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  • 1. Andersson, E.
    et al.
    Fritzsche, S.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Hedin, L.
    Eland, J. H. D.
    Rubensson, J. -E
    Karlsson, L.
    Feifel, R.
    Multielectron coincidence study of the double Auger decay of 3d-ionized krypton2010Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 82, nr 4, s. 043418-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Multielectron coincidence data for triple ionization of krypton have been recorded above the 3d ionization threshold at two photon energies (140 and 150 eV). Three principal transition pathways have been observed, two involving double Auger transitions from Kr+, and one involving single Auger transitions from Kr2+ created by direct single-photon double ionization. The decay of the 3d(9) D-2(5/2,3/2) states in Kr+ has been analyzed in some detail and is found to be strongly dominated by cascade processes where two electrons with well-defined energies are emitted. The decay paths leading to the 4s(2)4p(3) S-4, D-2, and P-2 states of Kr3+ are analyzed and energies of seven intermediate states in Kr2+ are given. A preliminary investigation of the decay paths from Kr+ 3d (9)4p(5)nl shake-up states has also been carried out.

  • 2. Andersson, E.
    et al.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Fritzsche, S.
    Hedin, L.
    Eland, J. H. D.
    Karlsson, L.
    Rubensson, J. -E
    Feifel, R.
    Formation of Kr3+ via core-valence doubly ionized intermediate states2012Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 85, nr 3, s. 032502-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The time-of-flight photoelectron-photoion coincidence technique has been used to study single-photon 3d(9)4p(5) core-valence double ionization of Kr and subsequent Auger decay to triply charged states associated with the 4s(2)4p(3) and 4s(1)4p(4) configurations. The photon energy used was h nu = 150 eV. Multiconfiguration Dirac-Fock calculations were performed both for the doubly ionized intermediate states and the triply ionized final states. The intermediate states of Kr2+ are observed between 120 and 125 eV, whereas the final states of Kr3+ are observed between 74- and 120-eV ionization energy. Assignments of all structures are made based on the present numerical results. The calculated Auger rates give a detailed explanation of the relative line strengths observed.

  • 3. Andersson, E.
    et al.
    Niskanen, J.
    Hedin, L.
    Eland, J. H. D.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Karlsson, L.
    Rubensson, J. -E
    Carravetta, V.
    Agren, H.
    Feifel, R.
    Core-valence double photoionization of the CS2 molecule2010Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 133, nr 9, s. 94305-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Double photoionization spectra of the CS2 molecule have been recorded using the TOF-PEPECO technique in combination with synchrotron radiation at the photon energies h nu=220, 230, 240, 243, and 362.7 eV. The spectra were recorded in the S 2p and C 1s inner-shell ionization regions and reflect dicationic states formed out of one inner-shell vacancy and one vacancy in the valence region. MCSCF calculations were performed to model the energies of the dicationic states. The spectra associated with a S 2p vacancy are well structured and have been interpreted in some detail by comparison to conventional S 2p and valence photoelectron spectra. The lowest inner-shell-valence dicationic state is observed at the vertical double ionization energy 188.45 eV and is associated with a (2p(3/2))(-1)(2 pi(g))(-1) double vacancy. The spectrum connected to the C 1s vacancy shows a distinct line at 310.8 eV, accompanied by additional broad features at higher double ionization energies. This line is associated with a (C 1s)(-1)(2 pi(g))(-1) double vacancy. (C-) 2010 American Institute of Physics. [doi: 10.1063/1.3469812]

  • 4. Andersson, J.
    et al.
    Beerwerth, R.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Eland, J. H. D.
    Zhaunerchyk, V.
    Fritzsche, S.
    Feifel, R.
    Triple ionization of atomic Cd involving 4p(-1) and 4s(-1) inner-shell holes2015Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 92, nr 2, artikel-id 023414Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The triple ionization spectrum of atomic Cd formed upon the removal of a 4p or a 4s inner-shell electron and subsequent Auger decays has been obtained at 200 eV photon energy. By using a versatile multielectron coincidence detection technique based on a magnetic bottle spectrometer in combination with multiconfiguration Dirac-Fock calculations, Auger cascades leading to tricationic final states have been analyzed and final-state configurations have been identified. The most prominent Auger cascades leading to the ground state of Cd3+ have been identified in good agreement with theory.

  • 5. Eland, J. H. D.
    et al.
    Andric, L.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Hedin, L.
    Plogmaker, S.
    Palaudoux, J.
    Penent, F.
    Lablanquie, P.
    Feifel, R.
    Triple ionization of CO(2) by valence and inner shell photoionization2011Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 135, nr 13, s. 134309-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Spectra of triply ionized CO(2) have been obtained from photoionization of the molecule using soft x-ray synchrotron light and an efficient multi-electron coincidence technique. Although all states of the CO(2)(+++) trication are unstable, the ionization energy for formation of molecular ions at a geometry similar to that of the neutral molecule is determined as 74 +/- 0.5 eV.

  • 6. Eland, J. H. D.
    et al.
    Fink, R. F.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Hedin, L.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Plogmaker, S.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Feifel, Raimund
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Single and multiple photoionisation of H(2)S by 40-250 eV photons2011Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, nr 41, s. 18428-18435Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Multi-electron coincidence measurements on photoionisation of H(2)S have been carried out at photon energies from 40 to 250 eV. They quantify molecular field effects on the Auger process in detail and are in good agreement with the existing theory. Spectra of core-valence double ionisation of H(2)S are presented and partially analysed. Auger decays from the core-valence states produce triply charged product spectra with unexplained and surprising intensity distributions. Triple ionisation by the double Auger process from 2p hole states shows little effect of the molecular field splitting, but includes a substantial contribution from cascade processes, some involving dissociation in intermediate states. The onset of triple ionisation at the molecular geometry is determined as 61 +/- 0.5 eV.

  • 7. Eland, J. H. D.
    et al.
    Hochlaf, M.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Andersson, E.
    Hedin, L.
    Feifel, R.
    Triple ionization spectra by coincidence measurements of double Auger decay: The case of OCS2010Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 132, nr 1, s. 14311-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    By combining multiple electron coincidence detection with ionization by synchrotron radiation, we have obtained resolved spectra of the OCS3+ ion created through the double Auger effect. The form of the spectra depends critically on the identity of the atom bearing the initial hole. High and intermediate level electron structure calculations lead to an assignment of the resolved spectrum from ionization via the S 2p hole. From the analysis it appears that the double Auger effect from closed shell molecules favors formation of doublet states over quartet states. Molecular field effects in the double Auger effect are similar to those in the single Auger effect in linear molecules.

  • 8. Eland, J. H. D.
    et al.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Hedin, L.
    Andersson, E.
    Rubensson, J. -E
    Feifel, R.
    Coincidence technique using synchrotron radiation for triple photoionization: Results on rare gas atoms2008Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 78, nr 6, s. 63423-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Final-state trication spectra and electron distributions produced by soft x-ray single-photon triple ionization of rare gas atoms have been obtained by a multiple-coincidence technique using storage-ring synchrotron radiation. The technique uses electron time of flight with ion detection to overcome the problem of high repetition rates in single-bunch operation. A correction needed to the triple-ionization energy of Kr currently listed in standard tables is confirmed, and the method's ability to examine the three-electron distributions, characterizing the ionization mechanisms and post-collision interactions, is illustrated.

  • 9. Eland, J. H. D.
    et al.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Hedin, L.
    Andersson, E.
    Rubensson, J-E
    Feifel, R.
    Triple ionisation of methane by double Auger and related pathways2010Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 485, nr 03-jan, s. 21-25Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Triple ionisation of methane by decay of the singly charged ion with a 1s vacancy produces a trication spectrum starting near 70 eV binding energy. Vibrational excitation in the initial hole state broadens and shifts the triple ionisation bands. Ionisation through core-valence doubly ionised states gives lower triple ionisation onsets and changes the spectral intensity pattern in accordance with retention of the initial valence holes in course of the double Auger effect. The double Auger effects occur both directly and as cascades, the different pathways producing different electron distributions and final state spectra.

  • 10. Eland, J. H. D.
    et al.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Mucke, M.
    Feifel, R.
    Homonuclear site-specific photochemistry by an ion-electron multi-coincidence spectroscopy technique2012Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 548, s. 90-94Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    By combining multi-particle coincidence detection of electrons and ions with ionisation by soft X-ray synchrotron radiation we demonstrate an effective tool for atomic spectroscopy and site-specific photochemistry. Its most novel capability is application to molecular fragmentation after K-shell vacancy production in atoms distinguished only by their chemical environment.

  • 11. Eland, J. H. D.
    et al.
    Rigby, C. F.
    Andersson, E.
    Palaudoux, J.
    Andric, L.
    Penent, F.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Hedin, L.
    Karlsson, L.
    Rubensson, J. -E
    Hikosaka, Y.
    Ito, K.
    Lablanquie, P.
    Feifel, R.
    Spectra of the triply charged ion CS23+ and selectivity in molecular Auger effects2010Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 132, nr 10, s. 104311-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Spectra of triply charged carbon disulphide have been obtained by measuring, in coincidence, all three electrons ejected in its formation by photoionization. Measurements of the CS23+ ion in coincidence with the three electrons identify the energy range where stable trications are formed. A sharp peak in this energy range is identified as the (2)Pi ground state at 53.1 +/- 0.1 eV, which is the lowest electronic state according to ab initio molecular orbital calculations. Triple ionization by the double Auger effect is provisionally divided, on the basis of the pattern of energy sharing between the two Auger electrons into contributions from direct and cascade Auger processes. The spectra from the direct double Auger effect via S 2p, S 2s, and C 1s hole states contain several resolved features and show selectivity based on the initial charge localization and on the identity of the initial state. Triple ionization spectra from single Auger decay of S 2p-based core-valence states CS22+ show retention of the valence holes in this Auger process. Related ion-electron coincidence measurements give the triple ionization yields and the breakdown patterns in triple photoionization at selected photon energies from 90 eV to above the inner shell edges.

  • 12. Eland, J. H. D.
    et al.
    Squibb, R. J.
    Mucke, M.
    Zagorodskikh, S.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Feifel, R.
    Direct observation of three-electron collective decay in a resonant Auger process2015Ingår i: New Journal of Physics, E-ISSN 1367-2630, Vol. 17, artikel-id 122001Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using a multi-electron coincidence technique combined with synchrotron radiation we demonstrate the real existence of the elusive three-electron collective process in resonant Auger decay of Kr. The three-electron process is about 40 times weaker than the competing two-electron processes.

  • 13. Eland, J. H. D.
    et al.
    Tashiro, M.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Ehara, M.
    Ueda, K.
    Feifel, R.
    Double Core Hole Creation and Subsequent Auger Decay in NH3 and CH4 Molecules2010Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 105, nr 21, s. 213005-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Energies of the hollow molecules CH42+ and NH32+ with double vacancies in the 1s shells have been measured using an efficient coincidence technique combined with synchrotron radiation. The energies of these states have been determined accurately by high level electronic structure calculations and can be well understood on the basis of a simple theoretical model. Their major decay pathway, successive Auger emissions, leads first to a new form of triply charged ion with a core hole and two valence vacancies; experimental evidence for such a state is presented with its theoretical interpretation. Preedge 2-hole-1-particle (2h-1p) states at energies below the double core-hole states are located in the same experiments and their decay pathways are also identified.

  • 14.
    Elshakre, M.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Storchi, L.
    Kloda, Tomasz
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Heijkenskjold, F.
    Gengelbach, A.
    Karlsson, L.
    Hansson, Tony
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Tarantelli, F.
    Feifel, R.
    A photoelectron and double photoionization study of the valence electronic structure of 1,4-bromofluorobenzene2009Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 131, nr 18, s. 184302-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Conventional photoelectron and time-of-flight photoelectron-photoelectron coincidence (TOF-PEPECO) spectra have been measured for the outer valence region of the 1,4-bromofluorobenzene molecule. The photoelectron spectra were recorded using Hela radiation from a resonance Source, and the TOF-PEPECO spectra were recorded using HeII alpha radiation from a pulsed resonance source. The former provide energies of the cationic states and the latter of the dicationic states. The spectra are adequately interpreted with the aid of accurate Green's function calculations, showing very significant correlation effects. The lowest double ionization energy is found at 23.45 eV associated with the (4b(1))X-2 (1)A(1) dicationic state.

  • 15. Feifel, Raimund
    et al.
    Eland, John H. D.
    Squibb, Richard J.
    Mucke, Melanie
    Zagorodskikh, Sergey
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Tarantelli, Francesco
    Kolorenc, Premysl
    Averbukh, Vitali
    Ultrafast Molecular Three-Electron Auger Decay2016Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 116, nr 7, artikel-id 073001Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Three-electron Auger decay is an exotic and elusive process, in which two outer-shell electrons simultaneously refill an inner-shell double vacancy with emission of a single Auger electron. Such transitions are forbidden by the many-electron selection rules, normally making their decay lifetimes orders of magnitude longer than the few-femtosecond lifetimes of normal (two-electron) Auger decay. Here we present theoretical predictions and direct experimental evidence for a few-femtosecond three-electron Auger decay of a double inner-valence-hole state in CH3F. Our analysis shows that in contrast to double core holes, double inner-valence vacancies in molecules can decay exclusively by this ultrafast threeelectron Auger process, and we predict that this phenomenon occurs widely.

  • 16. Frasinski, L. J.
    et al.
    Zhaunerchyk, V.
    Mucke, M.
    Squibb, R. J.
    Siano, M.
    Eland, J. H. D.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    van der Meulen, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Sahlén, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Thomas, Richard
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Larsson, Mats
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    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 Mapping2013Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 111, nr 7, s. 073002-Artikel i tidskrift (Refereegranskat)
    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.

  • 17. Hedin, L.
    et al.
    Tashiro, M.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Eland, J. H. D.
    Ehara, M.
    Ueda, K.
    Zhaunerchyk, V.
    Karlsson, L.
    Feifel, R.
    Single site double core level ionisation of OCS2014Ingår i: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 439, s. 111-116Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Single site O1s, C1s and S2p double ionisation of the OCS molecule has been investigated using a magnetic bottle multi-electron coincidence time-of-flight spectrometer. Photon energies of 1300, 750 and 520 eV, respectively, were used for the ionisation, and spectra were obtained from which the double core ionisation energies could be determined. The energies measured for 1s double ionisation are 1172 eV (O1s(-2)) and 659 eV (C1s(-2)). For the S2p double ionisation three dicationic states are expected, P-3, D-1 and S-1. The ionisation energies obtained for these states are 373 eV (P-3), 380 eV (D-1) and 388 eV (S-1). The ratio between the double and single core ionisation energies are in all cases equal or close to 2.20. Auger spectra of OCS, associated with the O1s(-2), C1s(-2) and S2p(-2) dicationic states, were also recorded incorporating both electrons emitted as a result of the filling of the two core vacancies. As for other small molecules, the spectra show an atomic-like character with Auger bands located in the range 480-560 eV for oxygen, 235-295 eV for carbon and 100-160 eV for sulphur. The interpretation of the spectra is supported by CASSCF and CASCI calculations. The cross section ratio between double and single core hole creation was estimated as 3.7 x 10(-4) for oxygen at 1300 eV, 3.7 x 10(-4) for carbon at 750 eV and as 2.2 x 10(-3) for sulphur at 520 eV.

  • 18. Hedin, L.
    et al.
    Tashiro, M.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Eland, J. H. D.
    Ehara, M.
    Ueda, K.
    Zhaunerchyk, V.
    Karlsson, L.
    Pernestal, K.
    Feifel, R.
    N1s and O1s double ionization of the NO and N2O molecules2014Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 140, nr 4, s. 044309-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Single-site N1s and O1s double core ionisation of the NO and N2O molecules has been studied using a magnetic bottle many-electron coincidence time-of-flight spectrometer at photon energies of 1100 eV and 1300 eV. The double core hole energies obtained for NO are 904.8 eV (N1s(-2)) and 1179.4 eV (O1s(-2)). The corresponding energies obtained for N2O are 896.9 eV (terminal N1s(-2)), 906.5 eV (central N1s(-2)), and 1174.1 eV (O1s(-2)). The ratio between the double and single ionisation energies are in all cases close or equal to 2.20. Large chemical shifts are observed in some cases which suggest that reorganisation of the electrons upon the double ionization is significant. Delta-self-consistent field and complete active space self-consistent field (CASSCF) calculations were performed for both molecules and they are in good agreement with these results. Auger spectra of N2O, associated with the decay of the terminal and central N1s(-2) as well as with the O1s(-2) dicationic states, were extracted showing the two electrons emitted as a result of filling the double core holes. The spectra, which are interpreted using CASSCF and complete active space configuration interaction calculations, show atomic-like character. The cross section ratio between double and single core hole creation was estimated as 1.6 x 10(-3) for nitrogen at 1100 eV and as 1.3 x 10(-3) for oxygen at 1300 eV.

  • 19.
    Kloda, Tomasz
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Matsuda, Akitaka
    Karlsson, Hans O.
    Elshakre, Mohamed
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Eland, John H. D.
    Feifel, Raimund
    Hansson, Tony
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Strong-field photoionization of O-2 at intermediate light intensity2010Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 82, nr 3, s. 33431-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigated by electron spectroscopy the strong-field multiphoton ionization of O-2 molecules with ultrashort laser pulses in the intensity range between the multiphoton and tunneling regimes. The ionization proceeds by at least three different mechanisms, in addition to the eight- and nine-photon nonresonant pathways. Transient multiphoton resonances with vibrational Rydberg levels give rise to direct Freeman-type peaks with sublaser linewidth and spin-orbit splitting. Some resonance levels actually become populated and yield extremely narrow lines because of postpulse vibrational autoionization. When the lowest photon order resonance channel for the Rydberg states is closed, a third contribution becomes dominant with a main peak at 0.4 eV that shares its main properties with the recently discovered universal low-energy structure in the electron spectra of atoms and molecules [C. I. Blaga et al., Nat. Phys. 5, 335 (2009); W. Quan et al., Phys. Rev. Lett. 103, 093001 (2009)]. The variation of the Freeman resonance spectrum with the laser peak intensity is well correlated with the vibronic Franck-Condon factors for the overlap of the intermediate Rydberg state with the O-2 ground state. Accordingly, the Freeman peaks could be unambiguously assigned to individual vibronic multiphoton resonances, and the disappearance of the Freeman resonances at a certain laser intensity could be explained. The population of the autoionizing Rydberg states could be assigned similarly to such vibronic resonances.

  • 20.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Single-photon multiple ionization processes studied by electron coincidence spectroscopy2013Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis is based on studies of multiple ionization of atoms and molecules induced by the absorption of a single photon. For the experimental investigations a time-of-flight magnetic bottle spectrometer has been used to detect the emitted electrons in coincidence. The method of coincidence time-of-flight spectroscopy and the experimental setup used is described. Experimental and theoretical results on molecular double core holes (DCHs) and multiple ionization of atoms are presented.

    Molecular DCHs are of considerable interest, as their chemical shifts are predicted to be more sensitive than their single core hole counterparts. Using CH4 and NH3 as examples, it is shown that molecules with two vacancies in the innermost shell can be studied using synchrotron light in combination with our coincidence technique. The chemical shifts of S 2p DCHs are investigated for the molecules CS2, H2S and SO2 and the influence of relaxation effects on the shifts are estimated. In the studies of atoms, the main focus is on the processes leading to double and higher degrees of ionization, and the final state populations. In cadmium double photoionization in the photon energy region 40-200 eV occurs mainly by indirect ionization via valence ionized satellite states and through Coster-Kronig decay of inner shell hole states. In valence-valence ionization of krypton by 88 eV photons both direct and indirect ionization processes are found to be important. For the indirect pathways strong final state selectivity in the autoionization decays of the intermediate states is observed. Triple ionization of krypton via intermediate core-valence doubly ionized states is investigated. The intermediate states are observed in the energy region 120-125 eV, and their decay to states of the triply charged ion is mapped. Experimental and theoretical results on the formation of 2p double hole states in argon are presented.

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  • 21.
    Linusson, Per
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Fritzsche, S.
    Eland, J. H. D.
    Hedin, L.
    Karlsson, L.
    Feifel, R.
    Double ionization of atomic cadmium2011Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 83, nr 2, s. 023424-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have recorded the double photoionization spectrum of atomic Cd at four different photon energies in the range 40-200 eV. The main channel is single ionization and subsequent decay of excited Cd(+) states, some involving Coster-Kronig processes, whereas direct double ionization is found to be weak. The decay of the excited Cd(+) states shows a strong selectivity, related to the configuration of the final state. Double ionization leading to the Cd(2+) ground state is investigated in some detail and is found to proceed mainly through ionization and decay of 4d correlation satellites. The most prominent autoionization peaks have been identified with the aid of quantum-mechanical calculations.

  • 22.
    Linusson, Per
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Fritzsche, S.
    Eland, J. H. D.
    Mucke, M.
    Feifel, R.
    Single-photon multiple ionization forming double vacancies in the 2p subshell of argon2013Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 87, nr 4, s. 043409-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Single-photon ionization leading to two vacancies in the 2p subshell of argon is investigated experimentally using the photoelectron time-of-flight magnetic bottle coincidence technique. Three peaks corresponding to the 3P, 1D, and 1S states of the dication are found in the ionization energy range 535 to 562 eV. Multiconfigurational Dirac-Fock calculations were performed to estimate the single-photon double-ionization cross sections. Reasonable agreement between the measured and simulated spectra is found if single and double excitations are taken into account in the wave-function expansion.

  • 23.
    Linusson, Per
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Hedin, L.
    Eland, J. H. D.
    Squibb, R. J.
    Mucke, M.
    Zagorodskikh, S.
    Karlsson, L.
    Feifel, R.
    Complete double valence photoionization study of the electron spectra of krypton2013Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 88, nr 2, s. 022510-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Double photoionization spectra of Kr have been recorded using monochromatized synchrotron radiation of 88 eV photon energy and a versatile multielectron coincidence time-of-flight spectroscopy technique. The formation of the Kr2+ states of the lowest-energy configuration 4s(2)4p(4) is partly direct, producing electron pairs with a continuous distribution, and partly indirect via superexcited singly ionized states. The superexcited Kr+ states show strong and hitherto unexplained selectivity in branching to final Kr2+ states. Kr2+ states based on excited configurations are formed mainly by direct double photoionization.

  • 24.
    Linusson, Per
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Hedin, L.
    Eland, J. H. D.
    Squibb, R.
    Mucke, M.
    Zagorodskikh, S.
    Karlsson, L.
    Feifel, R.
    A complete double valence photoionization study of the electron spectra of kryptonManuskript (preprint) (Övrigt vetenskapligt)
  • 25.
    Linusson, Per
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Stenrup, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Larson, Åsa
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Andersson, E.
    Heijkenskjold, F.
    Andersson, P.
    Eland, J. H. D.
    Karlsson, L.
    Rubensson, J. -E
    Feifel, R.
    Double photoionization of alcohol molecules2009Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 80, nr 3, s. 32516-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The double valence photoionization spectra of methanol, ethanol, and n-propyl alcohol have been recorded using a time-of-flight photoelectron-photoelectron coincidence technique. The spectra show a well-defined onset followed by broad rounded bands. The lowest vertical double ionization energies have been determined for all molecules and are found to be 32.1, 29.6, and 28.2 eV, respectively. These energies have been applied along with single ionization energies from conventional photoelectron spectra to investigate a recently derived rule of thumb for determination of the lowest double ionization energy in molecules. Many-electron ab initio calculations have been performed on the dicationic ground states in good agreement with the experimental values. For methanol, also excited dicationic states have been calculated up to about 40 eV and used for a detailed interpretation of the experimental spectrum.

  • 26.
    Linusson, Per
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Storchi, L.
    Heijkenskjold, F.
    Andersson, E.
    Elshakre, M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Pfeifer, B.
    Colombet, Meryll
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Eland, J. H. D.
    Karlsson, L.
    Rubensson, J. -E
    Tarantelli, F.
    Feifel, R.
    Double photoionization of thiophene and bromine-substituted thiophenes2008Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 129, nr 23, s. 234303-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report the double photoionization spectra of thiophene, 3-bromothiophene, and 3,4-dibromothiophene using a coincidence spectroscopy technique based on electron time-of-flight measurements. Spectra have been recorded between the onset and 40.814 eV using He II alpha radiation. The He I photoelectron spectrum of 3,4-dibromothiophene has also been measured. All the spectra have been analyzed and interpreted in detail on the basis of theoretical simulations from accurate Green's function calculations.

  • 27.
    Linusson, Per
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Takahashi, O.
    Ueda, K.
    Eland, J. H. D.
    Feifel, R.
    Structure sensitivity of double inner-shell holes in sulfur-containing molecules2011Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 83, nr 2, s. 022506-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To demonstrate the structure sensitivity of double inner-shell hole spectroscopy, we have measured energies of H(2)S(2+), SO(2)(2+), and CS(2)(2+) with the two vacancies in the sulfur 2p shell using a multielectron coincidence technique combined with synchrotron radiation. We describe how to extract intrinsic chemical information which is masked by the orbital relaxation effect in conventional core-level photoelectron spectroscopy.

  • 28. Mucke, M.
    et al.
    Eland, J. H. D.
    Takahashi, O.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Lebrun, D.
    Ueda, K.
    Feifel, R.
    Formation and decay of core-orbital vacancies in the water molecule2013Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 558, s. 82-87Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Primary steps in the interaction of high energy photons with water creating multiply ionised products are examined experimentally and theoretically. Double Auger decay from a 1s-hole state populates triply ionised states between 80 and 140 eV binding energy. Ejection of one 1s electron and one valence electron gives states around 570 eV which decay to triply ionised states between 75 and 110 eV. Nuclear motion in these states competes with Auger decay and substantially modifies the final state spectra. The double core-hole state from ionisation of both 1s electrons is found at 1171 +/- 1 eV and calculated at 1170.85 eV.

  • 29. Mucke, M.
    et al.
    Zhaunerchyk, Vitali
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Uppsala University, Sweden; University of Gothenburg, Sweden.
    Frasinski, L. J.
    Squibb, R. J.
    Siano, M.
    Eland, J. H. D.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Salén, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    vab der Meulen, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Thomas, Richard D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Larsson, Mats
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    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 laser2015Ingår i: New Journal of Physics, E-ISSN 1367-2630, Vol. 17, artikel-id 073002Artikel i tidskrift (Refereegranskat)
    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.

  • 30. Niskanen, J.
    et al.
    Andersson, E.
    Eland, J. H. D.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Hedin, L.
    Karlsson, L.
    Feifel, R.
    Vahtras, O.
    Symmetry breaking in core-valence double photoionization of SO22012Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 85, nr 2, s. 023408-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Core-valence double photoionization electron spectra of the SO2 molecule involving the S 2p and O 1s inner shells have been measured using a time-of-flight multiparticle coincidence technique. The experimental spectra are compared with quantum-chemical calculations based on density functional theory by which several core-valence dicationic states are identified. Assignments conform with a picture where the formation of a O 1s-valence dicationic state is associated with a physical, pseudo-Jahn-Teller, symmetry breaking and core-hole localization. It is shown that while density functional theory gives very good transition energies in the symmetry-broken case, it gives a poor representation in the symmetry-restricted case, and an incomplete account of the Hartree-Fock localization energy.

  • 31. Niskanen, J.
    et al.
    Carravetta, V.
    Vahtras, O.
    Agren, H.
    Aksela, H.
    Andersson, E.
    Hedin, L.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Eland, J. H. D.
    Karlsson, L.
    Rubensson, J. -E
    Feifel, R.
    Experimental and theoretical study of core-valence double photoionization of OCS2010Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 82, nr 4, s. 043436-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    O 1s, C 1s, and S 2p core-valence double ionization electron spectra of the OCS molecule have been obtained experimentally by a time-of-flight photoelectron-photoelectron coincidence spectroscopy technique. In order to analyze and assign the spectral features observed, we present a protocol for computing core-valence ionization energies of such systems. The protocol is based on a restricted active space multiconfigurational self-consistent field (MCSCF) methodology with a freeze-relax procedure to guarantee a correct core-valence state root index without variational collapse. Corrections for extended dynamical correlation and core-core correlation, respectively, are made by multiconfigurational perturbation theory and by uncontracted basis set Moller-Plesset theory. Envisioning applications to larger molecules, a spin-restricted open-shell density functional method is also applied for the lowest core-valence energies. Furthermore, cross sections through a scheme for computing multiatom Auger transitions generating core-valence holes are presented. We find that the procedure outlined is capable of deriving the energy onset of core-valence ionization within a fraction of an eV and that assignments can be made of the most salient spectral features.

  • 32. Plogmaker, Stefan
    et al.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Eland, John H. D.
    Baker, Neville
    Johansson, Erik M. J.
    Rensmo, Håkan
    Feifel, Raimund
    Siegbahn, Hans
    Versatile high-repetition-rate phase-locked chopper system for fast timing experiments in the vacuum ultraviolet and x-ray spectral region2012Ingår i: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 83, nr 1, s. 013115-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A novel light chopper system for fast timing experiments in the vacuum-ultraviolet (VUV) and x-ray spectral region has been developed. It can be phase-locked and synchronized with a synchrotron radiation storage ring, accommodating repetition rates in the range of similar to 8 to similar to 120 kHz by choosing different sets of apertures and subharmonics of the ring frequency (MHz range). Also the opening time of the system can be varied from some nanoseconds to several microseconds to meet the needs of a broad range of applications. Adjusting these parameters, the device can be used either for the generation of single light pulses or pulse packages from a microwave driven, continuous He gas discharge lamp or from storage rings which are otherwise often considered as quasi-continuous light sources. This chopper can be utilized for many different kinds of experiments enabling, for example, unambiguous time-of-flight (TOF) multi-electron coincidence studies of atoms and molecules excited by a single light pulse as well as time-resolved visible laser pump x-ray probe electron spectroscopy of condensed matter in the valence and core level region.

  • 33. Sheinerman, S.
    et al.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Eland, J. H. D.
    Hedin, L.
    Andersson, E.
    Rubensson, J-E
    Karlsson, L.
    Feifel, R.
    Influence of double Auger decay on low-energy 3d photoelectrons of krypton2012Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 86, nr 2, s. 022515-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Effects of postcollision interaction (PCI) observable in low-energy 3d photoelectron spectra of Kr, which are associated with double Auger decay of the created inner-shell vacancy, are investigated by a combined experimental and theoretical approach. Measurements are based on an efficient multielectron coincidence method. Calculations have been carried out in the framework of a semiclassical approach. Our investigation reveals strong PCI distortion of the photoelectron line shapes, which depends on the kinematics of the process and the characteristics of the double Auger decay.

  • 34. Zagorodskikh, S.
    et al.
    Vapa, M.
    Vahtras, O.
    Zhaunerchyk, V.
    Mucke, M.
    Eland, J. H. D.
    Squibb, R. J.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Jänkälä, K.
    Ågren, H.
    Feifel, R.
    An experimental and theoretical study of core-valence double ionisation of acetaldehyde (ethanal)2016Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, nr 4, s. 2535-2547Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Core-valence double ionisation spectra of acetaldehyde (ethanal) are presented at photon energies above the carbon and oxygen 1s ionisation edges, measured by a versatile multi-electron coincidence spectroscopy technique. We use this molecule as a testbed for analyzing core-valence spectra by means of quantum chemical calculations of transition energies. These theoretical approaches range from two simple models, one based on orbital energies corrected by core valence interaction and one based on the equivalent core approximation, to a systematic series of quantum chemical electronic structure methods of increasing sophistication. The two simple models are found to provide a fast orbital interpretation of the spectra, in particular in the low energy parts, while the coverage of the full spectrum is best fulfilled by correlated models. CASPT2 is the most sophisticated model applied, but considering precision as well as computational costs, the single and double excitation configuration interaction model seems to provide the best option to analyze core-valence double hole spectra.

  • 35. Zagorodskikh, S.
    et al.
    Zhaunerchyk, V.
    Mucke, M.
    Eland, J. H. D.
    Squibb, R. J.
    Karlsson, L.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Feifel, R.
    Single-photon double and triple ionization of acetaldehyde (ethanal) studied by multi-electron coincidence spectroscopy2015Ingår i: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 463, s. 159-168Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Single-photon multiple ionization processes of acetaldehyde (ethanal) have been experimentally investigated by utilizing a multi-particle coincidence technique based on the time-of-flight magnetic bottle principle, in combination with either a synchrotron radiation source or a pulsed helium discharge lamp. The processes investigated include double and triple ionization in the valence region as well as single and double Auger decay of core-ionized acetaldehyde. The latter are studied site-selectively for chemically different carbon core vacancies, scrutinizing early theoretical predictions specifically made for the case of acetaldehyde. Moreover, Auger processes in shake-up and core-valence ionized states are investigated. In the cases where the processes involve simultaneous emission of two electrons, the distributions of the energy sharing are presented, emphasizing either the knock-out or shake-off mechanism.

  • 36. Zagorodskikh, Sergey
    et al.
    Eland, John H. D.
    Zhaunerchyk, Vitali
    Mucke, Melanie
    Squibb, Richard J.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Feifel, Raimund
    Mechanisms of site-specific photochemistry following core-shell ionization of chemically inequivalent carbon atoms in acetaldehyde (ethanal)2016Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 145, nr 12, artikel-id 124302Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Site-specific fragmentation upon 1s photoionisation of acetaldehyde has been studied using synchrotron radiation and a multi-electron-ion coincidence technique based on a magnetic bottle. Experimental evidence is presented that bond rupture occurs with highest probability in the vicinity of the initial charge localisation and possible mechanisms are discussed. We find that a significant contribution to site-specific photochemistry is made by different fragmentation patterns of individual quantum states populated at identical ionisation energies.

  • 37. Zhaunerchyk, V.
    et al.
    Kamińska, Magdalena
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. 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
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Meulen, Peter v. d.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Thomas, Richard D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Larsson, Mats
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    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 radiation2015Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 48, nr 24, artikel-id 244003Artikel i tidskrift (Refereegranskat)
    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).

  • 38. Zhaunerchyk, V.
    et al.
    Mucke, M.
    Salén, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    van der Meulen, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Kaminska, M.
    Squibb, R. J.
    Frasinski, L. J.
    Siano, M.
    Eland, J. H. D.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Thomas, Richard D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Larsson, Mats
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    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.
    Using covariance mapping to investigate the dynamics of multi-photon ionization processes of Ne atoms exposed to X-FEL pulses2013Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 46, nr 16, s. 164034-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report on a detailed investigation into the electron emission processes of Ne atoms exposed to intense femtosecond x-ray pulses, provided by the Linac Coherent Light Source Free Electron Laser (FEL) at Stanford. The covariance mapping technique is applied to analyse the data, and the capability of this approach to disentangle both linear and nonlinear correlation features which may be hidden on coincidence maps of the same data set is demonstrated. Different correction techniques which enable improvements on the quality of the spectral features extracted from the covariance maps are explored. Finally, a method for deriving characteristics of the x-ray FEL pulses based on covariance mapping in combination with model simulations is presented.

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