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  • 51.
    Stockett, Mark H.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Adoui, L.
    Alexander, J. D.
    Bērziņš,, U.
    Chen, Tao
    Stockholm University, Faculty of Science, Department of Physics.
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Haag, N.
    Huber, B. A.
    Hvelplund, P.
    Johansson, A.
    Stockholm University, Faculty of Science, Department of Physics.
    Johansson, Henrik A. B.
    Stockholm University, Faculty of Science, Department of Physics.
    Kulyk, Kostiantyn
    Stockholm University, Faculty of Science, Department of Physics.
    Rosén, S.
    Rousseau, P.
    Støchkel, K.
    Schmidt, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Nonstatistical fragmentation of large molecules2014In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 89, no 3, article id 032701Article in journal (Refereed)
    Abstract [en]

    We present experimental evidence for the dominance of prompt single-atom knockout in fragmenting collisions between large polycyclic aromatic hydrocarbon cations and He atoms at center-of-mass energies close to 100 eV. Such nonstatistical processes are shown to give highly reactive fragments. We argue that nonstatistical fragmentation is dominant for any sufficiently large molecular system under similar conditions.

  • 52.
    Stockett, Mark H.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Björkhage, Mikael
    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.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Storage time dependent photodissociation action spectroscopy of polycyclic aromatic hydrocarbon cations in the cryogenic electrostatic storage ring DESIREE2019In: Faraday discussions (Online), ISSN 1359-6640, E-ISSN 1364-5498, Vol. 217, p. 126-137Article in journal (Refereed)
    Abstract [en]

    The multi-photon photodissociation action spectrum of the coronene cation (C24H12+) has been measured in the cryogenic electrostatic storage ring DESIREE (Double ElectroStatic Ion Ring ExpEriment) as a function of storage time. These measurements reveal not only the intrinsic absorption profile of isolated coronene cations, but also the rate at which hot-band absorptions are quenched by radiative cooling. Just after injection, the action spectrum is severely reddened by hot-band absorptions. These hot bands fade with a time constant of 200 ms, which is consistent with radiative cooling via infrared emission from vibrational transitions. A comparison of the present results to those obtained in cryogenic ion trap experiments is discussed at length.

  • 53.
    Stockett, Mark H.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Alexander, John D.
    Stockholm University, Faculty of Science, Department of Physics.
    Berzins, U.
    Chen, Tao
    Stockholm University, Faculty of Science, Department of Physics.
    Farid, K.
    Stockholm University, Faculty of Science, Department of Physics.
    Johansson, A.
    Stockholm University, Faculty of Science, Department of Physics.
    Kulyk, Kostiantyn
    Stockholm University, Faculty of Science, Department of Physics.
    Rousseau, P.
    Stochkel, K.
    Adoui, L.
    Hvelptund, P.
    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.
    Fragmentation of anthracene C14H10, acridine C13H9N and phenazine C12H8N2 ions in collisions with atoms2014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 40, p. 21980-21987Article in journal (Refereed)
    Abstract [en]

    We report experimental total, absolute, fragmentation cross sections for anthracene C14H10, acridine C13H9N, and phenazine C12H8N2 ions colliding with He at center-of-mass energies close to 100 eV. In addition, we report results for the same ions colliding with Ne, Ar, and Xe at higher energies. The total fragmentation cross sections for these three ions are the same within error bars for a given target. The measured fragment mass distributions reveal significant contributions from both delayed (>> 10(-12) s) statistical fragmentation processes as well as non-statistical, prompt (similar to 10(-15) s), single atom knockout processes. The latter dominate and are often followed by secondary statistical fragmentation. Classical Molecular Dynamics (MD) simulations yield separate cross sections for prompt and delayed fragmentation which are consistent with the experimental results. The intensity of the single C/N-loss peak, the signature of non-statistical fragmentation, decreases with the number of N atoms in the parent ion. The fragment intensity distributions for losses of more than one C or N atom are rather similar for C14H10 and C13H9N but differ strongly for C12H8N2 where weak C-N bonds often remain in the fragments after the first fragmentation step. This greatly increases their probability to fragment further. Distributions of internal energy remaining in the fragments after knockout are obtained from the MD simulations.

  • 54.
    Stockett, Mark H.
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Aarhus University, Denmark.
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Chen, Tao
    Stockholm University, Faculty of Science, Department of Physics.
    de Ruette, Nathalie
    Stockholm University, Faculty of Science, Department of Physics.
    Giacomozzi, Linda
    Stockholm University, Faculty of Science, Department of Physics.
    Wolf, Michael
    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.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Threshold Energies for Single-Carbon Knockout from Polycyclic Aromatic Hydrocarbons2015In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 6, no 22, p. 4504-4509Article in journal (Refereed)
    Abstract [en]

    We have measured absolute cross sections for ultrafast (femtosecond) single-carbon knockout from polycyclic aromatic hydrocarbon (PAR) cations as functions of He-PAR center-of-mass collision energy in the 10-200 eV range. Classical molecular dynamics (MD) simulations cover this range and extend up to 105 eV. The shapes of the knockout cross sections are well-described by a simple analytical expression yielding experimental and MD threshold energies of E-th(Exp) = 32.5 +/- 0.4 eV and E-th(MD) = 41.0 +/- 0.3 eV, respectively. These are the first measurements of knockout threshold energies for molecules isolated in vacuo. We further deduce semiempirical (SE) and MD displacement energies, i.e., the energy transfers to the PAH molecules at the threshold energies for knockout, of T-disp(SE) = 23.3 +/- 0.3 eV and T-disp(MD) = 27.0 +/- 0.3 eV. The semiempirical results compare favorably with measured displacement energies for graphene (T-disp = 23.6 eV).

  • 55.
    Stockett, Mark H.
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Aarhus University, Denmark.
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    de Ruette, Nathalie
    Stockholm University, Faculty of Science, Department of Physics.
    Giacomozzi, Linda
    Stockholm University, Faculty of Science, Department of Physics.
    Chen, Tao
    Stockholm University, Faculty of Science, Department of Physics.
    Rousseau, P.
    Maclot, S.
    Chesnel, J. -Y.
    Adoui, L.
    Huber, B. A.
    Berzins, U.
    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.
    Isomer effects in fragmentation of Polycyclic Aromatic Hydrocarbons2015In: International Journal of Mass Spectrometry, ISSN 1387-3806, E-ISSN 1873-2798, Vol. 392, p. 58-62Article in journal (Refereed)
    Abstract [en]

    We have observed significant differences in the fragmentation patterns of isomeric Polycyclic Aromatic Hydrocarbon (PAH) cations following collisions with helium atoms at center-of-mass energies around 100 eV. This is in contrast to the situation at other collision energies or in photo-absorption experiments where isomeric effects are very weak and where the lowest-energy dissociation channels (H- and C2H2-loss) domihate in statistical fragmentation processes. In the 100 eV range, non-statistical fragmentation also competes and is uniquely linked to losses of single carbon atoms (CHx-losses). We find that such CHx-losses are correlated with the ionic ground state energy within a given group of isomers. We present results for three C16H10+, four C18H12+ and five C20H12+ isomers colliding with He.

  • 56.
    Stockett, Mark H.
    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.
    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.
    The threshold displacement energy of buckminsterfullerene C-60 and formation of the endohedral defect fullerene He@C-592018In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 139, p. 906-912Article in journal (Refereed)
    Abstract [en]

    We have measured the threshold center-of-mass kinetic energy for knocking out a single carbon atom from C-60(-) in collisions with He. Combining this experimental result with classical molecular dynamics simulations, we determine a semi-empirical value of 24.1+0.5 eV for the threshold displacement energy, the energy needed to remove a single carbon atom from the C-60 cage. We report the first observation of an endohedral complex with an odd number of carbon atoms, He@C-59(-), and discuss its formation and decay mechanisms.

  • 57.
    Thomas, Richard D.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    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.
    Bäckstrom, Erik
    Stockholm University, Faculty of Science, Department of Physics.
    Danared, Håkan
    Stockholm University, Faculty of Science, Department of Physics.
    Das, Susanta
    Stockholm University, Faculty of Science, Department of Physics.
    Haag, Nicole
    Stockholm University, Faculty of Science, Department of Physics.
    Halldén, Per
    Stockholm University, Faculty of Science, Department of Physics.
    Hellberg, Fredrik
    Stockholm University, Faculty of Science, Department of Physics.
    Holm, Anne I. S.
    Stockholm University, Faculty of Science, Department of Physics.
    Johansson, H. A. B.
    Stockholm University, Faculty of Science, Department of Physics.
    Källberg, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Källersjö, Gunnar
    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.
    Malm, Bo
    Stockholm University, Faculty of Science, Department of Physics.
    Mannervik, Sven
    Stockholm University, Faculty of Science, Department of Physics.
    Masuda, Masaharu
    Stockholm University, Faculty of Science, Department of Physics.
    Misra, Deepankar
    Stockholm University, Faculty of Science, Department of Physics.
    Orban, A.
    Stockholm University, Faculty of Science, Department of Physics.
    Paál, 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.
    Schmidt, K.
    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.
    Weimer, Jan
    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.
    The double electrostatic ion ring experiment: A unique cryogenic electrostatic storage ring for merged ion-beams studies2011In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 82, no 6, p. 065112-Article in journal (Refereed)
    Abstract [en]

    We describe the design of a novel type of storage device currently under construction at Stockholm University, Sweden, using purely electrostatic focussing and deflection elements, in which ion beams of opposite charges are confined under extreme high vacuum cryogenic conditions in separate rings and merged over a common straight section. The construction of this double electrostatic ion ring experiment uniquely allows for studies of interactions between cations and anions at low and well-defined internal temperatures and centre-of-mass collision energies down to about 10 K and 10 meV, respectively. Position sensitive multi-hit detector systems have been extensively tested and proven to work in cryogenic environments and these will be used to measure correlations between reaction products in, for example, electron-transfer processes. The technical advantages of using purely electrostatic ion storage devices over magnetic ones are many, but the most relevant are: electrostatic elements which are more compact and easier to construct; remanent fields, hysteresis, and eddy-currents, which are of concern in magnetic devices, are no longer relevant; and electrical fields required to control the orbit of the ions are not only much easier to create and control than the corresponding magnetic fields, they also set no upper mass limit on the ions that can be stored. These technical differences are a boon to new areas of fundamental experimental research, not only in atomic and molecular physics but also in the boundaries of these fields with chemistry and biology. For examples, studies of interactions with internally cold molecular ions will be particular useful for applications in astrophysics, while studies of solvated ionic clusters will be of relevance to aeronomy and biology.

  • 58.
    Thomas, Richard D.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Rosén, Sara
    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.
    Kaminska, Magdalena
    Stockholm University, Faculty of Science, Department of Physics.
    Nascimento, Rodrigo
    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.
    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.
    DESIREE: Physics with cold stored ion beams2015In: DR2013: Ninth international conference on dissociative recombination: theory, experiment, and applications, 2015, Vol. 84, article id 01004Conference paper (Refereed)
    Abstract [en]

    Here we will briefly describe the commissioning of the Double ElectroStatic Ion Ring ExpEriment (DESIREE) facility at Stockholm University, Sweden. This device uses purely electrostatic focussing and deflection elements and allows ion beams of opposite charge to be confined under extreme high vacuum and cryogenic conditions in separate rings and then merged over a common straight section. This apparatus allows for studies of interactions between cations and anions at very low and well-defined centre-of-mass energies (down to a few meV) and at very low internal temperatures (down to a few K).

  • 59.
    Wolf, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Giacomozzi, Linda
    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.
    Stockett, H. Mark
    Stockholm University, Faculty of Science, Department of Physics. Aarhus University, Denmark.
    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.
    Hydrogenated pyrene: Statistical single-carbon loss below the knockout threshold2016In: European Physical Journal D: Atomic, Molecular and Optical Physics, ISSN 1434-6060, E-ISSN 1434-6079, Vol. 70, no 4, article id 85Article in journal (Refereed)
    Abstract [en]

    An ongoing discussion revolves around the question of what effect hydrogenation has oncarbon backbone fragmentation in polycyclic aromatic hydrocarbons (PAHs). In order to shedmore light on this issue, we have measured absolute single carbon loss cross sections incollisions between native or hydrogenated pyrene cations (C16H+ 10+m , m = 0, 6, 16) and He as functions of center-of-massenergies down to 20 eV. Classical molecular dynamics (MD) simulations give further insightinto energy transfer processes and also yield m-dependent threshold energies for prompt(femtoseconds) carbon knockout. Such fast, non-statistical fragmentation processesdominate CH x -loss for native pyrene (m = 0), while much slowerstatistical fragmentation processes contribute significantly to single-carbon loss for thehydrogenated molecules (m =6 and m =16). The latter is shown by measurements of large CH x -loss crosssections far below the MD knockout thresholds for C16H+ 16 and C16H+ 26.

  • 60.
    Wolf, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Kiefer, H. V.
    Langeland, J.
    Andersen, L. H.
    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.
    Stockett, M. H.
    PHOTO-STABILITY OF SUPER-HYDROGENATED PAHs DETERMINED BY ACTION SPECTROSCOPY EXPERIMENTS2016In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 832, no 1, article id 24Article in journal (Refereed)
    Abstract [en]

    We have investigated the photo-stability of pristine and super-hydrogenated pyrene cations (C16H10+m+, m = 0, 6, or 16) by means of gas-phase action spectroscopy. Optical absorption spectra and photoinduced dissociation mass spectra are presented. By measuring the yield of mass-selected photo-fragment ions as a function of laser pulse intensity, the number of photons (and hence the energy) needed for fragmentation of the carbon backbone was determined. Backbone fragmentation of pristine pyrene ions (C16H10+) requires absorption of three photons of energy just below 3 eV, whereas super-hydrogenated hexahydropyrene (C16H16+) must absorb two such photons and fully hydrogenated hexadecahydropyrene (C16H26+) only a single photon. These results are consistent with previously reported dissociation energies for these ions. Our experiments clearly demonstrate that the increased heat capacity from the additional hydrogen atoms does not compensate for the weakening of the carbon backbone when pyrene is hydrogenated. In photodissociation regions, super-hydrogenated Polycyclic Aromatic Hydrocarbons (PAHs) have been proposed to serve as catalysts for H-2 formation. Our results indicate that carbon backbone fragmentation may be a serious competitor to H-2 formation at least for small hydrogenated PAHs like pyrene.

  • 61. Wyer, Jean Ann
    et al.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Haag, Nicole
    Stockholm University, Faculty of Science, Department of Physics.
    Huber, Bernd A.
    Hvelplund, Preben
    Johansson, Henrik A. B.
    Stockholm University, Faculty of Science, Department of Physics.
    Maisonny, Remy
    Bröndsted Nielsen, Steen
    Rangama, Jimmy
    Rousseau, Patrick
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    On the hydrogen loss from protonated nucleobases after electronic excitation or collisional electron capture2009In: European journal of mass spectrometry, ISSN 1469-0667, E-ISSN 1751-6838, Vol. 15, p. 681-688Article in journal (Refereed)
    Abstract [en]

    In this work, we have subjected protonated nucleobases MH+ (M = guanine, adenine, thymine, uracil and cytosine) to a range of experiments that involve high-energy (50 keV) collision induced dissociation and electron capture induced dissociation. In the latter case, both neutralisation reionisation and charge reversal were done. For the collision induced dissociation experiments, the ions interacted with O2. In neutral reionisation, caesium atoms were used as the target gas and the protonated nucleobases captured electrons to give neutrals. These were reionised to cations a microsecond later in collisions with O2. In choosing Cs as the target gas, we have assured that the first electron transfer process is favourable (by about 0.1–0.8 eV depending on the base). In the case of protonated adenine, charge reversal experiments (two Cs collisions) were also carried out, with the results corroborating those from the neutralisation reionisation experiments. We find that while collisional excitation of protonated nucleobases in O2 may lead to hydrogen loss with limited probabilities, this channel becomes dominant for electron capture events. Indeed, when sampling reionised neutrals on a microsecond timescale, we see that the ratio between MH+ and M+ is 0.2–0.4 when one electron is captured from Cs. There are differences in these ratios between the bases but no obvious correlation with recombination energies was found.

  • 62.
    Zettergren, Henning
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Adoui, Lamri
    Bernigaud, Virgile
    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
    Johansson, Henrik A. B.
    Stockholm University, Faculty of Science, Department of Physics.
    Kadhane, Umesh
    Larsen, Mikkel Kofoed
    Liu, Bo
    Manil, Bruno
    Bröndsted Nielsen, Steen
    Panja, Subhasis
    Rangama, Jimmy
    Reinhed, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Stöchkel, Kristian
    Electron-Capture-Induced Dissociation of Microsolvated Di- and > Tripeptide Monocations: Elucidation of Fragmentation Channels from > Measurements of Negative Ions2009In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 10, no 9-10, p. 1619-1623Article in journal (Refereed)
    Abstract [en]

    The branching ratio between ammonia loss and NCα bond cleavage of singly charged microsolvated peptides after electron capture from cesium depends on the solvent molecule attached. Density functional calculations reveal that for [GA+H]+(CE) (G=glycine, A=alanine, CE=crown ether), the singly occupied molecular orbital of the neutral radical is located mainly on the amide group (see picture).

    The results from an experimental study of bare and microsolvated peptide monocations in high-energy collisions with cesium vapor are reported. Neutral radicals form after electron capture from cesium, which decay by H loss, NH3 loss, or NCα bond cleavage into characteristic z. and c fragments. The neutral fragments are converted into negatively charged species in a second collision with cesium and are identified by means of mass spectrometry. For protonated GA (G=glycine, A=alanine), the branching ratio between NH3 loss and NCα bond cleavage is found to strongly depend on the molecule attached (H2O, CH3CN, CH3OH, and 18-crown-6 ether (CE)). Addition of H2O and CH3OH increases this ratio whereas CH3CN and CE decrease it. For protonated AAA ([AAA+H]+), a similar effect is observed with methanol, while the ratio between the z1 and z2 fragment peaks remains unchanged for the bare and microsolvated species. Density functional theory calculations reveal that in the case of [GA+H]+(CE), the singly occupied molecular orbital is located mainly on the amide group in accordance with the experimental results.

  • 63.
    Zettergren, Henning
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Johansson, H. A. B.
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Jensen, J.
    Hvelplund, P.
    Tomita, S.
    Wang, Y.
    Martin, F.
    Alcami, M.
    Manil, B.
    Maunoury, L.
    Huber, B. A.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Magic and hot giant fullerenes formed inside ion irradiated weakly bound C-60 clusters2010In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 133, no 10, p. 104301-Article in journal (Refereed)
    Abstract [en]

    We find that the most stable fullerene isomers, C-70-C-94, form efficiently in close-to central collisions between keV atomic ions and weakly bound clusters of more than 15 C-60-molecules. We observe extraordinarily high yields of C-70 and marked preferences for C-78 and C-84. Larger even-size carbon molecules, C-96-C-180, follow a smooth log-normal (statistical) intensity distribution. Measurements of kinetic energies indicate that C-70-C-94 mainly are formed by coalescence reactions between small carbon molecules and Coo, while C-n with n >= 96 are due to self-assembly (of small molecules) and shrinking hot giant fullerenes.

  • 64.
    Zettergren, Henning
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Reinhed, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Støchkel, K
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Jensen, J
    Tomita, S
    B. Nielsen, S
    Hvelplund, P
    Manil, B
    Rangama, J
    Huber, B.A
    Fragmentation and ionization of C70 and C60 by slow ions of intermediate charge2006In: European Physical Journal D: Atomic, Molecular and Optical Physics, ISSN 1434-6060, E-ISSN 1434-6079, The European physical journal D Atomic, molecular and optical physics, Vol. 38, no 2, p. 299-306Article in journal (Refereed)
    Abstract [en]

      

     

     

     

     

     

        

     

     

     

     

     

     

     

      

     

    We have measured total and coincident (with outgoing charge-state analyzed projectiles) ionization

    and fragmentation spectra of C

     

    60 and C70 following collisions with Xe4+ and Kr4+ at v = 0.

    06 a.u.

    Intact positive fullerene ions in charge states up to five (C

     

    5+

    60

     

    and C

    5+

    70

     

    ) are produced with both projectiles

    and for Kr

     

    4++C70 collisions we even observe a small C

    6+

    70

     

    peak. The C

    3+

    60

     

    /702m (m

    = 1–7) intensity distributions

    are predominantly associated with the stabilization of three electrons on the projectile (

     

    s

    = 3) and

    are significantly different for Xe

     

    4+- and Kr4+

    -projectiles. On the other hand, we find remarkable similarities

    in the C

     

    +

    3

     

    -C

    +

    11

     

    multi-fragmentation pattern regardless of projectile species (mass) although they are

    associated with closer encounters in which the projectile is fully neutralized (

     

    s

    = 4). Simple Monte Carlo

    calculations of nuclear and electronic loss processes show that both these contributions are very similar

    in glancing Xe

     

    4++C60 and Kr4++C60

    collisions, suggesting that frontal (and more violent) collisions are

    strongly suppressed under the present experimental conditions. Nevertheless it is surprising that the more

    distant collisions (

     

    s = 3) are projectile mass dependent, while the closer collisions (s

    = 4) are not. This

    indicates that this simple approach (although it reproduces more advanced quantum mechanical calculations

    for slow collisions with

     

    singly

    charged atomic ions rather well) is not valid for a comprehensive

    description of the energy transfer processes in the present collision systems involving projectiles of higher

    charge states.

  • 65.
    Zettergren, Henning
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Rousseau, P.
    Wang, Y.
    Seitz, Fabian
    Stockholm University, Faculty of Science, Department of Physics.
    Chen, Tao
    Stockholm University, Faculty of Science, Department of Physics.
    Gatchell, Michael
    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.
    Rangama, J.
    Chesnel, J. Y.
    Capron, M.
    Poully, J. C.
    Domaracka, A.
    Mery, A.
    Maclot, S.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Adoui, L.
    Alcami, M.
    Tielens, A. G. G. M.
    Martin, F.
    Huber, B. A.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Formations of Dumbbell C-118 and C-119 inside Clusters of C-60 Molecules by Collision with alpha Particles2013In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 110, no 18, article id 185501Article in journal (Refereed)
    Abstract [en]

    We report highly selective covalent bond modifications in collisions between keV alpha particles and van der Waals clusters of C-60 fullerenes. Surprisingly, C-119(+) and C-118(+) are the dominant molecular fusion products. We use molecular dynamics simulations to show that C-59(+) and C-58(+) ions-effectively produced in prompt knockout processes with He2+-react rapidly with C-60 to form dumbbell C-119(+) and C-118(+). Ion impact on molecular clusters in general is expected to lead to efficient secondary reactions of interest for astrophysics. These reactions are different from those induced by photons.

  • 66.
    Zettergren, Henning
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Rousseau, P.
    Wang, Y.
    Seitz, Fabian
    Stockholm University, Faculty of Science, Department of Physics.
    Chen, Tao
    Stockholm University, Faculty of Science, Department of Physics.
    Gatchell, Michael
    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.
    Rangama, J.
    Chesnel, J. Y.
    Capron, M.
    Poully, J. C.
    Domaracka, A.
    Méry, A.
    Maclot, S.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Adoui, L.
    Alcamí, M.
    Tielens, A. G. G. M.
    Martín, F.
    Huber, B. A.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Formation of dumb-bell C118 and C119 inside clusters of C60 -moleculesArticle in journal (Refereed)
    Abstract [en]

    We report highly selective covalent bond-modifications in collisions between keV alpha particles and van der Waals clusters of C60-fullerenes. Surprisingly, C119+ and C118+ are the dominant molecular fusion products. We use Molecular Dynamics simulations to show that C59+ and C58+ ions - effectively produced in prompt knock-out processes with He2+ - react rapidly with C60 to form dumb-bell C119+ and C118+ . Ion impact on molecular clusters in general is expected to lead to efficient secondary reactions of interest for astrophysics. These reactions are different from those induced by photons.

  • 67.
    Zettergren, Henning
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Rousseau, P.
    Wang, Y.
    Seitz, Fabian
    Stockholm University, Faculty of Science, Department of Physics.
    Chen, Tao
    Stockholm University, Faculty of Science, Department of Physics.
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Alexander, John D.
    Stockholm University, Faculty of Science, Department of Physics.
    Stockett, Mark H.
    Stockholm University, Faculty of Science, Department of Physics.
    Rangama, J.
    Chesnel, J. Y.
    Capron, M.
    Poully, J. C.
    Domaracka, A.
    Mery, A.
    Maclot, S.
    Vizcaino, V.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Adoui, L.
    Alcami, M.
    Tielens, A. G. G. M.
    Martin, F.
    Huber, B. A.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Bond formation in C-59(+)-C-60 collisions2014In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 488, p. 012028-Article in journal (Refereed)
    Abstract [en]

    In this work, we show that keV-ions are able to remove single carbon atoms from individual fullerenes in clusters of C-60 molecules. This very efficiently leads to the formation of exotic q dumbbell molecules through secondary C-59(+) - C-60 collisions within the fragmenting cluster. Such molecular fusion processes are inherently different from those induced by photons where only products with even numbers of carbon atoms are observed. Thus, ion collisions ignite unique and hitherto overlooked secondary reactions in small aggregates of matter. This relates to the question on how complex molecules may form in e.g. space.

12 51 - 67 of 67
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