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  • 1.
    Akram, Nadeem
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Zhang, Hongqiang
    Stockholm University, Faculty of Science, Department of Physics.
    Soroka, Inna Leonidovna
    Stockholm University, Faculty of Science, Department of Physics.
    Trautmann, Christina
    Schuch, Reinhold
    Stockholm University, Faculty of Science, Department of Physics.
    Transmission of highly charged ions through phlogopite-mica nanocapillaries of rectangular cross-sectionIn: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455Article in journal (Refereed)
    Abstract [en]

    We measured the transmission of Ne7+ ions through nanocapillaries of rectangular cross-section produced by chemical etching of ion tracks in phlogopite mica. The two dimensional transmitted profiles are rhombic for tilt angles within the geometrical opening angle given by the aspect ratio of the short side of the rectangular cross section of the capillaries. The transmission depends on the incident charge indicating that the rhombic shape is due to the image charge of uncharged rectangular capillaries. Above a critical charge deposition, the rhombic shape tends to be smeared out. Ions are also transmitted at angles larger than the geometrical opening angle giving evidence for the guiding effect.

  • 2.
    Ali, Safdar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Mahmood, Sultan
    Stockholm University, Faculty of Science, Department of Physics.
    Orban, Istvan
    Stockholm University, Faculty of Science, Department of Physics.
    Tashenov, Stanislav
    Stockholm University, Faculty of Science, Department of Physics.
    Li, Y. M.
    Wu, Z.
    Schuch, Reinhold
    Stockholm University, Faculty of Science, Department of Physics.
    Electron-ion recombination of H- and He-like sulfur2011In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 44, no 22, p. 225203-Article in journal (Refereed)
    Abstract [en]

    Electron-ion recombination of sulfur ions with electrons in the energy range of 1.6-3 keV was studied at the Stockholm Refrigerated Electron Beam Ion Trap. We obtained the KLn dielectronic recombination (DR) cross sections up to n = 5 for H-like and He-like sulfur ions by observing the x-rays from the trapped ions. A fully relativistic distorted wave approximation method was used for calculating the DR cross sections, while the resonance energies were obtained with a multiconfiguration Dirac-Fock approach using the GRASP II code. The calculations agree with the experimental results within the experimental error bars. Additionally, the obtained total DR resonance strengths were used to check the behaviour of a scaling formula for low-Z, He-like iso-electronic sequence (Watanabe et al 2001 J. Phys. B: At. Mol. Opt. Phys. 34 5095).

  • 3.
    Argenti, Luca
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Moccia, Roberto
    Nondipole effects in helium photoionization2010In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 43, no 23, article id 235006Article in journal (Refereed)
    Abstract [en]

    An accurate calculation of the nondipole anisotropy parameter gamma in the photoionization of helium below the N = 2 threshold is presented. The calculated results are in fairly good agreement with the experimental results of Krassig et al (2002 Phys. Rev. Lett. 88 203002), but not as good as the accuracy of the calculation should have warranted. A careful examination of the possible causes for the observed discrepancies between theory and experiment seems to rule out any role either of the multipolar terms higher than the electric quadrupole, or of the singlet-triplet spin-orbit mixing. It is argued that such discrepancies might have an instrumental origin, due to the difficulty of measuring vanishingly small total cross sections sigma(tot) with the required accuracy. In such eventuality, it might be more appropriate to use a parameter other than gamma, such as for instance the drag current, to measure the nondipole anisotropy of the photoelectron angular distribution.

  • 4. Aumayr, Friedrich
    et al.
    Ueda, Kiyoshi
    Sokell, Emma
    Schippers, Stefan
    Sadeghpour, Hossein
    Merkt, Frederic
    Gallagher, Thomas F.
    Dunning, F. Barry
    Scheier, Paul
    Eche, Olof
    Kirchner, Tom
    Fritzsche, Stephan
    Surzhykov, Andrey
    Ma, Xinwen
    Rivarola, Roberto
    Fojon, Omar
    Tribedi, Lokesh
    Lamour, Emily
    Lopez-Urrutia, Jose R. Crespo
    Litvinov, Yuri A.
    Shabaev, Vladimir
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Schleberger, Marika
    Wilhelm, Richard A.
    Azuma, Toshiyuki
    Boduch, Philippe
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Stoehlker, Thomas
    Roadmap on photonic, electronic and atomic collision physics: III. Heavy particles2019In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 52, no 17, article id 171003Article in journal (Refereed)
    Abstract [en]

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

  • 5.
    Bäckström, Erik
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Nilsson, H.
    Engström, L.
    Hartman, H.
    Mannervik, Sven
    Stockholm University, Faculty of Science, Department of Physics.
    Experimentally determined oscillator strengths in Rh II2013In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 46, no 20, p. 205001-Article in journal (Refereed)
    Abstract [en]

    This paper presents new experimentally determined branching fractions and oscillator strengths (log gf) for lines originating from 17 levels belonging to 5 terms of the first excited odd configuration 4d(7)(D-4) 5p in Rh II. The intensity calibrated spectra of Rh II have been recorded with a Fourier transform spectrometer between 25000 and 45000 cm(-1) (2200-4000 angstrom). In this region, 49 lines have been identified and measured. By combining the branching fractions obtained from the spectra with previously measured lifetimes, log gf values are reported. The new results are compared with previous theoretical work.

  • 6.
    Carette, Thomas
    et al.
    Stockholm University, Faculty of Science, Department of Physics. University Libre Brussels .
    Godefroid, M. R.
    Isotope shift on the chlorine electron affinity revisited by an MCHF/CI approach2013In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 46, no 9, p. 095003-Article in journal (Refereed)
    Abstract [en]

    Today, the electron affinity is experimentally well known for most of the elements and is a useful guideline for developing ab initio computational methods. However, the measurements of isotope shifts on the electron affinity are limited by both resolution and sensitivity. In this context, theory is of great help to further our knowledge and understanding of atomic structures, even though correlation plays a dominant role in negative ions' properties and, particularly, in the calculation of the specific mass shift contribution. This study solves the longstanding discrepancy between calculated and measured specific mass shifts on the electron affinity of chlorine.

  • 7.
    Dahlström, J. Marcus
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    L'Huillier, A.
    Maquet, A.
    Introduction to attosecond delays in photoionization2012In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 45, no 18, p. 183001-Article in journal (Refereed)
    Abstract [en]

    This tutorial presents an introduction to the interaction of light and matter on the attosecond timescale. Our aim is to detail the theoretical description of ultra-short time delays and to relate these to the phase of extreme ultraviolet (XUV) light pulses and to the asymptotic phaseshifts of photoelectron wave packets. Special emphasis is laid on time-delay experiments, where attosecond XUV pulses are used to photoionize target atoms at well-defined times, followed by a probing process in real time by a phase-locked, infrared laser field. In this way, the laser field serves as a 'clock' to monitor the ionization event, but the observable delays do not correspond directly to the delay associated with single-photon ionization. Instead, a significant part of the observed delay originates from a measurement induced process, which obscures the single-photon ionization dynamics. This artefact is traced back to a phaseshift of the above-threshold ionization transition matrix element, which we call the continuum-continuum phase. It arises due to the laser-stimulated transitions between Coulomb continuum states. As we shall show here, these measurement-induced effects can be separated from the single-photon ionization process, using analytical expressions of universal character, so that eventually the attosecond time delays in photoionization can be accessed.

  • 8.
    Dahlström, J. Marcus
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Max Planck Society, Germany; Centre for Free Electron Laser Science, Germany.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Study of attosecond delays using perturbation diagrams and exterior complex scaling2014In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 47, no 12, p. 124012-Article in journal (Refereed)
    Abstract [en]

    We describe in detail how attosecond delays in laser-assisted photoionization can be computed using perturbation theory based on two-photon matrix elements. Special emphasis is laid on above-threshold ionization, where the electron interacts with an infrared field after photoionization by an extreme ultraviolet field. Correlation effects are introduced using diagrammatic many-body theory to the level of the random-phase approximation with exchange. Our aim is to provide an ab initio route to correlated multi-photon processes that are required for an accurate description of experiments on the attosecond time scale. Here, our results are focused on photoionization of the M-shell of argon atoms, where experiments have been carried out using the so-called reconstruction of attosecond beating by the two-photon interference transitions technique. An influence of autoionizing resonances in attosecond delay measurements is observed. Further, it is shown that the delay depends on both detection angle of the photoelectron and energy of the probe photon.

  • 9. Della Picca, R.
    et al.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Multicolor XUV above threshold ionization of argon2015In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 48, no 24, article id 245202Article in journal (Refereed)
    Abstract [en]

    Argon photo-electron spectra produced by short-pulse extreme ultraviolet radiation, and with particular emphasis on the two-photon absorption region, is analyzed theoretically. The electromagnetic pulse is modeled to resemble experimentally available pulses and is built from a range of high-harmonics from an 800 nm laser. The photo-electron spectra show a characteristic peak structure due to the absorption of different combinations of photons, where the relative peak intensity is very sensitive to both the XUV pulse parameters and the target description. The theoretical result is further compared with experimental data, and good qualitative agreement is found.

  • 10. Ekholm, V.
    et al.
    Chiuzbǎian, G. S.
    Såthe, C.
    Nicolaou, A.
    Guarise, M.
    Simon, M.
    Jaouen, N.
    Lüning, J.
    Hague, C. F.
    Gel'mukhanov, F.
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Björneholm, O.
    Rubensson, J.-E.
    Core-hole localization and ultra-fast dissociation in SF62020In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 53, no 18, article id 185101Article in journal (Refereed)
    Abstract [en]

    Resonant inelastic x-ray scattering spectra excited at the fluorine K resonances of SF(6)have been recorded. While a small but significant propensity for electronically parity-allowed transitions is found, the observation of parity-forbidden electronic transitions is attributed to vibronic coupling that breaks the global inversion symmetry of the electronic wavefunction and localizes the core hole. The dependence of the scattering cross section on the polarization of the incident radiation and the scattering angle is interpreted in terms of local pi/sigma symmetry around the S-F bond. This symmetry selectivity prevails during the dissociation that occurs during the scattering process.

  • 11.
    Gatchell, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Knockout driven reactions in complex molecules and their clustersIn: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455Article in journal (Refereed)
    Abstract [en]

    Energetic ions lose some of their kinetic energies when interacting with electrons or nuclei in matter. Here, we discuss combined experimental and theoretical studies on such impulse driven reactions in Polycyclic Aromatic Hydrocarbons (PAHs), fullerenes, and pure or mixed clusters of these molecules. These studies show that the nature of excitation is important for how complex molecular systems respond to ion/atom impact. Rutherford-like nuclear scattering processes may lead to prompt atom knockout and formation of highly reactive fragments, while heating of the molecular electron clouds in general lead to formation of more stable and less reactive fragments. In this topical review, we focus on recent studies of knockout driven reactions, and present new calculations of the angular dependent threshold (displacement) energies for such processes in PAHs. The so formed fragments may efficiently form covalent bonds with neighboring molecules in clusters. These unique molecular growth processes may be important in astrophysical environments such as low velocity shock waves. 

  • 12.
    Gatchell, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Knockout driven reactions in complex molecules and their clusters2016In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 49, no 16, article id 162001Article, review/survey (Refereed)
    Abstract [en]

    Energetic ions lose some of their kinetic energy when interacting with electrons or nuclei in matter. Here, we discuss combined experimental and theoretical studies on such impulse driven reactions in polycyclic aromatic hydrocarbons (PAHs), fullerenes, and pure or mixed clusters of these molecules. These studies show that the nature of excitation is important for how complex molecular systems respond to ion/atom impact. Rutherford-like nuclear scattering processes may lead to prompt atom knockout and formation of highly reactive fragments, while heating of the molecular electron clouds in general lead to formation of more stable and less reactive fragments. In this topical review, we focus on recent studies of knockout driven reactions, and present new calculations of the angular dependent threshold (displacement) energies for such processes in PAHs. The so-formed fragments may efficiently form covalent bonds with neighboring molecules in clusters. These unique molecular growth processes may be important in astrophysical environments such as low velocity shock waves.

  • 13.
    Gudmundsson, Magnus
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Fischer, D.
    Stockholm University, Faculty of Science, Department of Physics.
    Haag, N.
    Stockholm University, Faculty of Science, Department of Physics.
    Johansson, H. A. B.
    Stockholm University, Faculty of Science, Department of Physics.
    Misra, Deepankar
    Stockholm University, Faculty of Science, Department of Physics.
    Reinhed, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt-Boecking, H.
    Schuch, Reinhold
    Stockholm University, Faculty of Science, Department of Physics.
    Schoeffler, M.
    Stochkel, K.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Angular scattering in fast ion-atom electron transfer collisions: projectile wave diffraction and Thomas mechanisms2010In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 43, no 18, p. 185209-Article in journal (Refereed)
    Abstract [en]

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

  • 14.
    Gudmundsson, Magnus
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Fischer, Daniel
    Misra, Deepankar
    Källberg, Anders
    Simonsson, Ansgar
    Stöchkel, Kristian
    Cederquist, Henrik
    Schmidt, Henning T.
    Two-site double-core-hole states formed when fast protons capture electrons from aligned N22011In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 44, no 17, p. 175201-Article in journal (Refereed)
    Abstract [en]

    We report on an experimental investigation of 1.04 MeV H++N2 electron transfer collisions. The fast protons were stored in the electron-cooler ion-storage ring, CRYRING and the molecular nitrogen target was provided with a supersonic gas jet. We report momentum distributions of atomic nitrogen dissociation products Nq+ with charge states q+ (q=1, 2, 3) which are detected in coincidence with neutralized projectiles. Further, we investigate the influence of the angle between the direction of the incoming projectile beam and the target molecular axis. The orientation of the latter is determined a posteriorly from the momentum vector of one emitted atomic nitrogen fragment ion. We find signicantly higher total yields, dominated by N+, of charged atomic dissociation products when the N2 molecular axis is perpendicular to the incoming H+-beam. The relative contributions from N2+- and N3+- fragments, however, are strongest when the N2 axis is aligned -or close to aligned- with the ion beam. This, we suggest, is due to increased probabilities for formation of two-site double-core-hole states.

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  • 15. Guenot, D.
    et al.
    Kroon, D.
    Balogh, E.
    Larsen, E. W.
    Kotur, M.
    Miranda, M.
    Fordell, T.
    Johnsson, P.
    Mauritsson, J.
    Gisselbrecht, M.
    Varju, K.
    Arnold, C. L.
    Carette, Thomas
    Stockholm University, Faculty of Science, Department of Physics. University Libre Brussels, Belgium.
    Kheifets, A. S.
    Lindroth, E.
    L'Huillier, A.
    Dahlström, J. Marcus
    Stockholm University, Faculty of Science, Department of Physics. Center for Free-Electron Laser Science, Germany; Max Planck Institute for the Physics of Complex Systems, Germany.
    Measurements of relative photoemission time delays in noble gas atoms2014In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 47, no 24, p. 245602-Article in journal (Refereed)
    Abstract [en]

    We determine relative photoemission time delays between valence electrons in different noble gas atoms (Ar, Ne and He) in an energy range between 31 and 37 eV. The atoms are ionized by an attosecond pulse train synchronized with an infrared laser field and the delays are measured using an interferometric technique. We compare our results with calculations using the random phase approximation with exchange and multi-configurational Hartree-Fock. We also investigate the influence of the different ionization angular channels.

  • 16.
    Hedberg, Hanae Miyano
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Nkambule, Sifiso
    Stockholm University, Faculty of Science, Department of Physics.
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    Landau-Zener studies of mutual neutralization in collisions of H+ + H- and Be+ + H-2014In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 47, no 22, article id 225206Article in journal (Refereed)
    Abstract [en]

    Semi-classical Landau-Zener studies of mutual neutralization reactions in low-energy H+ + H- and Be+ + H- collisions are performed. Avoided crossings between ionic and covalent states occurring at large internuclear distances are considered, and electronic couplings between these states are estimated using different semi-empirical and ab initio methods and tested on the H+ + H- reaction. The method is then applied to compute the cross sections and final state distributions for mutual neutralization in collisions of H- with Be+. These are reactions that might be important for the modeling of the fusion edge plasma of the divertor of ITER.

  • 17. Ingle, R. A.
    et al.
    Banerjee, Ambar
    Stockholm University, Faculty of Science, Department of Physics.
    Bacellar, C.
    Barillot, T. R.
    Longetti, L.
    Coreno, M.
    de Simone, M.
    Zuccaro, F.
    Poletto, L.
    Miotti, P.
    Röder, A.
    Stolow, A.
    Schuurman, M. S.
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Chergui, M.
    Carbon K-edge x-ray emission spectroscopy of gas phase ethylenic molecules2022In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 55, no 4, article id 044001Article in journal (Refereed)
    Abstract [en]

    We report on the C K-edge x-ray absorption spectra and the resonant (RXES) and non-resonant (NXES) x-ray emission spectra of ethylene, allene and butadiene in the gas phase. The RXES and NXES show clear differences for the different molecules. Overall both types of spectra are more structured for ethylene and allene, than for butadiene. Using density functional theory–restricted open shell configuration interaction single calculations, we simulate the spectra with remarkable agreement with the experiment. We identify the spectral features as being due to transitions involving localised 1s orbitals. For allene, there are distinct spectral bands that reflect transitions predominantly from either the central or terminal carbon atoms. These results are discussed in the context of ultrafast x-ray studies aimed at detecting the passage through conical intersections in polyatomic molecules.

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  • 18.
    Jonsell, Svante
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Charlton, M.
    van der Werf, D. P.
    The role of antihydrogen formation in the radial transport of antiprotons in positron plasmas2016In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 49, no 13, article id 134004Article in journal (Refereed)
    Abstract [en]

    Simulations have been performed of the radial transport of antiprotons in positron plasmas under ambient conditions typical of those used in antihydrogen formation experiments. The parameter range explored includes several positron densities and temperatures, as well as two different magnetic fields (1 and 3 T). Computations were also performed in which the antihydrogen formation process was artificially suppressed in order to isolate its role from other collisional sources of transport. The results show that, at the lowest positron plasma temperatures, repeated cycles of antihydrogen formation and destruction are the dominant source of radial (cross magnetic field) transport, and that the phenomenon is an example of anomalous diffusion.

  • 19.
    Kapshai, Valery
    et al.
    Gomel State University.
    Shilyaeva, Ksenia
    Stockholm University, Faculty of Science, Department of Physics.
    Elander, Nils
    Stockholm University, Faculty of Science, Department of Physics.
    Integral equations for different wavefunctions and their use in finding resonances2009In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 42, no 4, p. 044001-Article in journal (Refereed)
  • 20.
    Larson, Jonas
    Stockholm University, Faculty of Science, Department of Physics.
    Integrability versus quantum thermalization2013In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 46, no 22, p. 224016-Article in journal (Refereed)
    Abstract [en]

    Non-integrability is often taken as a prerequisite for quantum thermalization. Still, a generally accepted definition of quantum integrability is lacking. With the basis in the driven Rabi model we discuss this careless usage of the term 'integrability' in connection to quantum thermalization. The model would be classified as non-integrable according to the most commonly used definitions, for example, the only preserved quantity is the total energy. Despite this fact, a thorough analysis conjectures that the system will not thermalize. Thus, our findings suggest first of all (i) that care should be paid when linking non-integrability with thermalization, and secondly (ii) that the standardly used definitions for quantum integrability are unsatisfactory.

  • 21.
    Larson, Jonas
    et al.
    Stockholm University, Faculty of Science, Department of Physics. University of Cologne, Germany.
    O'Dell, Duncan H. J.
    Chaos in circuit QED: decoherence, localization and nonclassicality2013In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 46, no 22, p. 224015-Article in journal (Refereed)
    Abstract [en]

    We study the open system dynamics of a circuit quantum electrodynamics (QED) model operating in the ultrastrong coupling regime. If the resonator is pumped periodically in time the underlying classical system is chaotic. Indeed, the periodically driven Jaynes-Cummings model in the Born-Oppenheimer approximation resembles a Duffing oscillator which in the classical limit is a well-known example of a chaotic system. Detection of the field quadrature of the output field acts as an effective position measurement of the oscillator. We address how such detection affects the quantum chaotic evolution in this bipartite system. We differentiate between single measurement realizations and ensembles of repeated measurements. In the former case a measurement/decoherence induced localization effect is encountered, while in the latter this localization is almost completely absent. This is in marked contrast to numerous earlier works discussing the quantum-classical correspondence in measured chaotic systems. This lack of a classical correspondence under relatively strong measurement induced decoherence is attributed to the inherent quantum nature of the qubit subsystem and in particular to the quantum correlations between the qubit and the field which persist despite the decoherence.

  • 22.
    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.

  • 23. Laskowski, Wieslaw
    et al.
    Wiesniak, Marcin
    Zukowski, Marek
    Bourennane, Mohamed
    Stockholm University, Faculty of Science, Department of Physics.
    Weinfurter, Harald
    Interference contrast in multisource few-photon optics2009In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 42, no 11, p. 114004-Article in journal (Refereed)
    Abstract [en]

    Many recent experiments employ several parametric down-conversion (PDC) sources to get multiphoton interference. Such interference has applications in quantum information. We study here how effects due to photon statistics, misalignment and partial distinguishability of the PDC pairs originating from different sources may lower the interference contrast in multiphoton experiments.

  • 24. Lotfipour, H.
    et al.
    Allameh, Z.
    Roknizadeh, R.
    Heydari, Hoshang
    Stockholm University, Faculty of Science, Department of Physics.
    Two schemes for characterization and detection of the squeezed light: dynamical Casimir effect and nonlinear materials2016In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 49, no 6, article id 065503Article in journal (Refereed)
    Abstract [en]

    Using two different schemes, a non-classical-squeezed state of light is detected and characterized. In the first scheme, in a one-dimensional cavity with a moving mirror (non-stationary Casimir effect) in the principal mode, we study the photon generation rate for two modes (squeezed and coherent state) of a driving field. Since the cavity with the moving mirror (similar to an optomechanical system) can be considered an analogue to a Kerr-like medium, in the second scheme, the probability amplitude for multi-photon absorption in a nonlinear (Kerr) medium will be quantum mechanically calculated. It is shown that because of the presence of nonlinear effects, the responses of these two systems to the squeezed versus coherent state are considerably distinguishable. The drastic difference between the results of these two states of light can be viewed as a proposal for detecting non-classical states.

  • 25. Maiorova, A. V.
    et al.
    Surzhykov, A.
    Tashenov, Stanislav
    Stockholm University, Faculty of Science, Department of Physics.
    Shabaev, V. M.
    Fritzsche, S.
    Plunien, G.
    Stoehlker, Th.
    Polarization studies on the two-step radiative recombination of highly charged, heavy ions2009In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 42, no 12, article id 125003Article in journal (Refereed)
    Abstract [en]

    Radiative recombination of a free electron into an excited state of a bare, high-Z ion is studied, together with its subsequent decay, within the framework of the density matrix theory and Dirac's relativistic equation. Special attention is paid to the polarization and angular correlations between the recombination and the decay photons. In order to perform a systematic analysis of these correlations the general expression for the double-differential recombination cross section is obtained by making use of the resonance approximation. Based on this expression, detailed computations for the linear polarization of x-ray photons emitted in the (e, 2 gamma) two-step recombination of uranium ions U92+ are carried out for a wide range of projectile energies.

  • 26.
    Orban, Istvan
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Glans, Peter
    Department of Engineering, Physics and Mathematics, Mid Sweden University.
    Schuch, Reinhold
    Stockholm University, Faculty of Science, Department of Physics.
    Spectroscopic study of doubly excited states in Mg-likeSi using dielectronic recombination2007In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 40, no 5, p. 1063-1080Article in journal (Refereed)
    Abstract [en]

    We present calculated and experimentally derived electron–ion recombinationrate coefficients for Na-like Si IV, recombining into Mg-like Si III, andprovide accurate spectroscopic data for doubly excited states located above theionization threshold of Si III. The experimental recombination rate coefficientswere measured in a merged-beam-type experiment at the heavy-ion storagering CRYRING at the Manne Siegbahn Laboratory in Stockholm. Changing theelectron–ion relative energy from 0 to 20 eV we covered the energy region fromthe first to the third ionization threshold. We find that even for the low-chargedSi2+ ion, a relativistic many-body perturbation theory calculation is necessary,to describe the recombination rate coefficients in the low-energy region, up to1.5 eV, satisfactorily. Doubly excited states, forbidden to form in LS coupling,are responsible for the most prominent dielectronic recombination resonances atlow energies and contribute with 40% to the strength. Several wide resonancesgive rise to a plateau-like formation in the recombination spectrum. A broaderenergy range, up to 6.7 eV, was covered with a non-relativistic many-bodycalculation. This range contains, in addition to 3pn resonances, severalresonances of the type 3dn, with the LS-forbidden 3d2 3F states giving riseto a strong, isolated peak at 2.976 eV. The NIST database lists eleven doublyexcited states of Si III with energy positions deviating considerably from ourdetermination. Since the listed lines are also not fully matching those with thelargest fluorescence yields it must be concluded that they are misidentified.

  • 27. Pabst, Stefan
    et al.
    Dahlström, Jan Marcus
    Stockholm University, Faculty of Science, Department of Physics.
    Characterizing attosecond pulses in the soft x-ray regime2017In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 50, no 10, article id 104002Article in journal (Refereed)
    Abstract [en]

    Attosecond x-ray pulses offer unprecedented opportunities for probing and triggering new types of ultrafast motion. At the same time, pulse characterization of x-rays presents new challenges that do not exist in the UV regime. Inner-shell ionization is the dominant ionization mechanism for x-rays and it is followed by secondary processes like fluorescence, Auger decay, and shake-up. In general, we find that inner-shell ionization and secondary processes can create additional delay-dependent modulations that will affect pulse reconstruction schemes. Our recently proposed pulse characterization method (Pabst and Dahlstrom 2016 Phys. Rev. A 94 013411), where a bound electron wavepacket is sequentially photoionized by the attosecond pulse, can be adapted to mitigate the impact of these effects, thus opening up an avenue for reliable pulse reconstruction in the x-ray regime.

  • 28. Palatchi, Caryn
    et al.
    Dahlström, J. Marcus
    Stockholm University, Faculty of Science, Department of Physics. Max Planck Institute for the Physics of Complex Systems, Germany; Center for Free-Electron Laser Science, Germany.
    Kheifets, A. S.
    Ivanov, I. A.
    Canaday, D. M.
    Agostini, P.
    DiMauro, L. F.
    Atomic delay in helium, neon, argon and krypton2014In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 47, no 24, p. 245003-Article in journal (Refereed)
    Abstract [en]

    Photoionization by an eXtreme UltraViolet (XUV) attosecond pulse train (APT) in the presence of an infrared pulse (RABBITT method) conveys information about the atomic photoionization delay. By taking the difference of the spectral delays between pairs of rare gases (Ar,He), (Kr,He) and (Ne,He) it is possible to eliminate in each case the larger group delay ('attochirp') associated with the APT itself and obtain the Ar, Kr and Ne Wigner delays referenced to model calculations of the He delay. In this work we measure how the delays vary as a function of XUV photon energy but we cannot determine the absolute delay difference between atoms due to lack of precise knowledge of the initial conditions. The extracted delays are compared with several theoretical predictions and the results are consistent within 30 as over the energy range from 10 to 50 eV. An 'effective' Wigner delay over all emission angles is found to be more consistent with our angle-integrated measurement near the Cooper minimum in Ar. We observe a few irregular features in the delay that may be signatures of resonances.

  • 29. Palmeri, Patrick
    et al.
    Quinet, Pascal
    Biémont, Emile
    Gurell, Jonas
    Stockholm University, Faculty of Science, Department of Physics.
    Lundin, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Norlin, Lars-Olov
    Royen, Peder
    Stockholm University, Faculty of Science, Department of Physics.
    Blagoev, Kiril
    Mannervik, Sven F.
    Stockholm University, Faculty of Science, Department of Physics.
    Lifetimes of metastable levels of singly ionized titanium : theory and experiment2008In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 41, no 12Article in journal (Refereed)
    Abstract [en]

    This paper presents new theoretical lifetimes of metastable levels in singly ionized titanium, Ti II. Along with the lifetimes, transition probabilities for several decay channels from these metastable levels are presented. The calculations are supported by experimental lifetime determinations of the 3d3 b 2D5/2 and 3d2(3P)4s b 2P3/2 levels along with revised values of the previously published lifetimes of the 3d2(3P)4s b 4P5/2 and 3d2(3P)4s b 2P1/2 levels originating partly from a reanalysis utilizing a recently developed method applied on the previously recorded data and partly from new measurements. The presented theoretical investigation of lifetimes of metastable levels in Ti II shows that the HFR calculations are in general compatible with measurements performed using the ion storage ring CRYRING of Stockholm University. The transition probabilities of forbidden lines derived from the new lifetime values will be useful for the diagnostics of low density laboratory or astrophysical plasmas, particularly those encountered in the strontium filament found in the ejecta of η Carinae.

  • 30. Paripas, B.
    et al.
    Palasthy, B.
    Vitez, G.
    Berenyi, Zoltan
    Stockholm University, Faculty of Science, Department of Physics.
    Post-collision interaction measured by coincidence spectrometry in the electron impact Auger process2008In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 41, no 3, p. 35201-Article in journal (Refereed)
    Abstract [en]

    Auger electron lineshapes after electron impact inner-shell ionization of argon at 500 eV primary electron energy are studied by the (e, 2e) coincidence technique. Emitted Auger electrons are detected in coincidence with the ionizing scattered electrons and the energy of the slow PCI inducer ejected electron is calculated from energy conservation. In particular, the strongly asymmetric energy sharing, and by this means the effect of the very low energy (i.e. 0-5 eV) ejected electrons, is measured and compared with calculations. The opposite case (equal energy sharing) is also studied.

  • 31.
    Pinheiro, Fernanda
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Universidade de Sao Paulo, Brazil.
    de Toledo Piza, A. F. R.
    Delocalization and superfluidity of ultracold bosonic atoms in a ring lattice2013In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 46, no 20, article id 205303Article in journal (Refereed)
    Abstract [en]

    Properties of bosonic atoms in small systems with a periodic quasi-one-dimensional circular toroidal lattice potential subjected to rotation are examined by performing the exact diagonalization in a truncated many-body space. The expansion of the many-body Hamiltonian is considered in terms of the first-band Bloch functions, and no assumption regarding restriction to nearest neighbour hopping (tight-binding approximation) is involved. A finite size version of the zero temperature phase diagrams of Fisher et al (1989 Phys. Rev. B 40 546570) is obtained and the results, in remarkable quantitative correspondence with the results available for larger systems, discussed. Ground-state properties relating to superfluidity are examined in the context of two-fluid phenomenology. The basic tool, consisting of the intrinsic inertia associated with small rotation angular velocities in the lab frame, is used to obtain the ground state 'superfluid fractions' numerically. They are analytically associated with one-body, uniform solenoidal currents in the case of the adopted geometry. These currents are in general incoherent superpositions of contributions from each eigenstates of the associated reduced one-body densities, with the corresponding occupation numbers as weights. Full coherence occurs therefore only when only one eigenstate is occupied by all bosons. The obtained numerical values for the superfluid fractions remain small throughout the parameter region corresponding to the 'Mott insulator to superfluid' transition, and saturate at unity only as the lattice is completely smoothed out.

  • 32.
    Polley, Debanjan
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Zhou Hagström, Nanna
    Stockholm University, Faculty of Science, Department of Physics. MBI Max-Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, Germany.
    von Korff Schmising, Clemens
    Eisebitt, Stefan
    Bonetti, Stefano
    Stockholm University, Faculty of Science, Department of Physics.
    Terahertz magnetic field enhancement in an asymmetric spiral metamaterial2018In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 51, no 22, article id 224001Article in journal (Refereed)
    Abstract [en]

    We use finite element simulations in both the frequency and the time-domain to study the terahertz resonance characteristics of a metamaterial (MM) comprising a spiral connected to a straight arm. The MM acts as a RLC circuit whose resonance frequency can be precisely tuned by varying the characteristic geometrical parameters of the spiral: inner and outer radius, width and number of turns. We provide a simple analytical model that uses these geometrical parameters as input to give accurate estimates of the resonance frequency. Finite element simulations show that linearly polarized terahertz radiation efficiently couples to the MM thanks to the straight arm, inducing a current in the spiral, which in turn induces a resonant magnetic field enhancement at the center of the spiral. We observe a large (approximately 40 times) and uniform (over an area of similar to 10 mu m(2)) enhancement of the magnetic field for narrowband terahertz radiation with frequency matching the resonance frequency of the MM. When a broadband, single-cycle terahertz pulse propagates towards the MM, the peak magnetic field of the resulting band-passed waveform still maintains a six-fold enhancement compared to the peak impinging field. Using existing laser-based terahertz sources, our MM design allows to generate magnetic fields of the order of 2 T over a time scale of several picoseconds, enabling the investigation of nonlinear ultrafast spin dynamics in table-top experiments. Furthermore, our MM can be implemented to generate intense near-field narrowband, multi-cycle electromagnetic fields to study generic ultrafast resonant terahertz dynamics in condensed matter.

  • 33. Reitsma, G.
    et al.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Boschman, L.
    Bodewits, E.
    Hoekstra, R.
    Schlatholter, T.
    Ion-polycyclic aromatic hydrocarbon collisions: kinetic energy releases for specific fragmentation channels2013In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 46, no 24, p. 245201-Article in journal (Refereed)
    Abstract [en]

    We report on 30 keV He2+ collisions with naphthalene (C10H8) molecules, which leads to very extensive fragmentation. To unravel such complex fragmentation patterns, we designed and constructed an experimental setup, which allows for the determination of the full momentum vector by measuring charged collision products in coincidence in a recoil ion momentum spectrometer type of detection scheme. The determination of fragment kinetic energies is found to be considerably more accurate than for the case of mere coincidence time-of-flight spectrometers. In fission reactions involving two cationic fragments, typically kinetic energy releases of 2-3 eV are observed. The results are interpreted by means of density functional theory calculations of the reverse barriers. It is concluded that naphthalene fragmentation by collisions with keV ions clearly is much more violent than the corresponding photofragmentation with energetic photons. The ion-induced naphthalene fragmentation provides a feedstock of various small hydrocarbonic species of different charge states and kinetic energy, which could influence several molecule formation processes in the cold interstellar medium and facilitates growth of small hydrocarbon species on pre-existing polycyclic aromatic hydrocarbons.

  • 34. Reitsma, G.
    et al.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Martin, S.
    Bredy, R.
    Chen, L.
    Bernard, J.
    Hoekstra, R.
    Schlatholter, T.
    Activation energies for fragmentation channels of anthracene dications experiment and theory2012In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 45, no 21, p. 215201-Article in journal (Refereed)
    Abstract [en]

    We have studied the fragmentation of the polycyclic aromatic hydrocarbon anthracene (C14H10) after double electron transfer to a 5 keV proton. The excitation energies leading to the most relevant dissociation and fission channels of the resulting molecular dication were directly determined experimentally. Density functional theory calculations were performed to explore the potential energy surfaces on which the fragmentation dynamics proceed. There is clear experimental evidence for a dominance of fission into C11H7+-C3H3+ over C2H2+ loss. The energetic ordering of the dissociation and fission channels and the kinetic energy releases are in good agreement with the theoretical results. It can be concluded that the unique combination of experiment and theory presented here is an excellent tool to study the fragmentation of complex molecular ions in unprecedented detail.

  • 35. Santos, L. O.
    et al.
    Rocha, A. B.
    Nascimento, Rodrigo F.
    Stockholm University, Faculty of Science, Department of Physics. UnED Petrópolis, Brazil.
    de Castro Faria, N. V.
    Jalbert, Ginette
    Potential energy curves and generalized oscillator strength for doubly excited states of hydrogen molecule2015In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 48, no 18, article id 185104Article in journal (Refereed)
    Abstract [en]

    We report calculations of potential energy curves for doubly excited states of the H-2 molecule in the 1.2a. u. <= R <= 12a. u. range at the multireference configuration interaction (MRCI) level based on multiconfigurational self-consistent field (MCSCF) orbitals. We focus on the Q(2) states which lie between the second and third ionization thresholds of the H-2(+) molecular ion, i.e. the (2)Sigma(+)(u) and (2)Pi(u) states, respectively, and dissociate in the H(2l) + H(2l) channels. The MCSCF/ MRCI approach allows us to successfully identify the molecular optically forbidden Q(2) (1)Sigma(+)(g) state which dissociates into two H(2s) atoms. Generalized oscillator strength as a function of transferred momentum for three doubly excited states is also presented.

  • 36. Schulz, M.
    et al.
    Fischer, D.
    Stockholm University, Faculty of Science, Department of Physics.
    Ferger, T.
    Moshammer, R.
    Ullrich, J.
    Four-particle Dalitz plots to visualize atomic break-up processes2007In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 40, no 15, p. 3091-3099Article in journal (Refereed)
    Abstract [en]

    We introduce a new method to analyse four-body fragmentation processes, which is basically an extension of Dalitz plots commonly used in particle physics to analyse three-body fragmentation processes. It enables for the first time the presentation of multiple differential cross sections as a function of all four fragments without loss of any part of the total cross section in the integral spectrum. As a first example, the technique is applied to ionization processes in atomic collisions.

  • 37.
    Shilyaeva, Ksenia
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Yarevsky, Evgeny
    St. Petersburg State University.
    Elander, Nils
    Stockholm University, Faculty of Science, Department of Physics.
    Identifying resonance structures in a scattering cross section using the N3+ + H -> NH3+ -> N2+ + H+ reaction as an example2009In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 42, no 4, p. 044011-Article in journal (Refereed)
  • 38. Sun, Ruirui
    et al.
    Meng, Qinghui
    Wang, Ming
    Fei, Weifei
    Zhang, Yanmei
    Chen, Jun
    Fang, Wenzheng
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. University of Science and Technology of China, People´s Republic of China.
    Shan, Xiaobin
    Liu, Fuyi
    Sheng, Liusi
    Experimental and theoretical study on the dissociative photoionization of methyl methacrylate2017In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 50, no 23, article id 235101Article in journal (Refereed)
    Abstract [en]

    The photoionization of methyl methacrylate and dissociation of its cation have been investigated by tunable vacuum ultraviolet synchrotron radiation coupled with time-of-flight mass spectrometer in the photon energy region of 9.0-15.5 eV. The ionization energy of methyl methacrylate and the appearance energies (AEs) for major fragments, C5H7O2+, C5H6O+, C4H5O2+,C4H5O+, C3H3O+ (C4H7+), C3H5+, C3H4+, C2H3O2+, and CH3+ are determined to be 9.76, 10.30, 10.66, 10.51, 11.17, 10.51, 10.74, 12.88, 12.73, 12.52, and 12.82 eV, respectively, by measurement of the photoionization efficiency curves. Possible formation pathways of the major fragments are proposed based on comparison of experimental AEs and energies predicted by ab initio G3B3 calculations. Transition states and intermediates involved in the dissociation channels are also located. The majority of the proposed channels occur through isomerization prior to dissociation. Hydrogen shift and ring closing/opening are found to be the dominant processes during photofragmentaion of methyl methacrylate.

  • 39.
    Sörngård, Johanna
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Dahlström, J. M.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Study of the possibilities with combinations of circularly and linearly polarized light for attosecond delay investigations2020In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 53, no 13, article id 134003Article in journal (Refereed)
    Abstract [en]

    We present calculations on the atomic delay in photoionzation obtained with different combinations of linearly and circularly polarized light, and show how a tensor operator approach can be used to readily obtain results for any combination from a single calculation of the radial integrals. We find that for certain choices of polarization and detection geometry a single time-delay measurement is enough to extract the atomic delay since the relative phase in a RABBIT type measurement will be imprinted on the photo electron anisotropy. We show further that the full angular dependence can be qualitatively understood from a plane wave analysis. The results are illustrated by many-body calculations of two-photon above threshold ionization on argon.

  • 40.
    Tempest, Kajsa-My
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    The Faddeev and Schrödinger approaches to Efimov states — a numerical comparison2023In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 56, no 20, article id 205301Article in journal (Refereed)
    Abstract [en]

    We compare effective hyperspherical three-body potentials calculated using the S-wave part of the Faddeev equations to calculations using the full Schrödinger equation. As two-body model potential we test both a short-range potential and a Lennard-Jones potential with van der Waals tail. In the former case we find excellent agreement between the two methods for the lowest adiabatic state, indicating that the Faddeev method can be a useful tool also for numerical computations. For excited states the two methods show important differences, but agree for hyperradii larger than about five times the range of the potential (independent of the value of the scattering length and of the number of bound states). For the van der Waals potential, we focus on how well the Faddeev method reproduces the so-called van der Waals universality. We find that indeed the universality is manifest also using this method, but at a slightly different value of the universal parameter κ*. We further derive an efficient method to solve the integro-differential equation arising in the Faddeev method.

  • 41.
    Umair, Muhammad
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    A search for resonances in the p mu e system2014In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 47, no 17, article id 175003Article in journal (Refereed)
    Abstract [en]

    The charge radius of the proton has recently been determined from 2s-2p spectroscopy of muonic hydrogen, giving a result which significantly deviates from earlier measurements. One hypothesis is that this discrepancy could arise because a metastable p mu e state is formed under the p mu (2s) threshold. We search for such a state by considering the three-body pex and p mu x systems, where x is a particle with charge -e and a mass which is varied between the electron and muon mass. We identify a new class of resonances, which extends the mass range allowing formation of resonances compared to an earlier work. We conclude that no p mu e resonances relevant for 2s-2p spectroscopy in muonic hydrogen can exist.

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  • 42.
    Umair, Muhammad
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Natural and unnatural parity resonance states in positron-hydrogen scattering2014In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 47, no 22, article id 225001Article in journal (Refereed)
    Abstract [en]

    We present an investigation of resonances with natural and unnatural parities in positron scattering with atomic hydrogen. The complex scaling method has been used. Resonance states for natural parity pi=(-1)(J) with total angular momenta J = 0 - 2 and unnatural parity pi = (-1)(J+1) with J = 1, 2 are calculated. Resonance energies and widths are reported and compared with other theoretical calculations.

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  • 43.
    Umair, Muhammad
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Positronium-dipole induced resonances in e$^{+}$-H and e$^{+}$-alkali systemsIn: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455Article in journal (Refereed)
  • 44.
    Umair, Muhammad
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Positronium-dipole induced resonances in e(+)-H and e(+)-alkali systems2017In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 50, no 4, article id 044001Article in journal (Refereed)
    Abstract [en]

    We derive general universal scaling relations governing resonances induced by the dipole moment of excited positronium interacting with atomic ions. A single non-universal parameter, which contains all the system-dependent information, is defined. Our results are compared to numerical calculations, using complex scaling, for S, P, and D-wave resonances below the positronium n. =. 2 threshold in the e(+)-(H, Li, Na, K) systems. The energy and width ratios of the successive resonances are found to agree well with the analytically derived scaling law.

  • 45.
    Umair, Muhammad
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Resonances in positron-potassium ($e^{+}$-K) system with natural and unnatural parities2016In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 49, no 1, article id 015004Article in journal (Refereed)
    Abstract [en]

    We present an investigation of resonances with natural and unnatural parities in the positron-potassium system using the complex scaling method. A model potential is used to represent the interaction between the core and the valence electron. Explicitly correlated Gaussian wave functions are used to represent the correlation effects between the valence electron, the positron and the K+ core. Resonance energies and widths for two partial waves (S- and P-wave) below the K(4p, 5s, 5p, 4d, 4f) excitation thresholds and positronium n = 2 formation threshold are calculated for natural parity. Resonance states for P-e below the K(4d) excitation threshold and positronium n = 2, 3 formation thresholds are calculated for unnatural parity which has not been previously reported. Below both positronium thresholds we have found a dipole series of resonances, with binding energies scaling in good agreement with exceptions from an analytical calculation. The present results are compared with those in the literature.

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  • 46. Yamashita, Takuma
    et al.
    Umair, Muhammad
    Stockholm University, Faculty of Science, Department of Physics.
    Kino, Yasushi
    Bound and resonance states of positronic copper atoms2017In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 50, no 20, article id 205002Article in journal (Refereed)
    Abstract [en]

    We report a theoretical calculation for the bound and S-wave resonance states of the positronic copper atom (e(+) Cu). A positron is a positively charged particle; therefore, a positronic atom has an attractive correlation between the positron and electron. A Gaussian expansion method is adopted to directly describe this correlation as well as the strong repulsive interaction with the nucleus. The correlation between the positron and electron is much more important than that between electrons in an analogous system of Cu-, although the formation of a positronium (Ps) in e(+) Cu is not expressed in the ground state structure explicitly. Resonance states are calculated with a complex scaling method and identified above the first excited state of the copper atom. Resonance states below Ps (n = 2) + Cu+ classified to a dipole series show agreement with a simple analytical law. Comparison of the resonance energies and widths of e(+) Cu with those of e(+) K, of which the potential energy of the host atom resembles that of e(+) Cu, reveals that the positions of the resonance for the e(+) Cu dipole series deviate equally from those of e(+) K.

  • 47. Yang, B.
    et al.
    Novotny, O.
    Krantz, C.
    Buhr, H.
    Mendes, M.
    Nordhorn, C.
    Geppert, Wolf D.
    Stockholm University, Faculty of Science, Department of Physics.
    Grieser, M.
    Repnow, R.
    Berg, M.
    Bing, D.
    Domesle, C.
    Grussie, F.
    Savin, D. Wolf
    Schwalm, D.
    Cai, X.
    Wolf, A.
    Exploring high-energy doubly excited states of NH by dissociative recombination of NH+2014In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 47, no 3, p. 035201-Article in journal (Refereed)
    Abstract [en]

    We have investigated electron capture by NH+ resulting in dissociative recombination (DR). The impact energies studied of similar to 4-12 eV extend over the range below the two lowest predicted NH+ dissociative states in the Franck-Condon (FC) region of the ion. Our focus has been on the final state populations of the resulting N and H atoms. The neutral DR fragments are detected downstream of a merged electron and ion beam interaction zone in the TSR storage ring, which is located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. Transverse fragment distances were measured on a recently developed high count-rate imaging detector. The distance distributions enabled a detailed tracking of the final state populations as a function of the electron collision energy. These can be correlated with doubly excited neutral states in the FC region of the ion. At low electron energy of similar to 5 eV, the atomic product final levels are nitrogen Rydberg states together with ground-state hydrogen. In a small electron energy interval near 7 eV, a significant part of the final state population forms hydrogen Rydberg atoms with nitrogen atoms in the first excited (D-2) term, showing the effect of Rydberg doubly excited states below the predicted 2(2)Pi ionic potential. The distance distributions above similar to 10 eV are compatible with nitrogen Rydberg states correlating to the doubly excited Rydberg state manifold below the ionic 2(4) Sigma(-) level.

  • 48. Yarevsky, E.
    et al.
    Yakovlev, S. L.
    Elander, Nils
    Stockholm University, Faculty of Science, Department of Physics.
    Potential splitting approach to e-H and e-He+ scattering2017In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 50, no 5, article id 055001Article in journal (Refereed)
    Abstract [en]

    An approach based on splitting the reaction potential into a finite range part and a long range tail part to describe few-body scattering in the case of a Coulombic interaction is proposed. The solution to the Schrodinger equation for the long range tail of the reaction potential is used as an incoming wave. This reformulation of the scattering problem into an inhomogeneous Schrodinger equation with asymptotic outgoing waves makes it suitable for solving with the exterior complex scaling technique. The validity of the approach is analyzed from a formal point of view and demonstrated numerically, where the calculations are performed with the finite element method. The method of splitting the potential in this way is illustrated with calculations of the electron scattering on the hydrogen atom and the positive helium ion in energy regions where resonances appear.

  • 49. Yarevsky, E.
    et al.
    Yakovlev, S. L.
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    Elander, Nils
    Stockholm University, Faculty of Science, Department of Physics.
    Potential-splitting approach applied to the Temkin-Poet model for electron scattering off the hydrogen atom and the helium ion2015In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 48, no 11Article in journal (Refereed)
    Abstract [en]

    The study of scattering processes in few body systems is a difficult problem especially if long range interactions are involved. In order to solve such problems, we develop here a potential-splitting approach for three-body systems. This approach is based on splitting the reaction potential into a finite range core part and a long range tail part. The solution to the Schrodinger equation for the long range tail Hamiltonian is found analytically, and used as an incoming wave in the three body scattering problem. This reformulation of the scattering problem makes it suitable for treatment by the exterior complex scaling technique in the sense that the problem after the complex dilation is reduced to a boundary value problem with zero boundary conditions. We illustrate the method with calculations on the electron scattering off the hydrogen atom and the positive helium ion in the frame of the Temkin-Poet model.

  • 50. Zhaunerchyk, V.
    et al.
    Kamińska, Magdalena
    Stockholm University, Faculty of Science, Department of Physics. Uppsala University, Sweden; Jan Kochanowski University, Poland.
    Mucke, M.
    Squibb, R. J.
    Eland, J. H. D.
    Piancastelli, M. N.
    Frasinski, L. J.
    Grilj, J.
    Koch, M.
    McFarland, B. K.
    Sistrunk, E.
    Gühr, M.
    Coffee, R. N.
    Bostedt, C.
    Bozek, J. D.
    Salén, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Meulen, Peter v. d.
    Stockholm University, Faculty of Science, Department of Physics.
    Linusson, Per
    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.
    Richter, R.
    Prince, K. C.
    Takahashi, O.
    Osipov, T.
    Fang, L.
    Murphy, B. F.
    Berrah, N.
    Feifel, R.
    Disentangling formation of multiple-core holes in aminophenol molecules exposed to bright X-FEL radiation2015In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 48, no 24, article id 244003Article in journal (Refereed)
    Abstract [en]

    Competing multi-photon ionization processes, some leading to the formation of double core hole states, have been examined in 4-aminophenol. The experiments used the linac coherent light source (LCLS) x-ray free electron laser, in combination with a time-of-flight magnetic bottle electron spectrometer and the correlation analysis method of covariance mapping. The results imply that 4-aminophenol molecules exposed to the focused x-ray pulses of the LCLS sequentially absorb more than two x-ray photons, resulting in the formation of multiple core holes as well as in the sequential removal of photoelectrons and Auger electrons (so-called PAPA sequences).

12 1 - 50 of 51
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