department of Physics.
    Kaminska, Magdalena
    Stockholm University, Faculty of Science, Department of Physics. Jan Kochanowski University, Poland.
    Nascimento, Rodrigo F.
    Stockholm University, Faculty of Science, Department of Physics.
    Blom, Mikael
    Stockholm University, Faculty of Science, Department of Physics.
    Björkhage, Mikael
    Stockholm University, Faculty of Science, Department of Physics.
    Källberg, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Löfgren, Patrik
    Stockholm University, Faculty of Science, Department of Physics.
    Reinhed, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Rosén, Stefan
    Stockholm University, Faculty of Science, Department of Physics.
    Simonsson, Ansgar
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Mannervik, Sven
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Storing keV negative ions for an hour: The lifetime of the metastable 2P1/2 level in 32S−2015In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 114, no 14, article id 143003Article in journal (Refereed)
    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.

  • 7.
    Chartkunchand, Kiattichart C.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Kaminska, Magdalena
    Stockholm University, Faculty of Science, Department of Physics. Jan Kochanowski University, Poland.
    Anderson, Emma K.
    Stockholm University, Faculty of Science, Department of Physics.
    Kristiansson, M. K.
    Eklund, Gustav
    Stockholm University, Faculty of Science, Department of Physics.
    Hole, Odd Magnar
    Stockholm University, Faculty of Science, Department of Physics.
    Nascimento, Rodrigo F.
    Stockholm University, Faculty of Science, Department of Physics. Centro Federal de Educação Tecnológica Celso Suckow da Fonseca, Brazil.
    Blom, Mikael
    Stockholm University, Faculty of Science, Department of Physics.
    Björkhage, Mikael
    Stockholm University, Faculty of Science, Department of Physics.
    Källberg, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Löfgren, Patrik
    Stockholm University, Faculty of Science, Department of Physics.
    Reinhed, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Rosén, Stefan
    Stockholm University, Faculty of Science, Department of Physics.
    Simonsson, Ansgar
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Mannervik, Sven
    Stockholm University, Faculty of Science, Department of Physics.
    Davis, V. T.
    Neill, P. A.
    Thompson, J. S.
    Hanstorp, D.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Radiative lifetimes of the bound excited states of Pt-2016In: Physical Review A, ISSN 2469-9926, Vol. 94, no 3, article id 032501Article in journal (Refereed)
    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.

  • 8.
    Chartkunchand, Kiattichart C.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Stockett, Mark H.
    Stockholm University, Faculty of Science, Department of Physics.
    Anderson, Emma K.
    Stockholm University, Faculty of Science, Department of Physics.
    Eklund, Gustav
    Stockholm University, Faculty of Science, Department of Physics.
    Kristiansson, Moa K.
    Stockholm University, Faculty of Science, Department of Physics.
    Kamińska, Magdalena
    Stockholm University, Faculty of Science, Department of Physics. Jan Kochanowski University, Poland.
    de Ruette, Nathalie
    Stockholm University, Faculty of Science, Department of Physics.
    Blom, Mikael
    Stockholm University, Faculty of Science, Department of Physics.
    Björkhage, Mikael
    Stockholm University, Faculty of Science, Department of Physics.
    Källberg, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Löfgren, Patrik
    Stockholm University, Faculty of Science, Department of Physics.
    Reinhed, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Rosén, Stefan
    Stockholm University, Faculty of Science, Department of Physics.
    Simonsson, Ansgar
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Dianion diagnostics in DESIREE: High-sensitivity detection of C-n(2-) from a sputter ion source2018In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 89, no 3, article id 033112Article in journal (Refereed)
    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.

  • 9.
    Chen, Tao
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Alexander, John D.
    Stockholm University, Faculty of Science, Department of Physics.
    Forsberg, Björn
    Stockholm University, Faculty of Science, Department of Physics.
    Pettersson, Alf
    Stockholm University, Faculty of Science, Department of Physics.
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Modeling electron and energy transfer processes in collisions between ions and Polycyclic Aromatic Hydrocarbon molecules2014In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 488, p. 102015-Article in journal (Refereed)
    Abstract [en]

    In this work we study collisions between ions and Polycyclic Aromatic Hydrocarbons with the aid of a novel over-the-barrier model and well-established models for nuclear and electronic stopping processes.

  • 10.
    Chen, Tao
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Stockett, Mark H.
    Stockholm University, Faculty of Science, Department of Physics.
    Alexander, John D.
    Stockholm University, Faculty of Science, Department of Physics.
    Zhang, Y.
    Rousseau, P.
    Domaracka, A.
    Maclot, S.
    Delaunay, R.
    Adoui, L.
    Huber, B. A.
    Schlatholter, T.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Absolute fragmentation cross sections in atom-molecule collisions: Scaling laws for non-statistical fragmentation of polycyclic aromatic hydrocarbon molecules2014In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 140, no 22, article id 224306Article in journal (Refereed)
    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.

  • 11.
    Chen, Tao
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Stockett, Mark H.
    Stockholm University, Faculty of Science, Department of Physics.
    Rudy, Delaunay
    Domaracka, Alicja
    Micelotta, Elisabetta R.
    Tielens, Alexander G. G. M.
    Rousseau, Patrick
    Adoui, Lamri
    Huber, Bernd A.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Formation of H2 from internally heated polycyclic aromatic hydrocarbons: Excitation energy dependence2015In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 142, no 14, article id 144305Article in journal (Refereed)
    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.

  • 12. da Silva, Humberto, Jr.
    et al.
    Oller, Javier
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Stockett, Mark H.
    Stockholm University, Faculty of Science, Department of Physics.
    Hervieux, Paul-Antoine
    Adoui, Lamri
    Alcami, Manuel
    Huber, Bernd A.
    Martin, Fernando
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Rousseau, Patrick
    Diaz-Tendero, Sergio
    Multiple electron capture, excitation, and fragmentation in C6+-C-60 collisions2014In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 90, no 3, p. 032701-Article in journal (Refereed)
    Abstract [en]

    We present experimental and theoretical results on single- and multiple-electron capture, and fragmentation, in C6+ + C-60 collisions at velocities in the v(col) = 0.05 - 0.4 a.u. range. We use time-of-flight mass spectrometry and coincidence detection of charged fragments to separate pure target ionization from processes in which the C-60 target is both ionized and fragmented. The coincidence technique allows us to identify different types of fragmentation processes such as C-60(q+) -> C-58(q+) + C-2 and C-60(q+) -> C-58((q-1)+) + C-2(+). A quasimolecular approach is employed to calculate charge transfer and target excitation cross sections. First-order time-dependent perturbation and statistical methods are used to treat the postcollisional processes: the calculated rate constants for C-2 and C-2(+) emission from the excited and charged fullerene are then used to evaluate the fragmentation dynamics. We show that the target ionization cross section decreases with the induced target charge state and the impact energy. C-2 emission from C-60(q+) is found to dominate when q <= 2 while C-2(+) emission dominates when q >= 5, in agreement with the present and previous experimental results.

  • 13.
    de Ruette, Nathalie
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Dochain, A.
    Launoy, T.
    Nascimento, Rodrigo F.
    Stockholm University, Faculty of Science, Department of Physics. Centro Federal de Educação Tecnológica Celso Suckow da Fonseca, Brazil.
    Kaminska, Magdalena
    Stockholm University, Faculty of Science, Department of Physics. Jan Kochanowski University, Poland.
    Stockett, Mark H.
    Stockholm University, Faculty of Science, Department of Physics.
    Vaeck, N.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Urbain, X.
    Mutual Neutralization of O- with O+ and N+ at Subthermal Collision Energies2018In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 121, no 8, article id 083401Article in journal (Refereed)
    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.

  • 14.
    de Ruette, Nathalie
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Wolf, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Giacomozzi, Linda
    Stockholm University, Faculty of Science, Department of Physics.
    Alexander, John D.
    Stockholm University, Faculty of Science, Department of Physics.
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics. Universität Innsbruck, Austria.
    Stockett, Mark H.
    Stockholm University, Faculty of Science, Department of Physics.
    Haag, Nicole
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    DESIREE electrospray ion source test bench and setup for collision induced dissociation experiments2018In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 89, no 7, article id 075102Article in journal (Refereed)
    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.

  • 15. Delaunay, R.
    et al.
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Mika, A.
    Domaracka, A.
    Adoui, L.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Rousseau, P.
    Huber, B. A.
    Shock-driven formation of covalently bound carbon nanoparticles from ion collisions with clusters of C-60 fullerenes2018In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 129, p. 766-774Article in journal (Refereed)
    Abstract [en]

    We show that the energetic processing of C-60 clusters by slow atomic projectiles leads to ultrafast (< ps) formation of large covalent carbon nanoparticles containing a few hundreds of atoms. The underlying mechanism is found to be due to impulse-driven collisions between the projectile and the nuclei of the molecules. Experimental findings are well reproduced by classical molecular dynamics simulations. The cross sections for molecular growth processes forming covalent systems which contain more than 60 carbon atoms are about 5.10(-14) cm(2) representing more than 70% of the geometrical cross sections. This demonstrates the high efficiency of the underlying processes. The formed carbon nanoparticles contain both aromatic and aliphatic structures which have also been considered as dust components in space.

  • 16. Domaracka, Alicja
    et al.
    Delaunay, Rudy
    Mika, Arkadiusz
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Rousseau, Patrick
    Huber, Bernd A.
    Ion collision-induced chemistry in pure and mixed loosely bound clusters of coronene and C-60 molecules2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 22, p. 15052-15060Article in journal (Refereed)
    Abstract [en]

    Ionization, fragmentation and molecular growth have been studied in collisions of 22.5 keV He2+-or 3 keV Ar+-projectiles with pure loosely bound clusters of coronene (C24H12) molecules or with loosely bound mixed C-60-C24H12 clusters by using mass spectrometry. The heavier and slower Ar+ projectiles induce prompt knockout-fragmentation - C- and/or H-losses - from individual molecules and highly efficient secondary molecular growth reactions before the clusters disintegrate on picosecond timescales. The lighter and faster He2+ projectiles have a higher charge and the main reactions are then ionization by ions that are not penetrating the clusters. This leads mostly to cluster fragmentation without molecular growth. However, here penetrating collisions may also lead to molecular growth but to a much smaller extent than with 3 keV Ar+. Here we present fragmentation and molecular growth mass distributions with 1 mass unit resolution, which reveals that the same numbers of C- and H-atoms often participate in the formation and breaking of covalent bonds inside the clusters. We find that masses close to those with integer numbers of intact coronene molecules, or with integer numbers of both intact coronene and C-60 molecules, are formed where often one or several H-atoms are missing or have been added on. We also find that super-hydrogenated coronene is formed inside the clusters.

  • 17.
    Fischer, D.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Gudmundsson, Magnus
    Stockholm University, Faculty of Science, Department of Physics.
    Berenyi, Zoltan
    Stockholm University, Faculty of Science, Department of Physics.
    Haag, Nicole
    Stockholm University, Faculty of Science, Department of Physics.
    Johansson, Henrik A. B.
    Stockholm University, Faculty of Science, Department of Physics.
    Misra, Deepankar
    Stockholm University, Faculty of Science, Department of Physics.
    Reinhed, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Kallberg, A.
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Simonsson, Ansgar
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Stochkel, K.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, H. T.
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Importance of Thomas single-electron transfer in fast p-He collisions2010In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 81, no 1, p. 12714-Article in journal (Refereed)
    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.

  • 18.
    Forsberg, B. O.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Alexander, John D.
    Stockholm University, Faculty of Science, Department of Physics.
    Chen, Tao
    Stockholm University, Faculty of Science, Department of Physics.
    Pettersson, A. T.
    Stockholm University, Faculty of Science, Department of Physics.
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Ions interacting with planar aromatic molecules: Modeling electron transfer reactions2013In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 138, no 5, p. 054306-Article in journal (Refereed)
    Abstract [en]

    We present theoretical absolute charge exchange cross sections for multiply charged cations interacting with the Polycyclic Aromatic Hydrocarbon (PAH) molecules pyrene C14H10, coronene C24H12, or circumcoronene C54H18. These planar, nearly circular, PAHs are modelled as conducting, infinitely thin, and perfectly circular discs, which are randomly oriented with respect to straight line ion trajectories. We present the analytical solution for the potential energy surface experienced by an electron in the field of such a charged disc and a point-charge at an arbitrary position. The location and height of the corresponding potential energy barrier from this simple model are in close agreement with those from much more computationally demanding Density Functional Theory (DFT) calculations in a number of test cases. The model results compare favourably with available experimental data on single-and multiple electron transfer reactions and we demonstrate that it is important to include the orientation dependent polarizabilities of the molecules (model discs) in particular for the larger PAHs. PAH ionization energy sequences from DFT are tabulated and used as model inputs. Absolute cross sections for the ionization of PAH molecules, and PAH ionization energies such as the ones presented here may be useful when considering the roles of PAHs and their ions in, e. g., interstellar chemistry, stellar atmospheres, and in related photoabsorption and photoemission spectroscopies.

  • 19.
    Gatchell, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Delaunay, Rudy
    D'Angelo, Giovanna
    Stockholm University, Faculty of Science, Department of Physics. Universidade do Porto, Portugal; Universidad Autónoma de Madrid, Spain.
    Mika, Arkadiusz
    Kulyk, Kostiantyn
    Stockholm University, Faculty of Science, Department of Physics.
    Domaracka, Alicja
    Rousseau, Patrick
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Huber, Bernd A.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Ion-induced molecular growth in clusters of small hydrocarbon chains2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 30, p. 19665-19672Article in journal (Refereed)
    Abstract [en]

    We report on studies of collisions between 3 keV Ar+ projectile ions and neutral targets of isolated 1,3-butadiene (C4H6) molecules and cold, loosely bound clusters of these molecules. We identify molecular growth processes within the molecular clusters that appears to be driven by knockout processes and that could result in the formation of (aromatic) ring structures. These types of reactions are not unique to specific projectile ions and target molecules, but will occur whenever atoms or ions with suitable masses and kinetic energies collide with aggregates of matter, such as carbonaceous grains in the interstellar medium or aerosol nanoparticles in the atmosphere.

  • 20.
    Gatchell, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Rousseau, P.
    Domaracka, A.
    Stockett, Mark H.
    Stockholm University, Faculty of Science, Department of Physics.
    Chen, Tao
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Chesnel, J. Y.
    Mery, A.
    Maclot, S.
    Adoui, L.
    Huber, B. A.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Ions colliding with mixed clusters of C-60 and coronene: Fragmentation and bond formation2014In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 90, no 2, article id 022713Article in journal (Refereed)
    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.

  • 21.
    Gatchell, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Alexander, John D.
    Stockholm University, Faculty of Science, Department of Physics.
    Andler, Guillermo
    Stockholm University, Faculty of Science, Department of Physics.
    Björkhage, Mikael
    Stockholm University, Faculty of Science, Department of Physics.
    Blom, Mikael
    Stockholm University, Faculty of Science, Department of Physics.
    Brännholm, Lars
    Stockholm University, Faculty of Science, Department of Physics.
    Bäckström, Erik
    Stockholm University, Faculty of Science, Department of Physics.
    Chen, Tao
    Stockholm University, Faculty of Science, Department of Physics.
    Geppert, Wolf
    Stockholm University, Faculty of Science, Department of Physics.
    Halldén, Per
    Stockholm University, Faculty of Science, Department of Physics.
    Hanstorp, Dag
    Hellberg, Fredrik
    Stockholm University, Faculty of Science, Department of Physics.
    Källberg, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Leontein, Sven
    Stockholm University, Faculty of Science, Department of Physics.
    Liljeby, Leif
    Stockholm University, Faculty of Science, Department of Physics.
    Löfgren, Patrik
    Stockholm University, Faculty of Science, Department of Physics.
    Mannervik, Sven
    Stockholm University, Faculty of Science, Department of Physics.
    Paal, Andras
    Stockholm University, Faculty of Science, Department of Physics.
    Reinhed, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Rensfelt, Karl-Gunnar
    Stockholm University, Faculty of Science, Department of Physics.
    Rosén, Stefan
    Stockholm University, Faculty of Science, Department of Physics.
    Seitz, Fabian
    Stockholm University, Faculty of Science, Department of Physics.
    Simonsson, Ansgar
    Stockholm University, Faculty of Science, Department of Physics.
    Stockett, Mark H.
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    First results from the Double ElectroStatic Ion-Ring ExpEriment, DESIREE2014In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 488, p. 092003-Article in journal (Refereed)
    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.

  • 22.
    Gatchell, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Rosén, Stefan
    Stockholm University, Faculty of Science, Department of Physics.
    Reinhed, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Löfgren, Patrik
    Stockholm University, Faculty of Science, Department of Physics.
    Brännholm, Lars
    Stockholm University, Faculty of Science, Department of Physics.
    Blom, Mikael
    Stockholm University, Faculty of Science, Department of Physics.
    Björkhage, Mikael
    Stockholm University, Faculty of Science, Department of Physics.
    Bäckström, Erik
    Stockholm University, Faculty of Science, Department of Physics.
    Alexander, John D.
    Stockholm University, Faculty of Science, Department of Physics.
    Leontein, Sven
    Stockholm University, Faculty of Science, Department of Physics.
    Hanstorp, D.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Liljeby, Leif
    Stockholm University, Faculty of Science, Department of Physics.
    Källberg, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Simonsson, Ansgar
    Stockholm University, Faculty of Science, Department of Physics.
    Hellberg, Fredrik
    Stockholm University, Faculty of Science, Department of Physics.
    Mannervik, Sven
    Stockholm University, Faculty of Science, Department of Physics.
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Geppert, Wolf D.
    Stockholm University, Faculty of Science, Department of Physics.
    Rensfelt, Karl-Gunnar
    Stockholm University, Faculty of Science, Department of Physics.
    Danared, Håkan
    Stockholm University, Faculty of Science, Department of Physics. European Spallation Source, Sweden.
    Paál, Andras
    Stockholm University, Faculty of Science, Department of Physics.
    Masuda, Masaharu
    Stockholm University, Faculty of Science, Department of Physics.
    Halldén, Per
    Stockholm University, Faculty of Science, Department of Physics.
    Andler, Guillermo
    Stockholm University, Faculty of Science, Department of Physics.
    Stockett, Mark H.
    Stockholm University, Faculty of Science, Department of Physics.
    Chen, Tao
    Stockholm University, Faculty of Science, Department of Physics.
    Källersjö, Gunnar
    Stockholm University, Faculty of Science, Department of Physics.
    Weimer, Jan
    Stockholm University, Faculty of Science, Department of Physics.
    Hansen, K.
    Hartman, H.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Commissioning of the DESIREE storage rings - a new facility for cold ion-ion collisions2014In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 488, p. 012040-Article in journal (Refereed)
    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.

  • 23.
    Gatchell, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Stockett, Mark H.
    Stockholm University, Faculty of Science, Department of Physics. Aarhus University, Denmark.
    de Ruette, Nathalie
    Stockholm University, Faculty of Science, Department of Physics.
    Chen, Tao
    Stockholm University, Faculty of Science, Department of Physics.
    Giacomozzi, Linda
    Stockholm University, Faculty of Science, Department of Physics.
    Nascimento, Rodrigo F.
    Stockholm University, Faculty of Science, Department of Physics.
    Wolf, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Anderson, Emma K.
    Stockholm University, Faculty of Science, Department of Physics.
    Delaunay, R.
    Vizcaino, V.
    Rousseau, P.
    Adoui, L.
    Huber, B. A.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Failure of hydrogenation in protecting polycyclic aromatic hydrocarbons from fragmentation2015In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 92, no 5, article id 050702Article in journal (Refereed)
    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.

  • 24.
    Gatchell, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Stockett, Mark
    Stockholm University, Faculty of Science, Department of Physics.
    Rousseau, P.
    Chen, Tao
    Stockholm University, Faculty of Science, Department of Physics.
    Kulyk, Kostiantyn
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    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
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Non-statistical fragmentation of PAHs and fullerenes in collisions with atoms2014In: International Journal of Mass Spectrometry, ISSN 1387-3806, E-ISSN 1873-2798, Vol. 365, p. 260-265Article in journal (Refereed)
    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

  • 25.
    Gatchell, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Seitz, Fabian
    Stockholm University, Faculty of Science, Department of Physics.
    Chen, Tao
    Stockholm University, Faculty of Science, Department of Physics.
    Alexander, John D.
    Stockholm University, Faculty of Science, Department of Physics.
    Stocket, Mark H.
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    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
    Stockholm University, Faculty of Science, Department of Physics.
    Ions colliding with polycyclic aromatic hydrocarbon clusters2013In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T156, p. 014062-Article in journal (Refereed)
    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.

  • 26.
    Giacomozzi, Linda
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    D'Angelo, Giovanna
    Stockholm University, Faculty of Science, Department of Physics. Universidad Autónoma de Madrid, Spain.
    Diaz-Tendero, S.
    de Ruette, Nathalie
    Stockholm University, Faculty of Science, Department of Physics.
    Stockett, Mark H.
    Stockholm University, Faculty of Science, Department of Physics.
    Alcami, M.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Decay pathways for protonated and deprotonated adenine molecules2019In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 151, no 4, article id 044306Article in journal (Refereed)
    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.

  • 27.
    Giacomozzi, Linda
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    D'Angelo, Giovanna
    Stockholm University, Faculty of Science, Department of Physics.
    Diaz-Tendero, Sergio
    de Ruette, Nathalie
    Stockett, Mark
    Stockholm University, Faculty of Science, Department of Physics.
    Alcamí, Manuel
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Decay pathways for protonated and deprotonated Adenine moleculesManuscript (preprint) (Other academic)
  • 28.
    Giacomozzi, Linda
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    de Ruette, Nathalie
    Stockholm University, Faculty of Science, Department of Physics.
    Wolf, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    D'Angelo, Giovanna
    Stockholm University, Faculty of Science, Department of Physics. Universidade do Porto, Portugal; Universidad Autónoma de Madrid, Spain.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Knockout driven fragmentation of porphyrins2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 30, p. 19750-19755Article in journal (Refereed)
    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.

  • 29.
    Gudmundsson, Magnus
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Fischer, D.
    Stockholm University, Faculty of Science, Department of Physics.
    Haag, N.
    Stockholm University, Faculty of Science, Department of Physics.
    Johansson, H. A. B.
    Stockholm University, Faculty of Science, Department of Physics.
    Misra, Deepankar
    Stockholm University, Faculty of Science, Department of Physics.
    Reinhed, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt-Boecking, H.
    Schuch, Reinhold
    Stockholm University, Faculty of Science, Department of Physics.
    Schoeffler, M.
    Stochkel, K.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Angular scattering in fast ion-atom electron transfer collisions: projectile wave diffraction and Thomas mechanisms2010In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 43, no 18, p. 185209-Article in journal (Refereed)
    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.

  • 30.
    Gudmundsson, Magnus
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Fischer, D
    Misra, D
    Källberg, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Simonsson, Ansgar
    Stockholm University, Faculty of Science, Department of Physics.
    Støchkel, K
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, H. T.
    Orientation-dependent charge transfer cross section in 1.04MeV p-N2 collisionsManuscript (preprint) (Other academic)
  • 31.
    Haag, Nicole
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Holm, Anne I. S.
    Stockholm University, Faculty of Science, Department of Physics.
    Johansson, Henrik A. B.
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Brøndsted Nielsen, Steen
    Hvelplund, Preben
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Electron capture induced dissociation of doubly protonated pentapeptides: Dependence on molecular structure and charge separation2011In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 134, no 3, p. 035102-Article in journal (Refereed)
    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.

  • 32.
    Haag, Nicole
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Liu, Bo
    Brøndsted Nielsen, Steen
    Zettergren, Henning
    Hvelplund, Preben
    Manil, Bruno
    Huber, Bernd A.
    Johansson, Henrik A. B.
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Collisions with biomolecules embedded in smallwater clusters2009Conference paper (Refereed)
    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.

  • 33. Hansen, K.
    et al.
    Stockett, Mark H.
    Stockholm University, Faculty of Science, Department of Physics. Aarhus University, Denmark.
    Kaminska, Magdalena
    Stockholm University, Faculty of Science, Department of Physics. Jan Kochanowski University, Poland.
    Nascimento, Rodrigo F.
    Stockholm University, Faculty of Science, Department of Physics. Centro Federal de Educacao Tecnologica Celso Suckow da Fonseca, Brazil.
    Anderson, Emma K.
    Stockholm University, Faculty of Science, Department of Physics.
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Chartkunchand, Kiattichart C.
    Stockholm University, Faculty of Science, Department of Physics.
    Eklund, Gustav
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Spontaneous decay of small copper-cluster anions Cu-n(-) (n=3-6), on long time scales2017In: Physical Review A, ISSN 2469-9926, Vol. 95, no 2, article id 022511Article in journal (Refereed)
    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.

  • 34.
    Holm, Anne I. S.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Johansson, Henrik A. B.
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Dissociation and multiple ionization energies for five polycyclic aromatic hydrocarbon molecules2011In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 134, no 4, p. 044301-Article in journal (Refereed)
    Abstract [en]

    We have performed density functional theory calculations for a range of neutral, singly, and multiply charged polycyclic aromatic hydrocarbons (PAHs), and their fragmentation products for H-, H+-, C2H2-, and C2H2+-emissions. The adiabatic and vertical ionization energies follow linear dependencies as functions of charge state for all five intact PAHs (naphthalene, biphenylene, anthracene, pyrene, and coronene). First estimates of the total ionization and fragmentation cross sections in ion-PAH collisions display markedly different size dependencies for pericondensed and catacondensed PAH species, reflecting differences in their first ionization energies. The dissociation energies show that the PAHq+-molecules are thermodynamically stable for q <= 2 (naphthalene, biphenylene, and anthracene), q <= 3 (pyrene), and q <= 4 (coronene). PAHs in charge states above these limits may also survive experimental time scales due to the presence of reaction barriers as deduced from explorations of the potential energy surface regions for H+-emissions from all five PAHs and for C2H2+-emission from naphthalene - the smallest PAH.

  • 35.
    Holm, Anne I. S.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Johansson, Henrik A. B.
    Stockholm University, Faculty of Science, Department of Physics.
    Seitz, Fabian
    Stockholm University, Faculty of Science, Department of Physics.
    Rosen, Stefan
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Lawicki, A.
    Rangama, J.
    Rousseau, P.
    Capron, M.
    Maisonny, R.
    Adoui, L.
    Mery, A.
    Manil, B.
    Huber, B. A.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Ions Colliding with Cold Polycyclic Aromatic Hydrocarbon Clusters2010In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 105, no 21, p. 213401-Article in journal (Refereed)
    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+).

  • 36.
    Johansson, Henrik A. B.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Holm, Anne I. S.
    Stockholm University, Faculty of Science, Department of Physics.
    Haag, Nicole
    Stockholm University, Faculty of Science, Department of Physics.
    Brøndsted Nielsen, S.
    Wyer, J. A.
    Kirketerp, M.-B. S.
    Støchkel, K.
    Hvelplund, P.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Unimolecular dissociation of anthracene and acridine cations: The importance of isomerization barriers for the C2H2 loss and HCN loss channels2011In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 135, p. 084304-Article in journal (Refereed)
    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.

  • 37.
    Johansson, Henrik A. B.
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Holm, Anne I. S.
    Stockholm University, Faculty of Science, Department of Physics.
    Seitz, Fabian
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    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
    Stockholm University, Faculty of Science, Department of Physics.
    Ionization and fragmentation of polycyclic aromatic hydrocarbon clusters in collisions with keV ions2011In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 84, no 4, p. 043201-Article in journal (Refereed)
    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.

  • 38.
    Kamińska, Magdalena
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Jan Kochanowski University, Poland.
    Davis, V. T.
    Hole, Odd Magnar
    Stockholm University, Faculty of Science, Department of Physics.
    Nascimento, Rodrigo F.
    Stockholm University, Faculty of Science, Department of Physics. Centro Federal de Educação Tecnológica Celso Suckow da Fonseca, Brazil.
    Chartkunchand, Kiattichart C.
    Stockholm University, Faculty of Science, Department of Physics. University of Nevada, USA.
    Blom, Mikael
    Stockholm University, Faculty of Science, Department of Physics.
    Björkhage, Mikael
    Stockholm University, Faculty of Science, Department of Physics.
    Källberg, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Löfgren, Patrik
    Stockholm University, Faculty of Science, Department of Physics.
    Reinhed, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Rosén, Stefan
    Stockholm University, Faculty of Science, Department of Physics.
    Simonsson, Ansgar
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Mannervik, Sven
    Stockholm University, Faculty of Science, Department of Physics.
    Neill, P. A.
    Thompson, J. S.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Hanstorp, D.
    Lifetime of the bound excited level in Ni-2016In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 93, no 1, article id 012512Article in journal (Refereed)
    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.

  • 39.
    Kulyk, Kostiantyn
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Rebrov, Oleksii
    Stockholm University, Faculty of Science, Department of Physics.
    Stockett, Mark H.
    Stockholm University, Faculty of Science, Department of Physics.
    Alexander, John D.
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    High-energy collisions of protonated enantiopure amino acids with a chiral target gas2015In: International Journal of Mass Spectrometry, ISSN 1387-3806, E-ISSN 1873-2798, Vol. 388, p. 59-64Article in journal (Refereed)
    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.

  • 40.
    Kulyk, Kostiantyn
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Wolf, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics. Universität Innsbruck, Austria.
    Giacomozzi, Linda
    Stockholm University, Faculty of Science, Department of Physics.
    Vegvari, Akos
    Kovalenko, Oleksandr
    de Ruette, Nathalie
    Stockholm University, Faculty of Science, Department of Physics.
    Wendt, Ola
    Zubarev, Roman
    Schmidt, T. Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Collision Induced Dissociation of the retinal chromophore Schiff base from sub-eV to keV collision energiesIn: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215Article in journal (Refereed)
    Abstract [en]

    The gas-phase fragmentation of the protonated n-butylamine Schiff base of all-trans-retinal (NB-RPSB) was measured in low- and high-energy collisional activation modes. The protonated n-butyl β-ionone Schiff base (NB-BISB) peak at m/z = 248, known to be formed as a result of a complex gas-phase rearrangement reaction, has been reported to dominate in mass spectra of NB-RPSB after photo- and collisionally activated fragmentation processes. Earlier reported high-energy collision (50 keV) mass spectra have shown a broad distribution of the fragments with the peak at m/z = 248 present but not dominating. We observed the formation of a peak at m/z = 248 only in collisional activation of NB-RPSB parent ion below a few eV, which shows that the rearrangement process is extremely efficient and happens in a very narrow energy range. On the other hand, our high-energy collision induced dissociation experiments yielded fragmentation patterns, which are fully accounted for simple bond cleavages of the NB-RPSB molecular backbone. We do not observe any peak corresponding to the formation of NB-BISB in the 10 eV – 1 keV collision energy range. This leaves the question open why this fragment reappears in the mass spectra at much higher energies.

  • 41. Lawicki, A.
    et al.
    Holm, Anne I. S.
    Stockholm University, Faculty of Science, Department of Physics.
    Rousseau, P.
    Capron, M.
    Maisonny, R.
    Maclot, S.
    Seitz, Fabian
    Stockholm University, Faculty of Science, Department of Physics.
    Johansson, Henrik A. B.
    Stockholm University, Faculty of Science, Department of Physics.
    Rosén, Stefan
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Manil, B.
    Adoui, L.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Huber, B. A.
    Multiple ionization and fragmentation of isolated pyrene and coronene molecules in collision with ions2011In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 83, no 2, p. 022704-Article in journal (Refereed)
    Abstract [en]

    The interaction of multiply charged ions (He2+, O3+, and Xe20+) with gas-phase pericondensed polycyclic aromatic hydrocarbon (PAH) molecules of coronene (C24H12) and pyrene (C16H10) is studied for low-velocity collisions (v <= 0.6 a.u.). The mass spectrometric analysis shows that singly and up to quadruply charged intact molecules are important reaction products. The relative experimental yields are compared with the results of a simple classical over-the-barrier model. For higher molecular charge states, the experimental yields decrease much more strongly than the model predictions due to the instabilities of the multiply charged PAH molecules. Even-odd oscillations with the number of carbon atoms, n, in the intensity distributions of the CnHx+ fragments indicate a linear chain structure of the fragments similar to those observed for ion-C60 collisions. The latter oscillations are known to be due to dissociation energy differences between even-and odd-n Cn-chain molecules. For PAH molecules, the average numbers of H atoms attached to the CnHx chains are larger for even-n reflecting acetylenic bond systems.

  • 42.
    Lindén, Fredrik
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Interaction and charge transfer between dielectric spheres: Exact and approximate analytical solutions2016In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 145, no 19, article id 194307Article in journal (Refereed)
    Abstract [en]

    We present exact analytical solutions for charge transfer reactions between two arbitrarily charged hard dielectric spheres. These solutions, and the corresponding exact ones for sphere-sphere interaction energies, include sums that describe polarization effects to infinite orders in the inverse of the distance between the sphere centers. In addition, we show that these exact solutions may be approximated by much simpler analytical expressions that are useful for many practical applications. This is exemplified through calculations of Langevin type cross sections for forming a compound system of two colliding spheres and through calculations of electron transfer cross sections. We find that it is important to account for dielectric properties and finite sphere sizes in such calculations, which for example may be useful for describing the evolution, growth, and dynamics of nanometer sized dielectric objects such as molecular clusters or dust grains in different environments including astrophysical ones.

  • 43. Liu, B.
    et al.
    Haag, Nicole
    Stockholm University, Faculty of Science, Department of Physics.
    Johansson, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Brondsted Nielsen, S.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Hvelplund, P.
    Manil, B.
    Huber, B. A.
    Electron capture induced dissociation of nucleotide anions in water nanodroplets2008In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 128, no 7, p. 075102-Article in journal (Refereed)
    Abstract [en]

    We have studied the outcome of collisions between the hydrated nucleotide anion adenosine 5′-monophosphate (AMP) and sodium. Electron capture leads to hydrogen loss as well as water evaporation regardless of the initial number m of water molecules attached to the parent ion (m ⩽ 16). The yield of dianions with microsecond lifetimes increases strongly with m, which is explained from dielectric screening of the two charges by the water nanodroplet. For comparison, collision induced dissociation results in water losses with no or very little damage of the AMP molecule itself.

  • 44.
    Misra, Deepankar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning Thordal
    Stockholm University, Faculty of Science, Department of Physics.
    Gudmundsson, Magnus
    Stockholm University, Faculty of Science, Department of Physics.
    Fischer, Daniel
    Max-Planck Institut, Heidelberg.
    Haag, Nicole
    Stockholm University, Faculty of Science, Department of Physics.
    Johansson, Henrik A B
    Stockholm University, Faculty of Science, Department of Physics.
    Källberg, Anders
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Najjari, B
    Max-Planck Institut, Heidelberg.
    Reinhed, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Schuch, Reinhold
    Stockholm University, Faculty of Science, Department of Physics.
    Schöffler, Marcus
    Frankfurt University.
    Simonsson, Ansgar
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Voitkiv, A B
    Max-Planck Institut, Heidelberg.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Two-Center Double-Capture Interference in Fast He2++H2 Collisions2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, no 15, p. 153201-Article in journal (Refereed)
    Abstract [en]

    We report the first observation of Young-type interference effects in a two-electron transfer process. These effects change strongly as the projectile velocity changes in fast (1.2 and 2.0 MeV) He^{2+}-H_2 collisions as manifested in strong variations of the double-electron capture rates with the H_2 orientation. This is consistent with fully quantum mechanical calculations, which ignore sequential electron transfer, and a simple projectile de Broglie wave picture assuming that two-electron transfer probabilities are higher in collisions where the projectile passes close to either one of the H_2 nuclei.

  • 45.
    Reinhed, Peter
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Orbán, Andrea
    Stockholm University, Faculty of Science, Department of Physics.
    Rosén, Stefan
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard
    Stockholm University, Faculty of Science, Department of Physics.
    Kashperka, Iryna
    Stockholm University, Faculty of Science, Department of Physics.
    Johansson, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Misra, Deepankar
    Stockholm University, Faculty of Science, Department of Physics.
    Fardi, Afshin
    Brännholm, Lars
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Björkhage, Mikael
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Cryogenic keV ion-beam storage in ConeTrap - a tool for ion-temperature control2010In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 621, no 1-3, p. 83-90Article in journal (Refereed)
    Abstract [en]

    We have tested the ion-storage capabilities of the compact triple-electrode electrostatic ion-beam trap, ConeTrap, down to cryogenic temperatures. The low-temperature operation of this electrostatic storage device is an important test for the double electrostatic ion-ring experiment, DESIREE, which is presently under construction at Stockholm University. In the present work we measured the pressure dependent storage lifetimes of 2.5 keV He+ and 2.8 keV Ar+ ion beams in ConeTrap at temperatures down to 28 K and pressures down to 1.3·10-10 mbar. The so far longest measured ion storage lifetime using this system is 21.5±3.8 s for Ar+ ions. The present combination of ConeTrap and the cryogenic experimental chamber was recently applied in the first black-body correction-free measurement of the lifetime of the metastable He- ion at 10 K [Phys. Rev. Lett. 103, 213002(2009)].

  • 46.
    Reinhed, Peter
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Orbán, Andrea
    Stockholm University, Faculty of Science, Department of Physics.
    Werner, Josefina
    Stockholm University, Faculty of Science, Department of Physics.
    Rosén, Stefan
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Kashperka, Iryna
    Stockholm University, Faculty of Science, Department of Physics.
    Johansson, Henrik A. B.
    Stockholm University, Faculty of Science, Department of Physics.
    Misra, Deepankar
    Stockholm University, Faculty of Science, Department of Physics.
    Brännholm, Lars
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Björkhage, Mikael
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Precision lifetime measurements of He- in a cryogenic electrostatic ion-beam trap2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 103, no 21, p. 213002-Article in journal (Refereed)
    Abstract [en]

    We have developed a small purely electrostatic ion-beam trap which may be operated in thermal equilibrium at precisely controlled temperatures down to 10 K. Thus, we avoid magnetic field induced mixing of quantum states and may effectively eliminate any influence from absorption of photons from black-body radiation. We report the first correction free measurements of the lifetimes of the 1s2s2p 4PoJ state of 4He- and the high precision result 359.0±0.7 μs for the J=5/2 level. The lifetimes for the J=3/2 and J=1/2 levels are determined to be 12.3±0.5 and 7.8±1.0 μs, respectively.

  • 47.
    Rosén, Stefan
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Reinhed, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Fischer, Daniel
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Liljeby, Leif
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Bagge, Lars
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Leontein, Sven
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Blom, Mikael
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Operating a triple stack microchannel plate-phosphor assembly for single particle counting in the 12-300 K temperature range2007In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 78, no 11, p. 113301-Article in journal (Refereed)
    Abstract [en]

    An assembly consisting of a stack of three microchannel plates (MCPs) and a phosphor screen anode has been operated over the temperature range from 300 to 12 K. We report on measurements at 6.4 kHz (using an alpha source) and with dark counts only (15 Hz). Without any particle source,  the MCP bias current decreased by a factor of 2.1×103 when the temperature was lowered from 300 to 12 K. Using the alpha source, and a photomultiplier tube (PMT) to monitor the phosphor screen anode, we first observed an increase in the decay time of the phosphor from 12 to 45 μs when the temperature was decreased from 300 to 100 K while the decay time then decreased and reached a value of 5 μs at 12 K. The pulse height distribution from the PMT was measured between300 and 12 K and shows a spectrum typical for a MCP phosphor setup at 300 K and 12 K but is strongly degraded for intermediate temperatures. We conclude that the present MCP-phosphor detector assembly is well suited for position-sensitive particle counting operation at temperatures down to at least 12 K even for count rates beyond 6 kHz. This result is crucial and an important part of ongoing developments of new instrumentation for investigations of, e.g., interactions involving complex molecular ions with internal quantum state control.

  • 48. Rousseau, P.
    et al.
    Lawicki, A.
    Holm, Anne I. S.
    Stockholm University, Faculty of Science, Department of Physics.
    Capron, M.
    Maisonny, R.
    Maclot, S.
    Lattouf, E.
    Johansson, Henrik A. B.
    Stockholm University, Faculty of Science, Department of Physics.
    Seitz, Fabian
    Stockholm University, Faculty of Science, Department of Physics.
    Mery, A.
    Rangama, J.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Rosen, S.
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Chesnel, J. -Y
    Domaracka, A.
    Manil, B.
    Adoui, L.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Huber, B. A.
    Low energy ions interacting with anthracene molecules and clusters2012In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 279, p. 140-143Article in journal (Refereed)
    Abstract [en]

    The interaction of slow ions (nu similar to 0.4 au.) with a small polycyclic aromatic hydrocarbon, namely anthracene (C14H10), is studied in the gas-phase either with the isolated molecule or with a pure cluster target. We discuss the ionization and fragmentation of the molecule with respect to the projectile charge state, i.e. for singly charged He+ ions and for multiply charged Xe20+. ions. For the isolated C14H10, single or multiple ionization of the molecule occurs under ion impact. The (multi) cation relative yields are compared with those obtained by other ionization methods (electron and fs-laser). The molecular dissociation occurs by loss of hydrogen and small hydrocarbon molecules, leading to the formation of CnHx cations. The interaction of Xe20+ with C14H10 clusters gives surprising results, i.e. the emission of hotter monomer compared to the interaction with He+.

  • 49. Rudy, Delaunay
    et al.
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Rousseau, Patrick
    Domaracka, Alicja
    Maclot, Sylvain
    Wang, Yang
    Stockett, Mark H.
    Stockholm University, Faculty of Science, Department of Physics.
    Chen, Tao
    Stockholm University, Faculty of Science, Department of Physics.
    Adoui, Lamri
    Manuel, Alcami
    Martin, Fernando
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Huber, Bernd A.
    Molecular growth inside polycyclic aromatic hydrocarbon clusters induced by ion collisions2015In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 6, no 9, p. 1536-1542Article in journal (Refereed)
    Abstract [en]

    The present work combines experimental and theoretical studies of the collision between keV ion projectiles and clusters of pyrene, one of the simplest polycyclic aromatic hydrocarbons (PAHs). Intracluster growth processes induced by ion collisions lead to the formation of a wide range of new molecules with masses larger than that of the pyrene molecule. The efficiency of these processes is found to strongly depend on the mass and velocity of the incoming projectile. Classical molecular dynamics simulations of the entire collision process-from the ion impact (nuclear scattering) to the formation of new molecular species-reproduce the essential features of the measured molecular growth process and also yield estimates of the related absolute cross sections. More elaborate density functional tight binding calculations yield the same growth products as the classical simulations. The present results could be relevant to understand the physical chemistry of the PAH-rich upper atmosphere of Saturn’s moon Titan.

  • 50.
    Schmidt, Henning T.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Rosén, Stefan
    Stockholm University, Faculty of Science, Department of Physics.
    Reinhed, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Löfgren, Patrik
    Stockholm University, Faculty of Science, Department of Physics.
    Brännholm, Lars
    Stockholm University, Faculty of Science, Department of Physics.
    Blom, Mikael
    Stockholm University, Faculty of Science, Department of Physics.
    Björkhage, Mikael
    Stockholm University, Faculty of Science, Department of Physics.
    Bäckström, Erik
    Stockholm University, Faculty of Science, Department of Physics.
    Alexander, John D.
    Stockholm University, Faculty of Science, Department of Physics.
    Leontein, Sven
    Stockholm University, Faculty of Science, Department of Physics.
    Hanstorp, D.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Liljeby, Leif
    Stockholm University, Faculty of Science, Department of Physics.
    Källberg, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Simonsson, Ansgar
    Stockholm University, Faculty of Science, Department of Physics.
    Hellberg, Fredrik
    Stockholm University, Faculty of Science, Department of Physics.
    Mannervik, Sven
    Stockholm University, Faculty of Science, Department of Physics.
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Geppert, Wolf D.
    Stockholm University, Faculty of Science, Department of Physics.
    Rensfelt, Karl-Gunnar
    Stockholm University, Faculty of Science, Department of Physics.
    Danared, Håkan
    Stockholm University, Faculty of Science, Department of Physics.
    Paal, A.
    Stockholm University, Faculty of Science, Department of Physics.
    Masuda, Masaharu
    Stockholm University, Faculty of Science, Department of Physics.
    Hallden, Per
    Stockholm University, Faculty of Science, Department of Physics.
    Andler, Guillermo
    Stockholm University, Faculty of Science, Department of Physics.
    Stockett, Mark H.
    Stockholm University, Faculty of Science, Department of Physics.
    Chen, Tao
    Stockholm University, Faculty of Science, Department of Physics.
    Källersjö, Gunnar
    Stockholm University, Faculty of Science, Department of Physics.
    Weimer, Jan
    Stockholm University, Faculty of Science, Department of Physics.
    Hansen, K.
    Hartman, H.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    First storage of ion beams in the Double Electrostatic Ion-Ring Experiment: DESIREE2013In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 84, no 5, p. 055115-Article in journal (Refereed)
    Abstract [en]

    We report on the first storage of ion beams in the Double ElectroStatic Ion Ring ExpEriment, DESIREE, at Stockholm University. We have produced beams of atomic carbon anions and small carbon anion molecules (C-n(-), n = 1, 2, 3, 4) in a sputter ion source. The ion beams were accelerated to 10 keV kinetic energy and stored in an electrostatic ion storage ring enclosed in a vacuum chamber at 13 K. For 10 keV C-2(-) molecular anions we measure the residual-gas limited beam storage lifetime to be 448 s +/- 18 s with two independent detector systems. Using the measured storage lifetimes we estimate that the residual gas pressure is in the 10(-14) mbar range. When high current ion beams are injected, the number of stored particles does not follow a single exponential decay law as would be expected for stored particles lost solely due to electron detachment in collision with the residual-gas. Instead, we observe a faster initial decay rate, which we ascribe to the effect of the space charge of the ion beam on the storage capacity.

12 1 - 50 of 76
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