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  • 1. Andersson, Patrik U.
    et al.
    Ojekull, Jenny
    Pettersson, Jan B. C.
    Markovic, Nikola
    Hellberg, Fredrik
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Ehlerding, Anneli
    Stockholm University, Faculty of Science, Department of Physics.
    Österdahl, Fabian
    Zhaunerchyk, Vitali
    Stockholm University, Faculty of Science, Department of Physics.
    Geppert, Wolf D.
    Stockholm University, Faculty of Science, Department of Physics.
    af Ugglas, Magnus
    Stockholm University, Faculty of Science, Department of Physics.
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Uggerud, Einar
    Danared, Hakan
    Kallberg, Anders
    Formation of Highly Rovibrationally Excited Ammonia from Dissociative Recombination of NH4+2010In: The journal of physical chemistry letters, ISSN 1948-7185, Vol. 1, no 17, p. 2519-2523Article in journal (Refereed)
    Abstract [en]

    The internal energy distribution of ammonia formed in the dissociative recombination (DR) of NH4+ with electrons has been studied by an imaging technique at the ion storage ring CRYRING. The DR process resulted in the formation of NH3 + H (0,90 +/- 0.01), with minor contributions from channels producing NH2 + H-2 (0.05 +/- 0.01) and NH2 + 2H (0.04 +/- 0.02). The formed NH3 molecules were highly internally excited, with a mean rovibrational energy of 3.3 +/- 0.4 eV, which corresponds to 70% of the energy released in the neutralization process. The internal energy distribution was semiquantitatively reproduced by ab initio direct dynamics simulations, and the calculations suggested that the NH3 molecules are highly vibrationally excited while rotational excitation is limited. The high internal,excitation and the translational energy of NH3 and H will influence their subsequent reactivity, an aspect that should be taken into account when developing detailed models of the interstellar medium and ammonia-containing plasmas.

  • 2. Bahati, E. M.
    et al.
    Fogle, M.
    Vane, C. R.
    Bannister, M. E.
    Thomas, R. D.
    Stockholm University, Faculty of Science, Department of Physics.
    Zhaunerchyk, Vitali
    Stockholm University, Faculty of Science, Department of Physics.
    Electron-impact dissociation of CD3+ and CH3+ ions producing CD2+, CH+ and C+ fragment ions2009In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 79, no 5, p. 52703-Article in journal (Refereed)
    Abstract [en]

    Using a crossed electron-ion beams method, we measured absolute cross sections for electron-impact dissociation of the CD3+ molecular ions producing CD2+ fragment ions and CH3+ ions yielding CH+ and C+ fragment ions over a collision energy range from a few eV up to 100 eV. The total experimental uncertainties are about 12% at the maximum of the curves of cross sections (peak of the cross section for the CH+ channel). The obtained results suggest important roles played by predissociation of bound states in the production of both the CH+ and C+ fragment ions. Good agreement is found with other results reported for the CH+ fragment, but some differences are found for the CD2+ and C+ fragments.

  • 3. Berrah, Nora
    et al.
    Fang, Li
    Murphy, Brendan
    Osipov, Timur
    Ueda, Kiyoshi
    Kukk, Edwin
    Feifel, Raimund
    van der Meulen, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Salén, Peter
    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.
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Richter, Robert
    Prince, Kevin C.
    Bozek, John D.
    Bostedt, Christoph
    Wada, Shin-ichi
    Piancastelli, Maria N.
    Tashiro, Motomichi
    Ehara, Masahiro
    Double-core-hole spectroscopy for chemical analysis with an intense X-ray femtosecond laser2011In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 108, no 41, p. 16912-16915Article in journal (Refereed)
    Abstract [en]

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

  • 4.
    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.

  • 5.
    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.

  • 6.
    Danielsson, Mathias
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Hamberg, Mathias
    Stockholm University, Faculty of Science, Department of Physics.
    Simonsson, Ansgar
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Paál, Andreas
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Geppert, Wolf
    Stockholm University, Faculty of Science, Department of Physics.
    Zhaunerchyk, Vitaly
    Stockholm University, Faculty of Science, Department of Physics.
    Ehlerding, Anneli
    Stockholm University, Faculty of Science, Department of Physics.
    Kaminska, Magdalena
    Stockholm University, Faculty of Science, Department of Physics.
    Hellberg, Fredrik
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard
    Stockholm University, Faculty of Science, Department of Physics.
    Österdal, Fabian
    af Ugglas, Magnus
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Källberg, Anders
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    The cross-section and branching fractions for dissociative recombination of the diacetylene cation C4D2+2008In: International Journal of Mass Spectrometry, ISSN 1387-3806, E-ISSN 1873-2798, Vol. 273, no 3, p. 111-116Article in journal (Refereed)
    Abstract [en]

    In this paper we report the results of a study on the dissociative recombination (DR) of the diacetylene cation, C4D2+, which has been carried out at the ion storage ring CRYRING in Stockholm, Sweden. The energy-dependent absolute DR cross-section as well as the branching fractions at 0 eV collision energy were measured. The DR cross-section was best fitted using the expression σ(E) = (7.5 ± 1.5) × 10−16 × E−(1.29±0.03) cm2 over the collision energy range 1–100 meV. The thermal rate coefficient was deduced from the cross-section to be α(T) = (1.10 ± 0.15) × 10−6 × (T/300)−(0.79±0.03) cm3/s. The reported branching fractions for C4D2+ agree with previous experiments on the DR of C4H2+ performed at the ASTRID storage ring in Aarhus, Denmark, and furthermore, indicate that the DR of C4D2+ possesses only two channels leading to the following products: C4D + D (75%) and C2D + C2D (25%).

  • 7. Fogle, M.
    et al.
    Bahati, E. M.
    Bannister, M. E.
    Deng, S. H. M.
    Vane, C. R.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Zhaunerchyk, Vitali
    Stockholm University, Faculty of Science, Department of Physics.
    Electron-impact dissociation of XH2+ (X = B, C, N, O, F): Absolute cross sections for production of XH+ and X+ fragment ions2010In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 82, no 4, p. 042720-Article in journal (Refereed)
    Abstract [en]

    Absolute cross sections for electron-impact dissociation of XH2+ (X = B, C, N, O, F) producing XH+ and X+ ion fragments were measured in the 3- to 100-eV range using a crossed-electron-ion beams technique. Dissociative excitation of BD2+ and CH2+ producing B+ and C+, respectively, show a propensity toward a two-body dissociation while the remaining species all tend to show a three-body dissociation dynamic. The BD+ and CH+ dissociative excitation channels show a large resonant-type contribution to the cross sections at similar to 10eV. For the X+ fragment ion production cross sections, a clear dependence on the threshold energy, as it relates to the rate of rise in the cross section above threshold, is observed.

  • 8. Fogle, M.
    et al.
    Bahati, E. M.
    Bannister, M. E.
    Deng, S. H. M.
    Vane, C. R.
    Thomas, Richard D.
    Zhaunerchyk, Vitali
    Stockholm University, Faculty of Science, Department of Physics.
    Electron-impact dissociative excitation and ionization of N(2)D(+)2011In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 84, no 3, p. 032714-Article in journal (Refereed)
    Abstract [en]

    Absolute cross sections for electron-impact dissociation of N(2)D(+) producing N(2)(+), ND(+), and N(+) ion fragments were measured in the 5- to 100-eV range using a crossed electron-ion beams technique. In the 5- to 20-eV region, in which dissociative excitation (DE) is the principal contributing mechanism, N(2)(+) production dominates. The N(2)(+) + D dissociation channel shows a large resonant-like structure in the DE cross section, as observed previously in electron impact dissociation of triatomic dihydride species [M. Fogle, E. M. Bahati, M. E. Bannister, S. H. M. Deng, C. R. Vane, R. D. Thomas, and V. Zhaunerchyk, Phys. Rev. A 82, 042720 (2010)]. In the dissociative ionization (DI) region, 20- to 100-eV, N(2)(+), ND(+), and N(+) ion fragment production are comparable. The observance of the ND(+) and N(+) ion fragments indicate breaking of the N-N bond along certain dissociation channels.

  • 9. Frasinski, L. J.
    et al.
    Zhaunerchyk, V.
    Mucke, M.
    Squibb, R. J.
    Siano, M.
    Eland, J. H. D.
    Linusson, Per
    Stockholm University, Faculty of Science, Department of Physics.
    van der Meulen, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Sahlén, Martin
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard
    Stockholm University, Faculty of Science, Department of Physics.
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Foucar, L.
    Ullrich, J.
    Motomura, K.
    Mondal, S.
    Ueda, K.
    Osipov, T.
    Fang, L.
    Murphy, B. F.
    Berrah, N.
    Bostedt, C.
    Bozek, J. D.
    Schorb, S.
    Messerschmidt, M.
    Glownia, J. M.
    Cryan, J. P.
    Coffee, R. N.
    Takahashi, O.
    Wada, S.
    Piancastelli, M. N.
    Richter, R.
    Prince, K. C.
    Feifel, R.
    Dynamics of Hollow Atom Formation in Intense X-Ray Pulses Probed by Partial Covariance Mapping2013In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 111, no 7, p. 073002-Article in journal (Refereed)
    Abstract [en]

    When exposed to ultraintense x-radiation sources such as free electron lasers (FELs) the innermost electronic shell can efficiently be emptied, creating a transient hollow atom or molecule. Understanding the femtosecond dynamics of such systems is fundamental to achieving atomic resolution in flash diffraction imaging of noncrystallized complex biological samples. We demonstrate the capacity of a correlation method called partial covariance mapping'' to probe the electron dynamics of neon atoms exposed to intense 8 fs pulses of 1062 eV photons. A complete picture of ionization processes competing in hollow atom formation and decay is visualized with unprecedented ease and the map reveals hitherto unobserved nonlinear sequences of photoionization and Auger events. The technique is particularly well suited to the high counting rate inherent in FEL experiments.

  • 10.
    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.

  • 11.
    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.

  • 12.
    Geng, Ting
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Galván, Ignacio F.
    Schalk, Oliver
    Stockholm University, Faculty of Science, Department of Physics.
    Lindh, Roland
    Hansson, Tony
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Time-resolved photoelectron spectroscopy studies on pyrazole and several methylated derivativesManuscript (preprint) (Other academic)
    Abstract [en]

    We present femtosecond time-resolved photoelectron spectra and ab initio studies on pyrazole andits methylated derivatives 1-, 3-, and 5-methylpyrazole. Excitation at 200 nm populates both the two lowest lying states, a 1ππ* state and a mixed 1πσ*/1π3s Rydberg state, from where three relaxation channels are observed: ring puckering, N-H bond cleavage, and ring opening via N-N bond breaking. The N-N bond breaking channel is the fastest process, occurring within one vibrational cycle of the Franc Condon active ring stretching mode. N-H bond cleavage is observed to be aminor channel, and occurs upon direct excitation to the mixed π3s/πσ* state. Finally, ring puckering occurs after a timescale of a few hundred fs because the molecules need time to find the gradient towards this conical intersection. However, this channel is accessed if the initially triggered processes are not successful. The quantum yields of the different channels were found to be very sensitive of the relative positioning of the excited states. In pyrazole and 5-methylpyrazole, N-Nbond cleavage dominates. In 1-, and 3-methylpyrazole, while the 1ππ* state drops in energy the dissociating 1πσ* valence state does not, and this leads to an increased barrier towards ring cleavage and a decreased the quantum yield for N-N bond cleavage. Upon excitation at 267 nm of 1- and 3-methylpyrazole, ring puckering is the only available pathway.

  • 13.
    Geng, Ting
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Schalk, Oliver
    Stockholm University, Faculty of Science, Department of Physics.
    Neville, Simon P.
    Hansson, Tony
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Dynamics in higher lying excited states: Valence to Rydberg transitions in the relaxation paths of pyrrole and methylated derivatives2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, no 14, article id 144307Article in journal (Refereed)
    Abstract [en]

    The involvement of intermediate Rydberg states in the relaxation dynamics of small organic molecules which, after excitation to the valence manifold, also return to the valence manifold is rarely observed. We report here that such a transiently populated Rydberg state may offer the possibility to modify the outcome of a photochemical reaction. In a time resolved photoelectron study on pyrrole and its methylated derivatives, N-methyl pyrrole and 2,5-dimethyl pyrrole, 6.2 eV photons (200 nm) are used to excite these molecules into a bright pi pi* state. In each case, a pi 3p-Rydberg state, either the B-1(pi 3p(y)) or the A(2)(pi 3p(z)) state, is populated within 20-50 fs after excitation. The wavepacket then proceeds to the lower lying A(2)(pi sigma*) state within a further 20 fs, at which point two competing reaction channels can be accessed: prompt N-H (N-CH3) bond cleavage or return to the ground state via a conical intersection accessed after ring puckering, the latter of which is predicted to require an additional 100-160 fs depending on the molecule.

  • 14.
    Geng, Ting
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Schalk, Oliver
    Stockholm University, Faculty of Science, Department of Physics.
    Neville, Simon P.
    Hansson, Tony
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Dynamics in higher lying excited states: Valence to Rydberg transitions in the relaxation paths of pyrrole and methylated derivativesManuscript (preprint) (Other academic)
    Abstract [en]

    The involvement of intermediate Rydberg states in the relaxation dynamics of small organic molecules which, after excitation to the valence manifold, also return to the valence manifold, is rarely observed. We report here that such a transiently populated Rydberg state may offer the possibility to modify the outcome of a photochemical reaction. In a time resolved photoelectron study on pyrrole and its methylated derivatives, N-methyl pyrrole and 2,5-dimethyl pyrrole, 6.2 eVphotons (200 nm) are used to excite these molecules into a bright ππ* state. In each case, a π3p-Rydberg state, either the B1(π3py) or the A2(π3pz) state, is populated within 20-50 fs after excitation. The wave packet then proceeds to the lower lyingA2(πσ*) state within a further 20 fs, at which point two competing reaction channels can be accessed: prompt NH (N-CH3) bond cleavage or ring puckering, the latter of which is predicted to require an additional 100 – 160 fs depending on the molecule.

  • 15.
    Geppert, W.D.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Hamberg, M.
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, R.D.
    Stockholm University, Faculty of Science, Department of Physics.
    Österdahl, F.
    Hellberg, F.
    Stockholm University, Faculty of Science, Department of Physics.
    Zhauernerchyk, V.
    Stockholm University, Faculty of Science, Department of Physics.
    Ehlerding, A.
    Stockholm University, Faculty of Science, Department of Physics.
    Millar, T.J.
    Roberts, H.
    Semaniak, J.
    af Ugglas, M.
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Källberg, Anders
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Simonsson, Ansgar
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Kaminska, M.
    Larsson, M.
    Stockholm University, Faculty of Science, Department of Physics.
    Dissociative recombination of protonated methanol2006In: Journal of the Chemical Society, Faraday Transactions, ISSN 0956-5000, E-ISSN 1364-5455, Vol. 133, p. 177-190Article in journal (Refereed)
  • 16.
    Hamberg, Mathias
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Kashperka, Iryna
    Stockholm University, Faculty of Science, Department of Physics.
    Danielsson, Mathias
    af Ugglas, Magnus
    Stockholm University, Faculty of Science, Department of Physics.
    Österdahl, Fabian
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Zhaunerchyk, Vitali
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Vigren, Erik
    Stockholm University, Faculty of Science, Department of Physics.
    Kaminska, Magdalena
    Jan Kochanowski University, Kielce, Poland.
    Källberg, Anders
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Simonsson, Ansgar
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Paál, András
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Geppert, Wolf
    Stockholm University, Faculty of Science, Department of Physics.
    Experimental studies on the dissociative recombination of H13CO+ with electrons at energies between 2 – 50 000 meVManuscript (preprint) (Other academic)
    Abstract [en]

    Determination of dissociative recombination processes of H13CO+ using merged ion-electron beam methods has been performed at the heavy storage ring CRYRING, Stockholm, Sweden. We have measured the branching fractions at ~0 eV as: CO+H 87±2%, OH+C 9±2% and O+CH 4±2%. The channels leading to CO+H have the following branching fractions between the accessible electronic states of CO(X1S+)+H 46±3%, CO(a3Pg)+H 20±1% and CO(a’3S+)+H 34±3% respectively. The reaction cross section was fitted between 1-300 meV and followed the expression σ = 1.2±0.25×10-16 E-1.32±0.02 cm2 and the corresponding thermal rate constant was determined to k(T) = 2.0±0.4×10−7(T/300)−0.82±0.02 cm3s−1. The cross sections between ~2-50 000 meV were investigated showing resonant structures between 3-15 eV.

  • 17.
    Hamberg, Mathias
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Uppsala University, Sweden.
    Kashperka, Iryna
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Roueff, Evelyne
    Zhaunerchyk, Vitali
    Stockholm University, Faculty of Science, Department of Physics. Uppsala University, Sweden.
    Danielsson, Mathias
    Stockholm University, Faculty of Science, Department of Physics.
    af Ugglas, Magnus
    Stockholm University, Faculty of Science, Department of Physics.
    Österdahl, Fabian
    Stockholm University, Faculty of Science, Department of Physics.
    Vigren, Erik
    Stockholm University, Faculty of Science, Department of Physics.
    Kaminska, Magdalena
    Källberg, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Simonsson, Ansgar
    Stockholm University, Faculty of Science, Department of Physics.
    Paál, Andras
    Stockholm University, Faculty of Science, Department of Physics.
    Gerin, Maryvonne
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Geppert, Wolf D.
    Stockholm University, Faculty of Science, Department of Physics.
    Experimental Studies of (HCO+)-C-13 Recombining with Electrons at Energies between 2-50 000 meV2014In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 118, no 31, p. 6034-6049Article in journal (Refereed)
    Abstract [en]

    An investigation into the dissociative recombination process for (HCO+)-C-13 using merged ion-electron beam methods has been performed at the heavy ion storage ring CRYRING, Stockholm, Sweden. We have measured the branching fractions of the different product channels at similar to 0 eV collision energy to be the following: CO + H 87 +/- 2%, OH + C 9 +/- 2%, and O + CH 4 +/- 2%. The formation of electronically excited CO in the dominant reaction channel has also been studied, and we report the following tentative branching fractions for the different CO product electronic states: CO(X (1)Sigma(+)) + H, 54 +/- 10%; CO(a (3)Pi) + H, 23 +/- 4%; and CO(a' (3)Sigma(+)) + H, 23 +/- 4%. The absolute cross section between similar to 2-50 000 meV was measured and showed resonance structures between 3 and 15 eV. The cross section was fitted in the energy range relevant to astrophysics, i.e., between 1 and 300 meV, and was found to follow the expression sigma = 1.3 +/- 0.3 X 10(-16) E-1.29 +/- 0.05 cm(2) and the corresponding thermal rate constant was determined to be k(T) = 2.0 +/- 0.4 X 10(-7)(T/300)(-0.79 +/- 0.05) cm(3) s(-1). Radioastronomical observations with the IRAM 30 m telescope of HCO+ toward the Red Rectangle yielded an upper column density limit of 4 X 10(11) cm(-2) of HCO+ at the 1 sigma level in that object, indicating that previous claims that the dissociative recombination of HCO+ plays an important role in the production of excited CO molecules emitting the observed Cameron bands in that object are not supported.

  • 18.
    Hamberg, Mathias
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Zhaunerchyk, Vitali
    Stockholm University, Faculty of Science, Department of Physics.
    Vigren, Erik
    Stockholm University, Faculty of Science, Department of Physics.
    Kaminska, Magdalena
    Jan Kochanowski University, Kielce, Poland.
    Kashperka, Iryna
    Stockholm University, Faculty of Science, Department of Physics.
    Zhang, Mingwu
    Institute of Modern Physics.
    Trippel, Sebastian
    Albert-Ludwigs-Universität Freiburg, Tyskland.
    Österdahl, Fabian
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    af Ugglas, Magnus
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Källberg, Anders
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Simonsson, Ansgar
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Paál, András
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Geppert, Wolf
    Stockholm University, Faculty of Science, Department of Physics.
    Experimental studies of the dissociative recombination for CD3CDOD+ and CH3CH2OH2+Manuscript (preprint) (Other academic)
    Abstract [en]

    Aims:  Determination of branching fractions, cross sections and thermal rate constants for the dissociative recombination of CD3CDOD+ and CH3CH2OH2+ at the low relative kinetic energies encountered in the interstellar medium.

    Methods: The experiments were carried out by merging an ion and electron beam at the heavy ion storage ring CRYRING, Stockholm, Sweden.

    Results: Break-up of the CCO structure into three heavy fragments is not found for either of the ions. Instead the CCO structure is retained in 23 ± 3% of the DR reactions of CD3CDOD+ and 7 ± 3% in the DR of CH3CH2OH2+, whereas rupture into two heavy fragments occurs in 77 ± 3% and 93 ± 3% of the DR events of the respective ions. The measured cross sections were fitted between 1-200 meV yielding the following thermal rate constants and cross-section dependencies on the relative kinetic energy: σ(Ecm[eV]) = 1.7 ± 0.3 × 1015(Ecm[eV])1.23±0.02 cm2 and k(T) = 1.9 ± 0.4 × 106(T/300)0.73±0.02 cm3s1 for CH3CH2OH2+  as well as k(T) = 1.1 ± 0.4 × 106(T/300)0.74±0.05 cm3s1 and σ(Ecm[eV]) = 9.2 ± 4 × 1016(Ecm[eV])1.24±0.05 cm2 for CD3CDOD+.

  • 19.
    Hamberg, Mathias
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Österdahl, Fabian
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Zhaunerchyk, Vitali
    Stockholm University, Faculty of Science, Department of Physics.
    Vigren, Erik
    Stockholm University, Faculty of Science, Department of Physics.
    Kaminska, Magdalena
    Jan Kochanowski University.
    af Ugglas, Magnus
    Stockholm University, Faculty of Science, Department of Physics.
    Källberg, Anders
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Simonsson, Ansgar
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Paál, András
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Larsson, Mats
    Geppert, Wolf D.
    Stockholm University, Faculty of Science, Department of Physics.
    Experimental studies of the dissociative recombination processes for the dimethyl ether ions CD3OCD2+ and (CD3)2OD+2010In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 514, p. A83-Article in journal (Refereed)
    Abstract [en]

    Aims: Determination of branching fractions, cross sections and thermal rate coefficients for the dissociative recombination of CD3OCD2+ (0-0.3 eV) and (CD3)2OD+ (0-0.2 eV) at the low relative kinetic energies encountered in the interstellar medium.

    Methods: The measurements were carried out using merged electron and ion beams at the CRYRING storage ring, Stockholm, Sweden.

    Results: For (CD3)2OD+ we have experimentally determined the branching fraction for ejection of a single hydrogen atom in the DR process to be maximally 7% whereas 49% of the reactions involve the break up of the COC chain into two heavy fragments and 44% ruptures both C-O bonds. The DR of CD3OCD2+ is dominated by fragmentation of the COC chain into two heavy fragments. The measured thermal rate constants and cross sections are k(T) =1.7 ± 0.5 × 106(T/300)0.77±0.01 cm3s−1,  σ= 1.2 ± 0.4 × 1015(Ecm[eV])1.27 ± 0.01 cm2 and k(T) = 1.7 ± 0.6 × 106(T/300)0.70±0.02 cm3s1,σ= 1.7 ± 0.6 × 1015(Ecm[eV])1.20±0.02 cm2 for CD3OCD2+ and (CD3)2OD+, respectively.

  • 20.
    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.

  • 21. Kreckel, Holger
    et al.
    Novotny, Oldrich
    Crabtree, Kyle N.
    Buhr, Henrik
    Petrignani, Annemieke
    Tom, Brian A.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Berg, Max H.
    Bing, Dennis
    Grieser, Manfred
    Krantz, Claude
    Lestinsky, Michael
    Mendes, Mario B.
    Nordhorn, Christian
    Repnow, Roland
    Stuetzel, Julia
    Wolf, Andreas
    McCall, Benjamin J.
    High-resolution storage-ring measurements of the dissociative recombination of H-3(+) using a supersonic expansion ion source2010In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 82, no 4, p. 042715-Article in journal (Refereed)
    Abstract [en]

    We have performed measurements of the dissociative electron recombination (DR) of H-3(+) at the ion storage ring TSR utilizing a supersonic expansion ion source. The ion source has been characterized by continuous wave cavity ring-down spectroscopy. We present high-resolution DR rate coefficients for different nuclear spin modifications of H-3(+) combined with precise fragment imaging studies of the internal excitation of the H-3(+) ions inside the storage ring. The measurements resolve changes in the energy dependence between the ortho-H-3(+) and para-H-3(+) rate coefficients at low center-of-mass collision energies. Analysis of the imaging data indicates that the stored H-3(+) ions may have higher rotational temperatures than previously assumed, most likely due to collisional heating during the extraction of the ions from the ion source. Simulations of the ion extraction shed light on possible origins of the heating process and how to avoid it in future experiments.

  • 22.
    Kulyk, Kostiantyn
    et al.
    Stockholm University, Faculty of Science, Department of Physics. SCA R&D Centre, Sweden.
    Rebrov, Oleksii
    Stockholm University, Faculty of Science, Department of Physics.
    Ryding, M.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Uggerud, E.
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Low-Energy Collisions of Protonated Enantiopure Amino Acids with Chiral Target Gases2017In: Journal of the American Society for Mass Spectrometry, ISSN 1044-0305, E-ISSN 1879-1123, Vol. 28, no 12, p. 2686-2691Article in journal (Refereed)
    Abstract [en]

    Here we report on the gas-phase interactions between protonated enantiopure amino acids (l- and d-enantiomers of Met, Phe, and Trp) and chiral target gases [(R)- and (S)-2-butanol, and (S)-1-phenylethanol] in 0.1-10.0 eV low-energy collisions. Two major processes are seen to occur over this collision energy regime, collision-induced dissociation and ion-molecule complex formation. Both processes were found to be independent of the stereo-chemical composition of the interacting ions and targets. These data shed light on the currently debated mechanisms of gas-phase chiral selectivity by demonstrating the inapplicability of the three-point model to these interactions, at least under single collision conditions.

  • 23.
    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.

  • 24.
    Larsson, Mats
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Salén, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    van der Meulen, Peter
    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.
    Feifel, R.
    Piancastelli, M. N.
    Fang, L.
    Murphy, B. F.
    Osipov, T.
    Berrah, N.
    Kukk, E.
    Ueda, K.
    Bozek, J. D.
    Bostedt, C.
    Wada, S.
    Richter, R.
    Feyer, V.
    Prince, K. C.
    Double core-hole formation in small molecules at the LCLS free electron laser2013In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 46, no 16, p. 164030-Article in journal (Refereed)
    Abstract [en]

    We have investigated nonlinear processes in small molecules by x-ray photoelectron spectroscopy using the Linac Coherent Light Source free electron laser, and by simulations. The main focus of the experiments was the formation of the two-site double core-hole (tsDCH) states in the molecules CO2, N2O and N-2. These experiments are described in detail and the results are compared with simulations of the photoelectron spectra. The double core-hole states, and in particular the tsDCH states, have been predicted to be highly sensitive to the chemical environment. The theory behind this chemical sensitivity is validated by the experiments. Furthermore, our simulations of the relative integrated intensities of the peaks associated with the nonlinear processes show that this type of simulation, in combination with experimental data, provides a useful tool for estimating the duration of ultra-short x-ray pulses.

  • 25. MacDonell, Ryan J.
    et al.
    Schalk, Oliver
    Stockholm University, Faculty of Science, Department of Physics.
    Geng, Ting
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Feifel, Raimund
    Hansson, Tony
    Stockholm University, Faculty of Science, Department of Physics.
    Schuurman, Michael S.
    Excited state dynamics of acrylonitrile: Substituent effects at conical intersections interrogated via time-resolved photoelectron spectroscopy and ab initio simulation2016In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 145, no 11, article id 114306Article in journal (Refereed)
    Abstract [en]

    We report a joint experimental and theoretical study on the photoinitiated ultrafast dynamics of acrylonitrile (AN) and two methylated analogs: crotonitrile (CrN) and methacrylonitrile (MeAN). Time-resolved photoelectron spectroscopy (TRPES) and ab initio simulation are employed to discern the conical intersection mediated vibronic dynamics leading to relaxation to the ground electronic state. Each molecule is pumped with a femtosecond pulse at 200 nm and the ensuing wavepackets are probed by means of one and two photon ionization at 267 nm. The predominant vibrational motions involved in the de-excitation process, determined by ab initio trajectory simulations, are an initial twisting about the C=C axis followed by pyramidalization at a carbon atom. The decay of the time-resolved photoelectron signal for each molecule is characterized by exponential decay lifetimes for the passage back to the ground state of 60 +/- 10, 86 +/- 11, and 97 +/- 9 fs for AN, CrN, and MeAN, respectively. As these results show, the excited state dynamics are sensitive to the choice of methylation site and the explanation for the observed trend may be found in the trajectory simulations. Specifically, since the pyramidalization motion leading to the conical intersection with the ground state is accompanied by the development of a partial negative charge at the central atom of the pyramidal group, the electron donation of the cyano group ensures that this occurs exclusively at the medial carbon atom. In this way, the donated electron density from the cyano group directs the wavepacket to a particular region of the intersection seam. The excellent agreement between the experimental and simulated TRPES spectra, the latter determined by employing trajectory simulations, demonstrates that this mechanistic picture is consistent with the spectroscopic results.

  • 26. Matsuda, Akitaka
    et al.
    Fushitani, Mizuho
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Zhaunerchyk, Vitali
    Stockholm University, Faculty of Science, Department of Physics.
    Hishikawa, Akiyoshi
    Multiple Explosion Pathways of the Deuterated Benzene Trication in 9-fs Intense Laser Fields2009In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 113, no 11, p. 2254-2260Article in journal (Refereed)
    Abstract [en]

    The fragmentation of deuterated benzene (CA) in ultrashort intense laser fields (9 fs, 1 x 10(15) W/cm(2)) is studied by the ion-coincidence momentum imaging technique. Five two-body and eight three-body Coulomb explosion pathways from the trication (C6D63+), associated with the deprotonation and ring-opening reactions, are identified. It is found from the fragment momentum correlation that all the observed three-body explosion processes proceed sequentially via the two-body Coulomb explosion forming molecular dications, CmDn2+, with (m,n) = (6,5), (5,5), (5,4), (4,4), (4,3), and (3,3), which further dissociate into pairs of monocations. The branching ratio of the fragmentation pathways estimated from the number of the observed coincidence events indicates that the fragmentation is nonstatistical.

  • 27. Mucke, M.
    et al.
    Zhaunerchyk, Vitali
    Stockholm University, Faculty of Science, Department of Physics. Uppsala University, Sweden; University of Gothenburg, Sweden.
    Frasinski, L. J.
    Squibb, R. J.
    Siano, M.
    Eland, J. H. D.
    Linusson, Per
    Stockholm University, Faculty of Science, Department of Physics.
    Salén, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    vab der Meulen, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Foucar, L.
    Ullrich, J.
    Motomura, K.
    Mondal, S.
    Ueda, K.
    Osipov, T.
    Fang, L.
    Murphy, B. F.
    Berrah, N.
    Bostedt, C.
    Bozek, J. D.
    Schorb, S.
    Messerschmidt, M.
    Glownia, J. M.
    Cryan, J. P.
    Coffee, R. N.
    Takahashi, O.
    Wada, S.
    Piancastelli, M. N.
    Richter, R.
    Prince, K. C.
    Feifel, R.
    Covariance mapping of two-photon double core hole states in C2H2 and C2H6 produced by an x-ray free electron laser2015In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 17, article id 073002Article in journal (Refereed)
    Abstract [en]

    Few-photon ionization and relaxation processes in acetylene (C2H2) and ethane (C2H6) were investigated at the linac coherent light source x-ray free electron laser (FEL) at SLAC, Stanford using a highly efficient multi-particle correlation spectroscopy technique based on a magnetic bottle. The analysis method of covariance mapping has been applied and enhanced, allowing us to identify electron pairs associated with double core hole (DCH) production and competing multiple ionization processes including Auger decay sequences. The experimental technique and the analysis procedure are discussed in the light of earlier investigations of DCH studies carried out at the same FEL and at third generation synchrotron radiation sources. In particular, we demonstrate the capability of the covariance mapping technique to disentangle the formation of molecular DCH states which is barely feasible with conventional electron spectroscopy methods.

  • 28. Oesterling, Sven
    et al.
    Schalk, Oliver
    Stockholm University, Faculty of Science, Department of Physics.
    Geng, Ting
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Hansson, Tony
    Stockholm University, Faculty of Science, Department of Physics.
    de Vivie-Riedle, Regina
    Substituent effects on the relaxation dynamics of furan, furfural and β-furfural: a combined theoretical and experimental approach2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, p. 2025-2035Article in journal (Refereed)
    Abstract [en]

    For the series furan, furfural and β-furfural we investigated the effect of substituents and their positioning on the photoinduced relaxation dynamics in a combined theoretical and experimental approach. Using time resolved photoelectron spectroscopy with a high intensity probe pulse, we can, for the first time, follow the whole deactivation process of furan through a two photon probe signal. Using the extended 2-electron 2-orbital model [Nenov et al., J. Chem. Phys., 2011, 135, 034304] we explain the formation of one central conical intersection and predict the influence of the aldehyde group of the derivatives on its geometry. This, as well as the relaxation mechanisms from photoexcitation to the final outcome was investigated using a variety of theoretical methods. Complete active space self consistent field was used for on-the-fly calculations while complete active space perturbation theory and coupled cluster theory were used to accurately describe critical configurations. Experiment and theory show the relaxation dynamics of furfural and β-furfural to be slowed down, and together they disclose an additional deactivation pathway, which is attributed to the nO lonepair state introduced with the aldehyde group.

  • 29. Pettersson, J. B. C.
    et al.
    Andersson, P. U.
    Hellberg, Fredrik
    Stockholm University, Faculty of Science, Department of Physics.
    Öjekull, J.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Dissociative recombination and excitation of D-5(+) by collisions with low-energy electrons2015In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 113, no 15-16, p. 2099-2104Article in journal (Refereed)
    Abstract [en]

    We report results from high-resolution studies of D-5(+) cluster ion collisions with low-energy electrons performed in a heavy ion storage ring. Absolute dissociative recombination (DR) and dissociative excitation (DE) cross sections were determined for the energy range from 0.0005 to 20eV. The DR cross sections were exceedingly large at low energies, and DR resulted in efficient internal energy redistribution and pronounced fragmentation with two main product channels: D-2+3D (0.62 +/- 0.03) and 2D(2)+D (0.35 +/- 0.01). The DR and DE cross sections were comparable in the energy range from 0.2 to 20eV, which suggest that the two processes follow similar dynamics and are competing outcomes of the ion-electron interaction. A simple picture of the recombination process of D-5(+) which captures the essential physics is suggested.

  • 30.
    Rebrov, Oleksii
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Kulyk, Kostiantyn
    Stockholm University, Faculty of Science, Department of Physics.
    Ryding, Mauritz
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Uggerud, Einar
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Chirally sensitive collision induced dissociation of proton-bound diastereomeric complexes of tryptophan and 2-butanol2017In: Chirality, ISSN 0899-0042, E-ISSN 1520-636X, Vol. 29, no 3-4, p. 115-119Article in journal (Refereed)
    Abstract [en]

    In this work we report the stereo-dependent collision-induced dissociation (CID) of proton-bound complexes of tryptophan and 2-butanol. The dissociation efficiency was measured as a function of collision energy in single collision mode. The homochiral complex was found to be less stable against CID than a heterochiral one. Additional gas dependence measurements were performed with diastereomeric complexes that confirm the findings.

  • 31.
    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)].

  • 32.
    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.

  • 33. Rohlen, J.
    et al.
    Lindahl, A. O.
    Hultgren, H.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Pegg, D. J.
    Hanstorp, D.
    Threshold behaviour in photodetachment into a final state with large negative polarizability2014In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 106, no 5, p. 53001-Article in journal (Refereed)
    Abstract [en]

    In a recent experiment, Lindahl et al. (Lindahl A. O. et al., Phys. Rev. Lett., 108 (2012) 033004) observed a new threshold behavior in the photodetachment of the potassium negative ion when the residual atom is left in the 5 (2)G state. Unfortunately the resonance close to threshold made it more difficult to apply the semi-classical model that was developed to describe the threshold behavior. In this paper we present a study of the threshold behavior of the 5 (2)G partial cross-section in the photodetachment of the sodium negative ion. The experiment was conducted using a collinear beams apparatus where the detection was performed using a resonance ionization scheme. We observe the same threshold behavior as in the previous experiment, but without any obfuscating resonance. The model derived in the previous paper is found to fit the observed cross-section up to 35 meV above threshold. The present experiment clearly demonstrates the threshold behaviour for the fundamental process of a free electron moving in the field of an atom with a large negative polarizability.

  • 34.
    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.

  • 35.
    Sahlén, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    van der Meulen, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard
    Stockholm University, Faculty of Science, Department of Physics.
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Feifel, Raimund
    Stockholm University, Faculty of Science, Department of Physics.
    Piancastelli, M. N.
    Fang, L.
    Murphy, B.
    Osipov, T.
    Berrah, N.
    Kukk, E.
    Ueda, K.
    Bozek, J. D.
    Bostedt, C.
    Wada, S.
    Richter, R.
    Feyer, V.
    Prince, K. C.
    Experimental Verification of the Chemical Sensitivity of Two-Site Double Core-Hole States Formed by an X-Ray Free-Electron Laser2012In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 108, no 15, p. 153003-Article in journal (Refereed)
    Abstract [en]

    We have performed x-ray two-photon photoelectron spectroscopy using the Linac Coherent Light Source x-ray free-electron laser in order to study double core-hole (DCH) states of CO2, N2O, and N-2. The experiment verifies the theory behind the chemical sensitivity of two-site DCH states by comparing a set of small molecules with respect to the energy shift of the two-site DCH state and by extracting the relevant parameters from this shift.

  • 36. Savee, John D.
    et al.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Mann, Jennifer E.
    Continetti, Robert E.
    Dissociative charge exchange dynamics of HN2+ and DN2+2009In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 131, no 13, p. 134301-Article in journal (Refereed)
    Abstract [en]

    Translational spectroscopy coupled with coincidence detection techniques has been used to study the dissociation dynamics of ground state H/D+N-2 products resulting from charge exchange between keV beams of HN2+/DN2+ and cesium. Analysis of the product kinetic energy release suggests that dissociation of HN2 and DN2 proceeds from initial populations in the (2)A '', 2 (2)A ', and 3s Rydberg electronic states of the neutral molecule. Although all three excited electronic states must eventually couple to the 1 (2)A ' ground state of HN2/DN2, the resulting dissociation dynamics exhibit a significant dependence on the initial electronic state. Potential mechanisms are discussed in light of the observed product kinetic energy release distributions.

  • 37.
    Schalk, Oliver
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Geng, Ting
    Stockholm University, Faculty of Science, Department of Physics.
    Thompson, Travis
    Baluyot, Noel
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Tapavicza, Enrico
    Hansson, Tony
    Stockholm University, Faculty of Science, Department of Physics.
    Cyclohexadiene Revisited: A Time-Resolved Photoelectron Spectroscopy and ab Initio Study2016In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 120, no 15, p. 2320-2329Article in journal (Refereed)
    Abstract [en]

    We have reinvestigated the excited state dynamics of cyclohexa-1,3-diene (CHD) with time-resolved photoelectron spectroscopy and fewest switches surface hopping molecular dynamics based on linear response time dependent density functional theory after excitation to the lowest lying pi pi* (1B) state. The combination of both theory and experiment revealed several new results: First, the dynamics progress on one single excited state surface. After an incubation time of 35 +/- 10 fs on the excited state, the dynamics proceed to the ground state in an additional 60 +/- 10 fs, either via a conrotatory ring-opening to hexatriene or back to the CHD ground state. Moreover, ring-opening predominantly occurs when the wavepacket crosses the region of strong nonadiabatic coupling with a positive velocity in the bond alternation coordinate. After 100 fs, trajectories remaining in the excited state must return to the CHD ground state. This extra time delay induces a revival of the photoelectron signal and is an experimental confirmation of the previously formulated model of two parallel reaction channels with distinct time constants. Finally, our simulations suggest that after the initially formed cis-Z-cis HT rotamer the trans-Z-trans isomer is formed, before the thermodynamical equilibrium of three possible rotamers is reached after 1 ps.

  • 38.
    Schalk, Oliver
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Josefsson, Ida
    Stockholm University, Faculty of Science, Department of Physics.
    Geng, Ting
    Stockholm University, Faculty of Science, Department of Physics.
    Richter, Robert
    Sa'adeh, Hanan
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Mucke, Melanie
    Dissociation kinetics of excited ions: PEPICO measurements of Os-3(CO)(12) - The 7-35 eV single ionization binding energy region2018In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 148, no 8, article id 084301Article in journal (Refereed)
    Abstract [en]

    In this article, we study the photoinduced dissociation pathways of a metallocarbonyl, Os-3(CO)(12), in particular the consecutive loss of CO groups. To do so, we performed photoelectron-photoion coincidence (PEPICO) measurements in the single ionization binding energy region from 7 to 35 eV using 45-eV photons. Zero-energy ion appearance energies for the dissociation steps were extracted by modeling the PEPICO data using the statistical adiabatic channel model. Upon ionization to the excited ionic states above 13 eV binding energy, non-statistical behaviorwas observed and assigned to prompt CO loss. Double ionization was found to be dominated by the knockout process with an onset of 20.9 similar to 0.4 eV. The oscillator strength is significantly larger for energies above 26.6 similar to 0.4 eV, corresponding to one electron being ejected from the Os3 center and one from the CO ligands. The cross section for double ionization was found to increase linearly up to 35 eV ionization energy, at which 40% of the generated ions are doubly charged.

  • 39.
    Schalk, Oliver
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Stenrup, M.
    Geng, Ting
    Stockholm University, Faculty of Science, Department of Physics.
    Lindh, R.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Feifel, R.
    Hansson, Tony
    Stockholm University, Faculty of Science, Department of Physics.
    Influence of Alkoxy Groups on the Photoinduced Dynamics of Organic Molecules Exemplified on Alkyl Vinyl Ethers2015In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 119, no 45, p. 11105-11112Article in journal (Refereed)
    Abstract [en]

    A series of different alkyl vinyl ethers is investigated to decipher the possible reaction channels upon photoexcitation to the pi 3s-Rydberg and the pi pi*-valence state at 200 nm using time-resolved photoelectron spectroscopy and on-the-fly time-dependent density functional theory dynamics simulations. The results indicate two possible relaxation pathways: (1) a radiationless decay through the pi pi*-state back to the ground state via torsion of the C=C double bond, in accordance with the dynamics found in ethylene; and (2) a fast dissociation of the C-O bond between the alkyl and the vinoxy group in the pi sigma*-state. The latter state can be accessed only after excitation to the pi 3s-Rydberg state (quantum yield of similar to 50% according to the dynamics simulations). Additionally, the excited state barrier leading to formation of a vinyl radical was found to be too high to be crossed. These results indicate that the dynamics of ethers crucially depend on the excitation wavelength and that the pi sigma*-state constitutes an important competitive reaction channel that leads to dissociation of the molecules.

  • 40.
    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.

  • 41.
    Schmidt, Henning
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Johansson, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard
    Stockholm University, Faculty of Science, Department of Physics.
    Geppert, Wolf
    Stockholm University, Faculty of Science, Department of Physics.
    Haag, Nicole
    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.
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Danared, Håkan
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Rensfelt, K.-G
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Liljeby, Leif
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Bagge, Lars
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Björkhage, Mikael
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Blom, Mikael
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Löfgren, Patrik
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Källberg, Anders
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Simonsson, Ansgar
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Paál, Andras
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    DESIREE as a new tool for interstellar ion chemistry2008In: International Journal of Astrobiology, ISSN 1473-5504, E-ISSN 1475-3006, Vol. 7, no 3-4, p. 205-208Article in journal (Refereed)
    Abstract [en]

    A novel cryogenic electrostatic storage device consisting of two ion-beam storage rings with a common straight section for studies of interactions between oppositely charged ions at low and well-defined relative velocities is under construction at Stockholm University. Here we consider the prospect of using this new tool to measure cross-sections and rate coefficients for mutual neutralization reactions of importance in interstellar ion chemistry in general and specifically in cosmic pre-biotic ion chemistry.

  • 42.
    Schmidt, Henning T.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Eklund, Gustav
    Stockholm University, Faculty of Science, Department of Physics.
    Chartkunchand, Kiattichart C.
    Stockholm University, Faculty of Science, Department of Physics.
    Anderson, Emma 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.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Kristiansson, Moa K.
    Stockholm University, Faculty of Science, Department of Physics.
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Reinhed, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Rosen, Stefan
    Stockholm University, Faculty of Science, Department of Physics.
    Simonsson, Ansgar
    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.
    Mannervik, Sven
    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.
    Rotationally Cold OH- Ions in the Cryogenic Electrostatic Ion-Beam Storage Ring DESIREE2017In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 119, no 7, article id 073001Article in journal (Refereed)
    Abstract [en]

    We apply near-threshold laser photodetachment to characterize the rotational quantum level distribution of OH- ions stored in the cryogenic ion-beam storage ring DESIREE at Stockholm University. We find that the stored ions relax to a rotational temperature of 13.4 +/- 0.2 K with 94.9 +/- 0.3% of the ions in the rotational ground state. This is consistent with the storage ring temperature of 13.5 +/- 0.5 K as measured with eight silicon diodes but in contrast to all earlier studies in cryogenic traps and rings where the rotational temperatures were always much higher than those of the storage devices at their lowest temperatures. Furthermore, we actively modify the rotational distribution through selective photodetachment to produce an OH- beam where 99.1 +/- 0.1% of approximately one million stored ions are in the J = 0 rotational ground state. We measure the intrinsic lifetime of the J = 1 rotational level to be 145 +/- 28 s.

  • 43.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    When electrons meet molecular ions and what happens next: Dissociative recombination from interstellar molecular clouds to internal combustion engines2008In: Mass spectrometry reviews (Print), ISSN 0277-7037, E-ISSN 1098-2787, Vol. 27, no 5, p. 485-530Article, review/survey (Refereed)
    Abstract [en]

    The interaction of matter with its environment is the driving force behind the evolution of 99% of the observed matter in the universe. The majority of the visible universe exists in a state of weak ionization, the so called fourth state of matter: plasma. Plasmas are ubiquitous, from those occurring naturally interstellar molecular clouds, cometary comae, circumstellar;shells, to those which are anthropic in origin: flames, combustion engines and fusion reactors. The evolution of these plasmas is driven by the interaction of the plasma constituents, the ions, and the electrons. One of the most important subsets of these reactions is electron-molecular ion recombination. This process is significant for two very important reasons. It is an ionization reducing reaction. removing two ionised species and Producing neutral products. Furthermore, these products may themselves be reactive radical species which can then further drive the evolution of the plasma. The rate at which the electron reacts with the ion depends on many parameters, for examples the collision energy. the internal energy of the ion, and the structure of the ion itself. Measuring these properties together with the manner in which the system breaks up, is therefore critical if the evolution of the environment is to be understood at all. Several techniques have been developed to study just such reactions to obtain the necessary information on the parameters. In this paper the focus will be on one the most recently developed of these, the Ion Storage Ring. together with the detection tools and techniques used to extract the necessary information from the reaction.

  • 44.
    Thomas, Richard D.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Ehlerding, Anneli
    Stockholm University, Faculty of Science, Department of Physics.
    Geppert, Wolf D.
    Stockholm University, Faculty of Science, Department of Physics.
    Hellberg, Fredrik
    Stockholm University, Faculty of Science, Department of Physics.
    Zhaunerchyk, Vitali
    Stockholm University, Faculty of Science, Department of Physics.
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Bahati, E.
    Bannister, M. E.
    Fogle, M. R.
    Vane, C. R.
    Dissociative recombination of LiH2+2014In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 89, no 5, p. 050701-Article in journal (Refereed)
    Abstract [en]

    In this paper, we report results regarding how LiH2+ fragments as a result of a low-energy collision with an electron (dissociative recombination), a reaction that contains only elements and particles created during the very first phase of the universe. The collision-energy-dependent reaction rate and cross sections show detailed structures, more so than predicted by theory, suggesting significant rovibrational coupling in the ion and a complex reaction surface. From the structure of the molecule, the reaction predominantly results in the formation of Li + H-2. However, 23% of the reaction flux leads to more interesting products, with 17% producing Li + 2H and 6% producing LiH + H. These last two channels break the strongest molecular bond in the system and, in the case of the latter channel, form a significantly weaker ionic bond. Possible reasons behind this interesting behavior are discussed, together with the interaction between the available reaction channels.

  • 45.
    Thomas, Richard D.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Kashperka, Iryna
    Stockholm University, Faculty of Science, Department of Physics.
    Vigren, Erik
    Stockholm University, Faculty of Science, Department of Physics.
    Geppert, Wolf D.
    Stockholm University, Faculty of Science, Department of Physics.
    Hamberg, Mathias
    Stockholm University, Faculty of Science, Department of Physics.
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    af Ugglas, Magnus
    Stockholm University, Faculty of Science, Department of Physics.
    Zhaunerchyk, Vitali
    Stockholm University, Faculty of Science, Department of Physics.
    Dissociative Recombination of CH4+2013In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 117, no 39, p. 9999-10005Article in journal (Refereed)
    Abstract [en]

    CH4+ is an important molecular ion in the astrochemistry of diffuse clouds, dense clouds, cometary comae, and planetary ionospheres However, the rate of one of the common destruction mechanisms for molecular ions in these regions, dissociative recombination (DR), is somewhat uncertain. Here, we present absolute measurements for the DR of CH4+ made using the heavy ion storage ring CRYRING hi Stockholm, Sweden. From our collision energy dependent cross sections, we infer a thermal rate constant of k(T-e) = 1.71(+/- 0.02) X 10(-6)(T-e/300)(-0.66(+/- 0.02)) cm(3) s(-1) over the region of electron temperatures 10 <= T-e <= 1000 K. At low collision energies, we have measured the branching fractions of the DR products to be CH4 (0.00 +/- 0.00); CH3 + H (0.18 +/- 0.03); CH2 + 2H (0.51 +/- 0.03); CH2 + H-2 (0.06 +/- 0.01); CH + H-2 + H (0.23 +/- 0.01); and CH + 2H(2) (0.02 +/- 0.01), indicating that two or more C-H bonds are broken in similar to 80% of all collisions.

  • 46.
    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.

  • 47.
    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).

  • 48.
    Thomas, Richard
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Kashperka, I.
    Stockholm University, Faculty of Science, Department of Physics.
    Vigren, Erik
    Stockholm University, Faculty of Science, Department of Physics.
    Geppert, Wolf D.
    Stockholm University, Faculty of Science, Department of Physics.
    Hamberg, M.
    Stockholm University, Faculty of Science, Department of Physics.
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    af Ugglas, Magnus
    Stockholm University, Faculty of Science, Department of Physics.
    Zhaunerchyk, Vitali
    Stockholm University, Faculty of Science, Department of Physics.
    Indriolo, N.
    Yagi, K.
    Hirata, S.
    McCall, B. J.
    DISSOCIATIVE RECOMBINATION OF VIBRATIONALLY COLD CH+3 AND INTERSTELLAR IMPLICATIONS2012In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 758, no 1, p. 55-Article in journal (Refereed)
    Abstract [en]

    CH3+ is an important molecular ion in the astrochemistry of diffuse clouds, dense clouds, cometary comae, and planetary ionospheres. However, the rate of one of the major destruction mechanisms of CH3+, dissociative recombination (DR), has long been uncertain, hindering the use of CH3+ as an astrochemical probe. Here, we present the first absolute measurement of the DR of vibrationally cold CH3+, which has been made using the heavy storage ring CRYRING in Stockholm, Sweden. From our collision-energy-dependent cross sections, we infer a thermal rate constant of k(T) = 6.97(+/- 0.03) x 10(-7)(T/300)(-0.61(+/- 0.01)) cm(3) s(-1) over the region 10 K <= T <= 1000 K. At low collision energies, we have measured the branching fractions of the DR products to be CH3 (0.00(- 0.00)(+ 0.01)), CH2 + H (0.35(-0.01)(+ 0.01)), CH + 2H (0.20(-0.02)(+0.02)), CH + H-2 (0.10(-0.01)(+0.01)), and C + H-2 + H (0.35(-0.02)(+ 0.01)), indicating that two or more C-H bonds are broken in 65% of all collisions. We also present vibrational calculations which indicate that the CH3+ ions in the storage ring were relaxed to the vibrational ground state by spontaneous emission during the storage time. Finally, we discuss the implications of these new measurements for the observation of CH3+ in regions of the diffuse interstellar medium where CH+ is abundant.

  • 49. Tom, Brian A.
    et al.
    Zhaunerchyk, Vitali
    Stockholm University, Faculty of Science, Department of Physics.
    Wiczer, Michael B.
    Mills, Andrew A.
    Crabtree, Kyle N.
    Kaminska, Magdalena
    Stockholm University, Faculty of Science, Department of Physics.
    Geppert, Wolf D.
    Stockholm University, Faculty of Science, Department of Physics.
    Hamberg, Mathias
    Stockholm University, Faculty of Science, Department of Physics.
    af Ugglas, Magnus
    Stockholm University, Faculty of Science, Department of Physics.
    Vigren, Erik
    Stockholm University, Faculty of Science, Department of Physics.
    van der Zande, Wim J.
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    McCall, Benjamin J.
    Dissociative recombination of highly enriched para-H-3(+)2009In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 130, no 3, p. 31101-Article in journal (Refereed)
    Abstract [en]

    The determination of the dissociative recombination rate coefficient of H-3(+) has had a turbulent history, but both experiment and theory have recently converged to a common value. Despite this convergence, it has not been clear if there should be a difference between the rate coefficients for ortho-H-3(+) and para-H-3(+). A difference has been predicted theoretically and could conceivably impact the ortho:para ratio of H-3(+) in the diffuse interstellar medium, where H-3(+) has been widely observed. We present the results of an experiment at the CRYRING ion storage ring in which we investigated the dissociative recombination of highly enriched (similar to 83.6%) para-H-3(+) using a supersonic expansion source that produced ions with T-rot similar to 60-100 K. We observed an increase in the low energy recombination rate coefficient of the enriched para-H-3(+) by a factor of similar to 1.25 in comparison to H-3(+) produced from normal H-2 (ortho:para=3:1). The ratio of the rate coefficients of pure para-H-3(+) to that of pure ortho-H-3(+) is inferred to be similar to 2 at low collision energies; the corresponding ratio of the thermal rate coefficients is similar to 1.5 at electron temperatures from 60 to 1000 K. We conclude that this difference is unlikely to have an impact on the interstellar ortho:para ratio of H-3(+).

  • 50. Vane, C. R.
    et al.
    Bahati, E. M.
    Bannister, M. E.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Electron-impact dissociation of CH2+ ions: Measurement of CH+ and C+ fragment ions2007In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 75, no 5, p. 52715-Article in journal (Refereed)
    Abstract [en]

    Absolute cross sections for electron-impact dissociation of CH2+ producing CH+ and C+ fragment ions were measured in the 3-100 eV range using a crossed electron-ion beams technique with total uncertainties of about 11% near the cross section peak. The cross sections are nearly identical for energies above 15 eV, but they are dramatically different at lower energies. The CH+ channel exhibits a strong peak rising from an observed threshold of about 6 eV; the C+ channel is relatively flat down to the lowest measured energy. Ionization cross sections for the CH2+ ion are also presented.

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