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  • 1.
    Ali, S.
    et al.
    Univ Stockholm, Dept Phys, S-10691 Stockholm, Sweden.
    Orban, I.
    Univ Stockholm, Dept Phys, S-10691 Stockholm, Sweden.
    Mahmood, S.
    Univ Stockholm, Dept Phys, S-10691 Stockholm, Sweden.
    Altun, Z.
    Marmara Univ, Dept Phys, TR-81040 Istanbul, Turkey.
    Glans, Peter
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för tillämpad naturvetenskap och design.
    Schuch, R.
    Univ Stockholm, Dept Phys, S-10691 Stockholm, Sweden.
    ELECTRON-ION RECOMBINATION RATE COEFFICIENTS FOR C II FORMING C I2012Inngår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 753, nr 2, s. Art. no. 132-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have determined absolute dielectronic recombination rate coefficients for C II, using the CRYRING heavy-ions storage ring. The resonances due to 2s-2p (Delta n= 0) core excitations are detected in the center-of-mass energy range of 0-15 eV. The experimental results are compared with intermediate coupling AUTOSTRUCTURE calculations. Plasma rate coefficients are obtained from the DR spectrum by convoluting it with a Maxwell-Boltzmann energy distribution for temperatures in the range of 10(3)-10(6) K. The derived temperature-dependent plasma recombination rate coefficients are presented graphically and parameterized by using a fit formula for convenient use in plasma modeling codes. The experimental rate coefficients are also compared with the theoretical data available in literature. In the temperature range of 10(3)-2 x 10(4) K, our experimental results show that previous calculations severely underestimate the plasma rate coefficients and also our AUTOSTRUCTURE calculation does not reproduce the experimental plasma rate coefficients well. Above 2x10(4) K, the agreement between the experimental and theoretical rate coefficients is much better, and the deviations are smaller than the estimated uncertainties.

  • 2.
    Butorin, S.M
    et al.
    Mittuniversitetet.
    Guo, J.H.
    Wassdahl, N
    Bray, G
    Glans, Peter
    Wiell, T
    Duda, L.C.
    Nordgren, J
    Lundström, T
    Klauda, M
    Markl, J
    Fink, C
    Saemannischenko, G
    Tunable excitation x-ray-fluorescence spectroscopy in phase-analysis of high-Tc superconductors1994Inngår i: Journal of physics-condensed matter, ISSN 0953-8984, Vol. 6, nr 43, s. 9267-9274Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    O Kalpha x-ray fluorescence of YBa2Cu3O7-delta and Sr0.85Nd0.15CuO2 samples containing CO3(2-) impurities, as well as pure BaCO3, have been studied using tunable monochromatic synchrotron radiation excitation. When the excitation energy is set to the most intense features in the O 1s absorption edge of cuprates and to bound states above this edge the O Kalpha spectra recorded are very similar to those of pure BaCO3 even if the admixture of CO3(2-) is small. The observed changes in the O Kalpha profiles of multi-phase YBa2Cu3O7-delta and Sr0.85Nd0.15CuO2 samples are discussed in terms of different x-ray absorption cross sections for O in the main phase and in the CO3(2-) fraction.

  • 3. Böhm, S
    et al.
    Müller, A
    Schippers, S
    Shi, W
    Fogle, M
    Glans, Peter
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Schuch, R
    Danared, H
    Experimental NV and NeVIII low-temperature dielectronic recombination rate coefficients2005Inngår i: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 437, nr 3, s. 1151-1157Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The dielectronic recombination rate coefficients of Nv and Ne viii ions have been measured at a heavy-ion storage ring. The investigated energy ranges covered all dielectronic recombination resonances attached to 2s -> 2p (delta_n = 0) core excitations. The rate coefficients in a plasma are derived and parameterized by using a convenient fit formula. The experimentally derived rate coefficients are compared with theoretical data by Colgan et al. (2004, A&A, 417, 1183) and Nahar & Pradhan (1997, ApJ, 111, 339) as well as with the recommended rate coefficients by Mazzotta et al. (1998, A&A, 133, 403). The data of Colgan et al. and Nahar & Pradhan reproduce the experiment very well over the temperature ranges where Nv and Ne viii are expected to exist in photoionized as well as in collisionally ionized plasmas. In contrast the recommendation of Mazzotta et al. agrees with the experimental rate coefficient only in the collisionally ionized temperature range. At lower temperatures it deviates from the measured rate coefficient by orders of magnitude. In addition the influence of external electric fields with field strengths up to 1300 V/cm on the dielectronic recombination rate coefficient has been investigated.

  • 4. Böhm, S
    et al.
    Schippers, S
    Shi, W
    Muller, A
    Djuric, N
    Dunn, G.H.
    Zong, W
    Jelencovic, B
    Eklöw, N
    Glans, Peter
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Schuch, R
    Danared, H
    Badnell, N.R.
    Influence of electromagnetic fields on the dielectronic recombination of Ne7+ and O5+ ions2001Inngår i: Physica Scripta. Topical Issues, ISSN 0281-1847, Vol. T92, s. 395-397Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Within a series of measurements of the dielectronic recombination (DR) of lithium-like ions we have determined the enhancement of the recombination rate in the presence of crossed electric and magnetic fields for Ne7+ and O5+ ions. In both cases the electron energy range covers a DR resonances attached to 2s --> 2p(1/2) and 2s --> 2p(3/2) Delta_n = 0 core excitations. For increasing field the enhancement factor first increases linearly with the electric field and then saturates. In order to investigate the field effect on high-n Rydberg states the ion energy in the O5+ experiment was changed from 9.4 MeV/u to 5 MeV/u and 3.26 MeV/u. With the variation of the ion energy the field ionization of Rydberg states in the analyzing magnet is influenced. This enabled us to study the field enhancement for a narrow bandwidth of n-states.

  • 5. Böhm, S
    et al.
    Schippers, S
    Shi, W
    Muller, A
    Djuric, N
    Dunn, G.H.
    Zong, W
    Jelenkovic, B
    Danared, H
    Eklöw, N
    Glans, Peter
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Schuch, R
    Badnell, N.R.
    Enhancement of dielectronic recombination by external electromagnetic fields2003Inngår i: Hyperfine Interactions, ISSN 0304-3843, Vol. 146-147, nr 1-4, s. 23-27Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The enhancement of the dielectronic recombination rate of lithiumlike Ne7+ and O5+ ions by external electromagnetic fields has been measured at the storage ring CRYRING. The energy range covered all 1s(2)2pnl dielectronic recombination resonances attached to the 2s --> 2p core excitation. Electric fields up to 1436 V/cm were applied in the Ne7+ experiment and the saturation of the enhancement with increasing electric field could clearly be seen. In the O5+ experiment the enhancement was studied as a function of the Rydberg quantum number n.

  • 6. Böhm, S
    et al.
    Schippers, S
    Shi, W
    Muller, A
    Djuric, N
    Dunn, G.H.
    Zong, W
    Jelenkovich, B
    Danared, H
    Eklöw, N
    Glans, Peter
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Schuch, R
    Influence of electromagnetic fields on the dielectronic recombination of Ne7+ ions2001Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, Vol. 64, nr 3, s. 032707/1-032707/7Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The influence of crossed electric and magnetic fields on dielectronic recombination of Ne7+ ions has been measured at the Stockholm heavy-ion storage ring CRYRING. The electron energy range covered all dielectronic recombination resonances attached to 2s-2p1/2 and 2s-2p3/2 core excitations. Two sets of measurements at magnetic fields of 180 mT and 30 mT have been performed. For the measurement at 180 mT we applied 25 different electric fields between 0 and 1400 V/cm. The resonance strength for dielectronic recombination via high Rydberg states initially increases linearly with electric field and later levels out. At a magnetic field of 30 mT we applied 15 different electric fields ranging from 0 to 140 V/cm. Compared to the measurement at 180 mT the initial slope of the rate enhancement was larger by almost a factor of 2. The fraction of resonant strength not measured due to field ionization is estimated by a model calculation of dielectronic recombination cross sections.

  • 7.
    Cesar, A
    et al.
    Mittuniversitetet.
    Gel'mukhanov, F.Kh
    Yi, L
    Ågren, H
    Skytt, P
    Glans, Peter
    Guo, J
    Gunnelin, K
    Nordgren, J
    Resonant x-ray scattering beyond the Born-Oppenheimer approximation: Symmetry breaking in the oxygen resonant x-ray emission spectrum of carbon dioxide1997Inngår i: Journal of Chemical Physics, ISSN 0021-9606, Vol. 106, nr 9, s. 3439-3456Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Although resonant x-ray scattering of molecules fulfills strict electronic symmetry selection rules, as now firmly proven by. spectra of diatomic molecules, the accumulated body of data for polyatomic molecules indicates that an apparent breaking of these rules represents the common situation rather than the exception. The CO2 molecule provides a good example of symmetry breaking, with the. oxygen x-ray emission spectra showing strong intensity for transitions that are forbidden by the parity selection rule. We present time-independent and time-dependent theories for frequency-dependent resonant x-ray scattering beyond, the Born-Oppenheimer approximation in order to explore under what circumstances one can anticipate symmetry breaking in the spectra of polyatomic molecules. The theory starts out from the Kramers-Heisenberg dispersion relation and is generalized for vibrational degrees of freedom and for nonadiabatic coupling of the electronic (vibronic) states, including the frequency dependency of, the scattering cross section. Different Limiting cases and few-level models are considered. The symmetry breaking is proven to be the result of pseudo-Jahn-Teller-Like vibronic coupling between near-degenerate core-excited states. Thus vibromic interaction over the antisymmetric vibrational mode between the ''bright'' 1 sigma(g)(-1)2 pi(u)(-1) and ''dark'' 1 sigma(u)(-1)2 pi(u)(-1) intermediate states of CO2 allows transitions otherwise forbidden. The measurements and theory demonstrate that the symmetry-selective character of the resonant x-ray emission is strongly frequency dependent. The strong intensity of ''dipole-forbidden'' transitions in the pi* oxygen K spectrum at resonance is reduced monotonically with the detuning of the excitation energy from resonance, and the spectra become ''symmetry purified.'' Simulations with full vibronic coupling predict this feature of the x-ray scattering experiment and a few-level model explains the energy dependence of the symmetry selection and the symmetry purification at large detuning energies in the limit of narrowband photon excitation.

  • 8. Derevianko, A
    et al.
    Hemmers, O
    Oblad, S
    Glans, Peter
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Wang, H
    Whitfield, S.B.
    Wehlitz, R
    Sellin, I.A.
    Johnson, W.R.
    Lindle, D.W.
    Electric-octupole and pure-electric-quadrupole effects in soft-X-ray photoemission2000Inngår i: Physical Review Letters, ISSN 0031-9007, Vol. 84, nr 10, s. 2116-2119Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Second-order [O(k(2)), k = omega/c] nondipole effects in soft-x-ray photoemission are demonstrated via an experimental and a theoretical study of angular distributions of neon valence photoelectrons in the 100-1200 eV photon-energy range. A newly derived theoretical expression for nondipolar angular distributions characterizes the second-order effects using four new parameters with primary contributions from pure-quadrupole and octupole-dipole interference terms;Independent-particle calculations of these parameters account for a significant portion of the existing discrepancy between experiment and theory for Ne 2p first-order nondipole parameters.

  • 9.
    Dias, E.W.B
    et al.
    Mittuniversitetet.
    Chakraborty, H.S.
    Deshmukh, P.C.
    Manson, S.T.
    Hemmers, O
    Glans, Peter
    Hansen, D.L.
    Wang, H
    Whitfield, S.B.
    Lindle, D.W.
    Wehlitz, R
    Levin, J.C.
    Sellin, I.A
    Perera, R.C.C
    Breakdown of the independent particle approximation in high-energy photoionization1997Inngår i: Physical Review Letters, ISSN 0031-9007, Vol. 78, nr 24, s. 4553-4556Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The independent particle approximation is shown to break down for the photoionization of both inner and outer nl (l > 0) electrons of all atoms, at high enough energy, owing to interchannel interactions with the nearby ns photoionization channels. The effect is illustrated for Ne 2p in the 1 keV photon energy range through a comparison of theory and experiment. The implications for x-ray photoelectron spectroscopy of molecules and condensed matter are discussed.

  • 10. Eklöw, N
    et al.
    Glans, Peter
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Zong, W
    Schuch, R
    Danared, H
    Magnetic-field dependence in electron-deuteron recombination at very low relative energy2000Inngår i: Hyperfine Interactions, ISSN 0304-3843, E-ISSN 1572-9540, Vol. 127, nr 1-4, s. 251-255Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The rate coefficient for recombination of D+ with low-energy electrons has been measured at different magnetic fields in the interaction region of the electron cooler at CRYRING. It is found that the measured recombination rate coefficient is influenced by the magnetic field.

  • 11. Fogle, M
    et al.
    Badnell, N.R.
    Glans, Peter
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Loch, S.D.
    Madzunkov, S
    Abdel-Naby, Sh.A.
    Pindzola, M.S.
    Schuch, R
    Electron-ion recombination of Be-like C, N, and O2005Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 442, nr 2, s. 757-766Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The absolute total recombination reaction rate coefficients for Be-like C, N, and O have been measured using the CRYRING storage ring and compared with the results from distorted-wave theory. For the theory results, it is found that shifts to NIST energy values for the core excited energies of the recombining system are not sufficient to accurately match all of the resonance positions and heights at lower energies. These theory results represent the quality of most archived theory DR data. The accurate calculation of these low energy resonances still presents a significant challenge to theory. In addition, trielectronic recombination resonances, associated with the formation of triply excited states during recombination, have been observed in the total recombination reaction rate coefficient spectra of N3+ and O4+. Finally, we construct a dielectronic recombination Maxwellian rate coefficient from the experimental results for low n resonances, and from the theoretical results for high n resonances. In the case of O4+, the trielectronic recombination resonances have a strong influence on the low temperature Maxwellian rate coefficient. Our best hybrid Maxwellian rate coefficient is compared with archived distorted-wave theory data, and is found to be in reasonable agreement, even at the low temperatures.

  • 12.
    Glans, Peter
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Fogle, M.
    Stockholm University.
    Madzunkov, S.
    Stockholm University.
    Tokman, M.
    Stockholm University.
    Nikolic, D.
    Stockholm University.
    Mohamed, T.
    Stockholm University.
    Eklöw, N.
    Stockholm University.
    Badnell, N.R.
    University of Strathclyde, United Kingdom.
    Lindroth, E.
    Stockholm University.
    Schuch, R.
    Stockholm University.
    Dielectronic recombination used as a tool for spectroscopic studies of highly charged ions2004Inngår i: Physica scripta. T, ISSN 0281-1847, Vol. T110, s. 212-215Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Systematic studies of electron-ion recombination for Li-like, Na-like, and Cu-like ions have been made during the last few years at the CRYRING facility. The main purpose has been to measure recombination spectra with such high resolution and accuracy that stringent tests of advanced atomic calculations of doubly excited states can be made. From the comparison with theory it is possible to obtain energy positions, as well as radiative and nonradiative decay rates for the doubly excited states. In addition, for heavy, highly charged ions it is possible to deduce radiative corrections for energy splittings with very high accuracy.

  • 13.
    Glans, Peter
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Gunnelin, K
    Skytt, P
    Guo, J.H.
    Wassdahl, N
    Nordgren, J
    Ågren, H
    Gelmukhanov, F.K.
    Warwick, T
    Rotenberg, E
    Resonant x-ray emission spectroscopy of molecular oxygen1996Inngår i: Physical Review Letters, ISSN 0031-9007, Vol. 76, nr 14, s. 2448-2451Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Resonant soft x-ray emission spectroscopy has been applied to study the issue of symmetry breaking upon core-hole excitation in molecular oxygen. The results provide direct evidence that the inversion symmetry is not broken in the core-excited states. Furthermore, the experiments themselves demonstrate a new experimental technique of broad applicability for studies of electronic structure and excitation dynamics in free atoms and molecules.

  • 14.
    Glans, Peter
    et al.
    Mittuniversitetet.
    LaVilla, R.E.
    Luo, Y
    Ågren, H
    Nordgren, J
    X-ray emission spectroscopy measurements of fluorine substituted methanes1994Inngår i: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, Vol. 27, nr 15, s. 3399-3414Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present the carbon and fluorine x-ray emission spectra of methane and the fluoromethanes (CH4-xFx, x = 0, 1, 2, 3 and 4), measured in high resolution. Relative x-ray emission intensities in dipole velocity and length gauges have been derived from the independent particle approximation using Hartree Fock ground state molecular orbitals. The results of the calculations are compared with the experimental spectra. In the experimental carbon (K-V) emission spectrum of CF4 We observe dipole-forbidden electronic transitions. We suggest that these transitions arise due to vibronic coupling, i.e. intensity is borrowed from the dipole-allowed transitions.

  • 15.
    Glans, Peter
    et al.
    Mittuniversitetet.
    LaVilla, R.E.
    Ohno, M
    Svensson, S
    Bray, G
    Wassdahl, N
    Nordgren, J
    Determination of the lifetime width of the argon L1-hole state1993Inngår i: Physical Review A (Atomic, Molecular, and Optical Physics), ISSN 1050-2947, Vol. 47, nr 2, s. 1539-1542Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The width of the argon 2s level was experimentally obtained from x-ray emission-spectroscopy (2.25+/-0.15 eV) and x-ray photoelectron-spectroscopy (XPS) (2.25+/-0.05 eV) measurements. A theoretical value of 1.85 eV was obtained by a Green's-function calculation. A high-energy satellite located 2.7+/-0.2 eV above the L1-M2,3 x-ray emission transition was confirmed and identified as the 2s(-1)3p-1-->3p-2 double-hole transition. The XPS measurement of the argon 2s ionization energy gave a value of 326.25(5) eV.

  • 16.
    Glans, Peter
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Lindroth, E
    Badnell, N.R.
    Eklöw, N
    Zong, W
    Justiniano, E
    Shuch, R
    Dielectronic recombination of N4+2001Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, Vol. 649, nr 4, s. 043609/1-043609/11Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The dielectronic recombination spectrum of N4+ has been measured with high resolution and accuracy. The 1s22p5l resonances in the energy range from 0 to 1.6 eV were studied in detail. The experimental spectrum is compared with the results from four different calculations. An almost perfect agreement between the experiment and a calculation which combines relativistic many-body perturbation theory and complex rotation is found. The calculation provides accurate spectroscopic data for all fifty 1s22p5l states. The literature value for the 1s22p5s 1P energy level is found to be off by more than 0.1 eV.

  • 17.
    Glans, Peter
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Lindroth, E
    Eklöw, N
    Zong, W
    Gwinner, G
    Saghiri, A.A.
    Pajek, M
    Danared, H
    Schuch, R
    Dielectronic recombination of Li-like fluorine ions1999Inngår i: Nuclear Instruments & Methods in Physics Research, Section B (Beam Interactions with Materials and Atoms), ISSN 0168-583X, Vol. 154, nr 1-4, s. 97-101Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Some recent new developments in dielectronic recombination (DR) measurements at heavy-ion storage rings are presented. A DR spectrum measured at CRYRING in Stockholm of F6+ is used to illustrate a few points regarding this kind of measurements. From the spectrum a transversal temperature of the adiabatically expanded electron beam of 3.0(5) meV is deduced, which is slightly higher than expected.

  • 18.
    Glans, Peter
    et al.
    Mittuniversitetet.
    Nordgren, J
    Ågren, H
    Cesar, A
    Experimental and theoretical investigation of the soft x-ray emission spectrum of molecular oxygen1993Inngår i: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, Vol. 26, nr 4, s. 663-673Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A high-resolution x-ray emission spectrum of molecular oxygen is presented. Comparisons with ab initio calculations are made regarding relative intensities, energies, and band profiles for the outer valence, 2PI(g), 4PI(u), 2PI(u), 4SIGMA(g)-, 2SIGMA(g)-, levels. The importance of lifetime-vibrational interference is discussed.

  • 19.
    Glans, Peter
    et al.
    Mittuniversitetet.
    Skytt, P
    Gunnelin, K
    Guo, J.H.
    Nordgren, J
    Selectively excited x-ray emission spectra of N21996Inngår i: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, Vol. 82, nr 3, s. 193-201Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Resonant and non-resonant X-ray emission spectra of N-2 are presented. The role of the parity selection rule in the case of homonuclear diatomic molecules is discussed thoroughly and illustrated by the X-ray emission spectra. We also discuss how the parity selection rule and the angular anisotropy of the resonant X-ray emission may affect intensities in a fluorescence yield measurement of N-2. Simulated vibrational band profiles calculated using the lifetime-vibrational interference formula are found to be in excellent agreement with the experimental emission bands.

  • 20.
    Gunnelin, K
    et al.
    Mittuniversitetet.
    Glans, Peter
    Rubensson, J.E.
    Såthe, C
    Nordgren, J
    Li, Y
    Gel'mukhanov, F
    Ågren, H
    Bond-length-dependent core hole localization observed in simple hydrocarbons1999Inngår i: Physical Review Letters, ISSN 0031-9007, Vol. 83, nr 7, s. 1315-1318Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Soft x-ray-emission spectroscopy is applied to measure the amount of dynamic symmetry breaking in core-excited acetylene, ethylene, and ethane. Large variations are observed between the molecules and are rationalized in terms of the different C-C bond lengths: Shorter bond lengths give smaller symmetry breaking. The results also indicate that asymmetric modes are important for all the systems studied, in contradiction to previous assumptions in literature.

  • 21.
    Gunnelin, K
    et al.
    Mittuniversitetet.
    Glans, Peter
    Skytt, P
    Guo, J.H.
    Nordgren, J
    Ågren, H
    Assigning x-ray absorption spectra by means of soft-x-ray emission spectroscopy1998Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, Vol. 57, nr 2, s. 864-872Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The possibility to symmetry assign x-ray absorption spectra using x-ray emission spectroscopy is demonstrated. The oxygen K spectra of CO2 are used to illustrate the possibility to assign core excitations through excitation-energy and angular dependence of resonantly excited x-ray emission spectra. The Rydberg-associated structures just below the ionization threshold in the O K x-ray absorption spectrum are assigned to be mainly due to excitations to orbitals of sigma(g) character. The results, which contradict some previous literature assignments, are supported by quantum-chemical calculations.

  • 22.
    Guo, J.H.
    et al.
    Mittuniversitetet.
    Glans, Peter
    Skytt, P
    Wassdahl, N
    Nordgren, J
    Luo, Y
    Ågren, H
    Ma, Y
    Warwick, T
    Heimann, P
    Rotenberg, E
    Denlinger, J.D.
    Resonant excitation x-ray-fluorescence from C-601995Inngår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 52, s. 10681-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    X-ray fluorescence of condensed C-60 has been recorded in high resolution using monochromatic synchrotron radiation excitation. Strong intensity modulation of constituent spectral features is observed with varying excitation energy up to 10 eV above threshold. The energy dependence is interpreted as due to resonant inelastic x-ray scattering, leading to symmetry selection rules governing the two-photon process in the fully symmetric molecule.

  • 23. Gwinner, G.
    et al.
    Hoffknecht, A.
    Bartsch, T.
    Beutelspacher, M.
    Eklöw, N.
    Glans, Peter
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Grieser, M.
    Krohn, S.
    Lindroth, E.
    Muller, A.
    Saghiri, A.A.
    Schippers, S.
    Schramm, U.
    Schwalm, D.
    Tokman, M.
    Wissler, G.
    Wolf, A.
    Influence of magnetic fields on electron-ion recombination at very low energies2000Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 84, nr 21, s. 4822-4825Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Radiative recombination (inverse photoionization) is believed to be well understood since the beginning of quantum mechanics. Still, modern experiments consistently reveal excess recombination rates at very low electron-ion center-of-mass energies. In a detailed study on recombination of F and C ions with magnetically guided electrons we explored the yet unexplained rate enhancement, its dependence on the magnetic field B, the electron density n(e), and the beam temperatures T-perpendicular to and T-parallel to. The excess scales as T-perpendicular to(-1/2) and, surprisingly, as T-parallel to(-1/2), increases strongly with B, and is insensitive to n(e). This puts strong constraints on explanations of the enhancement.

  • 24. Hemmers, O.
    et al.
    Blackburn, M.
    Goddard, T.
    Glans, Peter
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Wang, H.
    Whitfield, S.B.
    Wehlitz, R.
    Sellin, I.A.
    Lindle, D.W.
    Dipole and nondipole angular-distribution effects in valence photoemission from neon2002Inngår i: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, Vol. 123, nr 2-3, s. 257-264Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Nondipole angular-distribution parameters γ and δ for neon 2s and 2p photoelectrons have been measured and are compared to all available theoretical data. The agreement is very good throughout the 150-1200 eV photon-energy range studied. Furthermore, the neon 2p dipole angular-distribution parameter β and the 2s to 2p cross-section ratio have been measured throughout the same photon-energy range. The agreement between theoretical data and experiment is excellent.

  • 25.
    Hemmers, O
    et al.
    Mittuniversitetet.
    Fisher, P
    Glans, Peter
    Hansen, D.L.
    Wang, H
    Whitfield, S.B.
    Wehlitz, R
    Levin, J.C
    Sellin, I.A.
    Perera, R.C.C.
    Dias, E.W.B.
    Chakraborty, H.S.
    Deshmukh, P.C.
    Manson, S.T.
    Lindle, D.W.
    Beyond the dipole approximation: angular-distribution effects in valence photoemission1997Inngår i: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, Vol. 30, nr 21, s. L727-L733Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Angular distributions of valence photoelectrons showing effects due to highermultipole photon interactions have been measured for the first time. Neon 2s and 2p photoemission exhibits effects beyond the dipole approximation throughout the 250 to 1200 eV photon-energy range studied. The results suggest that any photoemission experiment, on any sample, can be affected at relatively low photon energies, pointing to a general need for caution in interpreting angle-resolved-photoemission measurements.

  • 26.
    Hemmers, O
    et al.
    Mittuniversitetet.
    Whitfield, S.B.
    Glans, Peter
    Wang, H
    Lindle, D.W.
    Wehlitz, R
    Sellin, I.A.
    High-resolution electron time-of-flight apparatus for the soft X-ray region1998Inngår i: Review of Scientific Instruments, ISSN 0034-6748, Vol. 69, nr 11, s. 3809-3817Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A gas-phase time-of-flight (TOF) apparatus, capable of supporting as many as six electron-TOF analyzers viewing the same interaction region, has been developed to measure energy- and angle-resolved electrons with kinetic energies up to 5 keV. Each analyzer includes a newly designed lens system that can retard electrons to about 2% of their initial kinetic energy without significant loss of transmission; the analyzers can thus achieve a resolving power (E/Delta_E) greater than 10(4) over a wide kinetic-energy range. Such high resolving power is comparable to the photon energy resolution of state-of-the-art synchrotron-radiation beamlines in the soft x-ray range, opening the TOF technique to numerous high-resolution applications. In addition, the angular placement of the analyzers, by design, permits detailed studies of nondipolar angular distribution effects in gas-phase photoemission.

  • 27.
    Hoffknecht, A
    et al.
    Mittuniversitetet.
    Bartsch, T
    Schippers, S
    Muller, A
    Eklöw, N
    Glans, Peter
    Beutelspacher, M
    Grieser, M
    Gwinner, G
    Saghiri, A.A.
    Wolf, A
    Recombination of F6+ with free electrons at very low energies1999Inngår i: Physica Scripta. Topical Issues, Vol. T80B, s. 298-300Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Radiative and dielectronic recombination of F6+ have been studied at the heavy ion storage ring TSR in Heidelberg. For a detailed investigation of rate enhancement effects at very low electron-ion center-of-mass energies experimental parameters such as the magnetic guiding field, the electron density and the adiabatic expansion factor of the electron beam have been varied systematically. Whereas measurements at different electron densities show no influence on the enhancement and while a variation of the expansion factor evokes the predicted behaviour, we see an increase of the enhancement with increasing axial magnetic field between 20 mT and 70 mT.

  • 28.
    Hutton, R
    et al.
    Mittuniversitetet.
    Huldt, S
    Nyström, B
    Heijkensköld, F
    Glans, Peter
    Larsson, M.O.
    Photon spectroscopy following electron-capture for the collision systems 10 keV/q Kr(q+) + He (q=7,8,9)1993Inngår i: Physica Scripta, ISSN 0031-8949, Vol. 48, nr 5, s. 569-572Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Spectral studies following electron capture in slow ion-atom collisions are reported for the collision systems Kr(q+) + He (q = 7, 8, 9) at 10 keV/q. The work introduces part of the spectroscopy program which is beginning at the University of Uppsala ECR ion source facility. In particular a search was made for the 3d(10)4p2P-3d(9)4S(2)2D transitions in Cu-like Kr. This multiplet was found to give transitions with wavelengths 198.56, 194.65 and 190.97 angstrom for the 3/2-5/2, 3/2-3/2 and 1/2-3/2 components respectively.

  • 29.
    LaVilla, R.E.
    et al.
    Mittuniversitetet.
    Ohno, M
    Glans, Peter
    Nordgren, J
    Additional features in the 3d-4p x-ray-emission spectrum of Xe1994Inngår i: Physical Review A - Atomic, Molecular, and Optical Physics, ISSN 1050-2947, Vol. 49, nr 3, s. 2185-2187Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The high-resolution 3d-4p x-ray-emission spectrum of Xe excited by electron impact was measured. In addition to the prominent peak due to 3d5/2-4p3/2 previously reported, the experimental high-resolution spectrum shows a weak peak, identified as 3d3/2-4P3/2, and satellites. The satellites are tentatively attributed to 3d-1X-1-4p-1X-1 (X = 4s, 4p, and 4d), where the initial doubly ionized states are created by the Auger (Coster-Kronig) decay of the 2p and/or 3p level. The experimental 3d-4p x-ray spectrum is compared with a theoretical spectrum calculated by the ab initio Green's-function method.

  • 30. Lindle, D.W.
    et al.
    Hemmers, O
    Glans, Peter
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Hansen, D.L
    Wang, H
    Whitfield, S.B.
    Wehlitz, R
    Levin, J.C.
    Sellin, I.A.
    Perera, R.C.C.
    The x-ray atomic and molecular spectroscopy program at the Advanced Light Source1997Inngår i: Indian Journal of Physics, Part B, ISSN 0252-9254, Vol. 71B, nr 3, s. 325-334Artikkel i tidsskrift (Fagfellevurdert)
  • 31. Lindroth, Eva
    et al.
    Danared, Håkan
    Glans, Peter
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Pešić, Z
    Tokman, M
    Vikor, György
    Schuch, Reinhold
    QED effects in Cu-like Pb recombination resonances near threshold2001Inngår i: Physical Review Letters, ISSN 0031-9007, Vol. 86, nr 22, s. 5027-5030Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In an electron-ion recombination study with Pb53+ dielectronic recombination resonances are found for as low as similar to 10(-3)-10(-4) eV relative energy. The resonances have been calculated by relativistic many-body perturbation theory and through comparison with experiment the Pb53+(4p(1/2)-4s(1/2)) energy splitting of similar to 118 eV is determined with an accuracy comparable to the position of the first few resonances, i.e., similar to 10(-3) eV. Such a precision provides a test of QED in a many-body environment at a level which can still not be reached in calculations.

  • 32. Loch, S.D.
    et al.
    Witthoeft, M
    Pindzola, M.S.
    Bray, I
    Fursa, D.V.
    Fogle, M.
    Schuch, R
    Glans, Peter
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Ballance, C.P.
    Griffin, D.C.
    Influence of long-lived metastable levels on the electron-impact single ionization of C2+2005Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 71, nr 1, s. 012716-1Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A joint theoretical and experimental investigation is made of the influence of long-lived metastable levels on the electron-impact single ionization of C2+. It is expected that our electron cyclotron resonance ion source produces a beam with 40% of the C2+ ions in the 1s(2)2s(2) S-1(0) ground level and 60% in the 1s(2)2s2p P-3(0,2) excited levels. The comparison of nonperturbative close-coupling calculations with previous single-pass crossed beams and with our multiple-pass storage-ring measurements for the electron-impact ionization of C2+ is consistent with the predicted large metastable fraction. Reasonable agreement is found between the present time-dependent close-coupling, R-matrix with pseudostates, and converged-close-coupling ionization cross-section calculations for the ground and first excited configurations and experimental measurement, assuming a 60% metastable fraction in the ion beam. Distorted-wave calculations are found to overestimate the ionization cross section from both the ground and metastable terms, compared with nonperturbative calculations, resulting in an overestimation of the resultant total cross section when compared with experiment. It is clear that collisional-radiative modeling of the evolution of atomic plasmas through the Be-like ionization stage will need to take into account the role of both ground and metastable levels.

  • 33. Ma, Y
    et al.
    Skytt, P
    Wassdahl, N
    Glans, Peter
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Mancini, D.C.
    Guo, J
    Nordgren, J
    Core excitons and vibronic coupling in diamond and graphite1993Inngår i: Physical Review Letters, ISSN 0031-9007, Vol. 71, nr 22, s. 3725-3728Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The C 1s exciton in diamond is studied by soft x-ray emission excited with high resolution monochromatic photons. A strong phonon sideband of 5 eV wide is observed in the exciton recombination spectrum. With the phonon contribution, the exciton binding energy is estimated to be 1.5 eV. The excited atom is suggested to undergo Jahn-Teller relaxation similar to that of the nitrogen impurities in diamond. A similar exciton is observed at the sigma*-band threshold in graphite. These results provide new insights to the understanding of the core exciton and the donor problem in diamond and other systems.

  • 34.
    Magnuson, M
    et al.
    Mittuniversitetet.
    Guo, J
    Såthe, C
    Rubensson, J.E.
    Nordgren, J
    Glans, Peter
    Yang, L
    Salek, P
    Ågren, H
    Competition between decay and dissociation of core-excited carbonyl sulfide studied by x-ray scattering1999Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, Vol. 59, nr 6, s. 4281-4287Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We show evidence of dissociation during resonant inelastic soft x-ray scattering Carbon and oxygen K-shell and sulfur L-shell resonant and nonresonant x-ray emission spectra were measured using monochromatic synchrotron radiation for excitation and ionization. After sulfur L-2,L-3-->pi*, sigma* excitation, atomic lines are observed in the emission spectra as a consequence of competition between de-excitation and dissociation. In contrast thr carbon and oxygen spectra show weaker line-shape variations and no atomic Lines. The spectra are compared to results from ab initio calculations. The discussion of the dissociation paths is based on calculated potential energy surfaces and atomic transition energies.

  • 35.
    Mahmood, S.
    et al.
    Stockholm Univ, Dept Phys, SE-10691 Stockholm, Sweden.
    Orban, I.
    Stockholm Univ, Dept Phys, SE-10691 Stockholm, Sweden.
    Ali, S.
    Stockholm Univ, Dept Phys, SE-10691 Stockholm, Sweden.
    Glans, Peter
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Bleda, E. A.
    Marmara Univ, Dept Phys, TR-81040 Istanbul, Turkey.
    Altun, Z.
    Marmara Univ, Dept Phys, TR-81040 Istanbul, Turkey.
    Schuch, R.
    Stockholm Univ, Dept Phys, SE-10691 Stockholm, Sweden.
    RECOMBINATION RATE COEFFICIENTS OF BORON-LIKE Ne2013Inngår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 771, nr 2, s. Art. no. 78-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Recombination of Ne5+ was measured in a merged-beam type experiment at the heavy-ion storage ring CRYRING. In the collision energy range 0-110 eV resonances due to 2s(2)2p -> 2s2p(2) (Delta n=0) and 2s(2)2p -> 2s(2)3l (Delta n=1), core excitations were observed. The experimentally derived rate coefficients agree well with the calculations obtained using AUTOSTRUCTURE. At low energies, recombination is dominated by resonances belonging to the spin-forbidden 2s2p(2)(P-4(J))nl series. The energy-dependent rate coefficients were convoluted with a Maxwell-Boltzmann electron energy distribution to obtain plasma recombination rate coefficients. The data from the literature deviate from the measured results at low temperature.

  • 36.
    Nordgren, J
    et al.
    Mittuniversitetet.
    Glans, Peter
    Gunnelin, K
    Guo, J
    Skytt, P
    Såthe, C
    Wassdahl, N
    Resonant soft X-ray fluorescence spectra of molecules1997Inngår i: Applied Physics A (Materials Science Processing), ISSN 0947-8396, Vol. 65, nr 2, s. 97-105Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A review is presented of some recent advancements in resonant soft X-ray fluorescence spectroscopy applied to molecules. The concept of inelastic scattering is discussed for molecules with an element of symmetry, which introduces degeneracy or near-degeneracy of core excited states. The potential of the symmetry selection rules associated with resonant X-ray fluorescence is illustrated in studies of electronic structure as well as molecular dynamics. The use of polarized photons for exciting X-ray emission is discussed, and examples are presented where anisotropy of X-ray emission provides more detailed information. A brief section discusses the experimental considerations relevant for the spectroscopic technique.

  • 37.
    Nordgren, J
    et al.
    Mittuniversitetet.
    Glans, Peter
    Wassdahl, N
    Progress in ultra-soft x-ray emission spectroscopy1991Inngår i: Physica Scripta. Topical Issues, ISSN 0281-1847, Vol. T34, s. 100-107Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A brief account is given of some recent developments in the use of ultra-soft X-ray emission spectroscopy for studies of electronic structure and excitation dynamics. In particular the novel technique of using monochromatized synchrotron radiation for the excitation of the emission is discussed and some key work presented. Also, photon emission studies in the ultra-soft X-ray range of charge transfer in slow collisions between highly charged ions and atoms are presented.

  • 38.
    Orban, I
    et al.
    Stockholm University.
    Glans, Peter
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Altun, Z.
    Marmara University, Istanbul, Turkey.
    Lindroth, E
    Stockholm University.
    Källberg, A.
    Stockholm University.
    Schuch, R.
    Stockholm University.
    Determination of the recombination rate coefficients for Na-like Si IV forming Mg-like Si III2006Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 459, nr 1, s. 291-296Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Aims. Absolute, total recombination rate coefficients for Si IV were determined using the CRYRING heavy-ion storage ring. Calculated rate coefficients were used to estimate recombination into states that could not be detected in the experiment because of field ionization. Total, as well as separate, radiative and dielectronic plasma recombination rate coefficients were determined. Methods. Stored ions were merged with an expanded electron beam in the electron cooler section of the storage ring. Recombined ions were separated from the stored ion beam in the first dipole magnet after the electron cooler and were detected with unity efficiency. The absolute radiative and dielectronic recombination rate coefficients were obtained over a center-of-mass energy range of 0-20 eV, covering Δ n = 0 core excitations up to the 3s → 3d series limit. The results of an intermediate coupling AUTOSTRUCTURE calculation were compared with the experiment. The theoretical results were also used to estimate the contribution to dielectronic recombination by high Rydberg states, which were not detected because of field ionization. The spectra were convoluted with Maxwell-Boltzmann energy distributions in the 103-10 6 K temperature range. Results. The resulting plasma recombination rate coefficients are presented and compared with theoretical results frequently used for plasma modeling. In the 103-104 K range, a significant underestimation of the calculated dielectronic recombination plasma rate coefficients was observed. Above 3 × 104 K, the agreement between our dielectronic recombination plasma rate coefficients and two of the previously published rate coefficients is better than 20%. Conclusions. The observed differences between the experimental and calculated recombination rate coefficients at low temperatures reflect the need for benchmarking experiments. Our experimentally-derived rate coefficients can guide the development of better theoretical models and lead to more accurately-calculated rate coefficients.

  • 39.
    Orban, I.
    et al.
    Stockholm University.
    Lindroth, E.
    Stockholm University.
    Glans, Peter
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Schuch, R.
    Stockholm University.
    Spectroscopic study of doubly excited states in Mg-like Si using dielectronic recombination2007Inngår i: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 40, nr 5, s. 1063-1080Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present calculated and experimentally derived electron-ion recombination rate coefficients for Na-like Si IV, recombining into Mg-like Si III, and provide accurate spectroscopic data for doubly excited states located above the ionization threshold of Si III. The experimental recombination rate coefficients were measured in a merged-beam-type experiment at the heavy-ion storage ring CRYRING at the Manne Siegbahn Laboratory in Stockholm. Changing the electron-ion relative energy from 0 to 20 eV we covered the energy region from the first to the third ionization threshold. We find that even for the low-charged Si2+ ion, a relativistic many-body perturbation theory calculation is necessary, to describe the recombination rate coefficients in the low-energy region, up to 1.5 eV, satisfactorily. Doubly excited states, forbidden to form in LS coupling, are responsible for the most prominent dielectronic recombination resonances at low energies and contribute with 40% to the strength. Several wide resonances give rise to a plateau-like formation in the recombination spectrum. A broader energy range, up to 6.7 eV, was covered with a non-relativistic many-body calculation. This range contains, in addition to 3pnl resonances, several resonances of the type 3dnl, with the LS-forbidden 3d(2) F-3 states giving rise to a strong, isolated peak at 2.976 eV. The NIST database lists eleven doubly excited states of Si III with energy positions deviating considerably from our determination. Since the listed lines are also not fully matching those with the largest fluorescence yields it must be concluded that they are misidentified.

  • 40.
    Orban, Istvan
    et al.
    Stockholm University, Department of Physics.
    Loch, Stuart D
    Auburn University, Department of Physics.
    Glans, Peter
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Böhm, Stefan
    Stockholm University, Department of Physics.
    Schuch, Reinhold
    Stockholm University, Department of Physics.
    Effects of spin-forbidden resonances on the recombination of Be-like Si and Be-like Ne2011Inngår i: Physics Scripta, ISSN 0031-8949, Vol. T144, s. Art. no. 014035-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Recombination through doubly excited states that can be formed only through spin-flip of the excited electrons can give very strong contributions to the recombination rate of Be-like ions. We demonstrate this, in this paper, with the electron-ion recombination spectra of Be-like Ne(6+) and Be-like Si(10+), recently measured at the CRYRING storage ring. These resonances have significant effects on the plasma rate coefficients. We show that neglect or imprecise calculation of these resonances is responsible for large spreads observed between various theoretical results from the literature.

  • 41.
    Schuch, R
    et al.
    Stockholm University.
    Fogle, M
    National Institute for Fusion Science, Toki, Gifu, Japan.
    Glans, Peter
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Lindroth, E
    Stockholm University.
    Madzunkov, S
    National Institute for Fusion Science, Toki, Gifu, Japan.
    Mohamed, T
    National Institute for Fusion Science, Toki, Gifu, Japan.
    Nikolic, D
    National Institute for Fusion Science, Toki, Gifu, Japan.
    High resolution studies of electron-ion recombination2003Inngår i: Radiation Physics and Chemistry, ISSN 0969-806X, Vol. 68, nr 1-2, s. 51-56Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The formation of atoms by recombination of free electrons with ions is a fundamental process and plays a central role in astro-physical and fusion plasmas. It can be seen as time-inverse photo-ionization, auto-ionization, or electron-impact ionization. Here, we show how these processes can be measured with cooler-storage rings, such as CRYRING at MSL, with very high accuracy. The status of theoretical modeling is briefly reviewed and anomalies are uncovered. We discuss some examples of recombination for ions where strong dielectronic recombination resonances occur. With cooler-storage rings, these resonances can today be measured with meV accuracy, and from the spectra of the dielectronic resonances, very accurate values for energy splittings and resonance strengths are derived. These allow crucial tests of relativistic, correlation, and QED effects in these systems.

  • 42.
    Schuch, R
    et al.
    Mittuniversitetet.
    Zong, W
    Spies, W
    Glans, Peter
    Danared, H
    A first study of dielectronic recombination with the super-expanded electron beam in CRYRING1998Inngår i: Hyperfine Interactions, ISSN 0304-3843, Vol. 115, nr 1-4, s. 123-127Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A first temperature measurement of the expanded electron beam from a super-conducting magnet in the cooler of CRYRING is reported. It is based on detection of a dielectronic recombination resonance in C2+. For this measurement C3+ was stored in the ring at 3 MeV/amu energy. A fit to the resonance with free transverse and longitudinal temperatures gave 3.9 x 10(-3) eV and 4.5 x 10(-5) eV,respectively. The result is also compatible with the values of 10(-3) eV for the transverse and 6.7 x 10(-5) eV for the longitudinal component, in good agreement with expected values.

  • 43.
    Skytt, P
    et al.
    Mittuniversitetet.
    Glans, Peter
    Gunnelin, K
    Guo, J.H.
    Nordgren, J
    Lifetime-vibrational interference effects in the resonantly excited x-ray-emission spectra of CO1997Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, Vol. 55, nr 1, s. 146-154Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A systematic study of vibrational band profiles in resonantly excited x-ray-emission spectra of free molecules is made. Carbon and oxygen K-emission spectra of CO following core excitations, using narrow-bandpass synchrotron radiation, to the 2 pi orbital an presented. Because of the short lifetime of the core-excited states, interference effects between close-lying coherently excited vibrational levels may occur. The importance of lifetime-vibrational interference in the carbon and oxygen x-ray-emission spectra is investigated by comparing the experimental band profiles with simulated profiles. It is shown that to properly describe the band profiles in the oxygen emission spectra it is necessary to include the interference contributions, while in the carbon spectra the interference contributions are important only when the excitation energy is tuned towards higher vibrational levels. For example, when the excitation energy is tuned to the upsilon=2 vibrational level significant interference effects are observed. It is also demonstrated how emission spectra recorded with a detuning of the excitation energy from the resonance can be used to check the shape of the photon distribution of the synchrotron radiation.

  • 44.
    Skytt, P
    et al.
    Mittuniversitetet.
    Glans, Peter
    Gunnelin, K
    Guo, J.H.
    Nordgren, J
    Luo, Y
    Ågren, H
    Role of screening and angular distributions in resonant x-ray emission of CO1997Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, Vol. 55, nr 1, s. 134-145Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Resonantly excited carbon and oxygen x-ray-emission spectra of gaseous carbon monoxide are presented. Emission spectra obtained with selective excitation to the pi* valence orbital and to various Rydberg levels are compared to satellite-free nonresonant spectra. Screening effects caused by the excited electron, creating energy shifts and intensity variations in the resonant spectra compared to the nonresonant spectra, are observed, as well as an angular dependence of the resonantly excited spectra. The experimental spectra are compared to simulated spectra where the vibronic part is computed by means of a lifetime-vibrational interference formalism. The electronic intensities are analyzed by a separate-state, self-consistent-held method and a formalism for resonant inelastic x-ray scattering, focusing On screening and angular dependence.

  • 45.
    Skytt, P
    et al.
    Mittuniversitetet.
    Glans, Peter
    Guo, J.H.
    Gunnelin, K
    Såthe, C
    Nordgren, J
    Gelmukhanov, F.K.
    Cesar, A
    Ågren, H
    Quenching of symmetry breaking in resonant inelastic X-ray scattering by detuned excitation1996Inngår i: Physical Review Letters, ISSN 0031-9007, Vol. 77, nr 25, s. 5035-5038Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Observations made in oxygen K emission of CO2 show that the symmetry selective character of resonant x-ray emission is excitation energy dependent. Electronically dipole forbidden O K emission lines are observed for excitation at the O 1s --> pi* resonance, and they are gradually reduced upon detuning the excitation energy below threshold. The occurrence of forbidden transitions is explained in terms of dynamical symmetry breaking due to vibronic coupling, and the observation of quenching of the symmetry breaking upon detuning as due to an effective quenching of this vibronic coupling. Scattering theory applied to a few-level system is shown to account for the energy dependence of the symmetry selection in the limit of narrow bandpass photon excitation.

  • 46.
    Skytt, P
    et al.
    Department ofPhysics, Uppsala University, Box 530, S-751 21 Uppsala, Sweden.
    Glans, Peter
    Department ofPhysics, Uppsala University, Box 530, S-751 21 Uppsala, Sweden.
    Mancini, D.C.
    Department ofPhysics, Uppsala University, Box 530, S-751 21 Uppsala, Sweden.
    Guo, J.H
    Department ofPhysics, Uppsala University, Box 530, S-751 21 Uppsala, Sweden.
    Wassdahl, N
    Department ofPhysics, Uppsala University, Box 530, S-751 21 Uppsala, Sweden.
    Nordgren, J
    Department ofPhysics, Uppsala University, Box 530, S-751 21 Uppsala, Sweden.
    Ma, Y
    Physics Department, University of Washington, Seattle, Washington 98195 and Molecular Science Research Centre, Pacijic Northwest Laboratories, Richland, Washington 99352.
    Angle-resolved soft-x-ray fluorescence and absorption study of graphite: Physical Review B (Condensed Matter)1994Inngår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 50, nr 15Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The x-ray fluorescence and absorption of highly oriented pyrolytic graphite have been measured using monochromatic synchrotron radiation. The spectra can be separated into contributions from pi- and sigma-band components by measuring at different angles of incidence and at different emission angles. The shape of the x-ray fluorescence spectra varies dramatically with excitation energy near the C K edge. This dependence on excitation energy can be interpreted within a resonant-inelastic-scattering formalism. The results are compared with previously published band-structure calculations and photoemission results, and demonstrate the potential for using x-ray fluorescence to obtain symmetry-resolved band information.

  • 47.
    Spies, W
    et al.
    Mittuniversitetet.
    Glans, Peter
    Zong, W
    Gao, H
    Andler, G
    Justiniano, E
    Saito, M
    Schuch, R
    Recombination experiments at CRYRING1998Inngår i: Hyperfine Interactions, ISSN 0304-3843, Vol. 114, nr 1-4, s. 237-243Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Recent advances in studies of electron-ion recombination processes at low relative energies with the electron cooler of the heavy-ion storage ring CRYRING are shown. Through the use of an adiabatically expanded electron beam, collisions down to 10(-4) eV relative energies were measured with highly charged ions stored in the ring at around 15 MeV/amu energies. Examples of recombination measurements for bare ions of D+, He2+, N7+, Ne10+ and Si14+ are presented. Further on, results of an experiment measuring laser-induced recombination (LIR) into n = 3 states of deuterium with polarized laser light are shown.

  • 48.
    Stolte, W.C.
    et al.
    Mittuniversitetet.
    Lu, Y
    Samson, J.A.R.
    Hemmers, O
    Hansen, D.L.
    Whitfield, S.B
    Wang, H
    Glans, Peter
    Lindle, D.W.
    The K-shell Auger decay of atomic oxygen1997Inngår i: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, Vol. 30, nr 20, s. 4489-4497Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Relative photoionization cross sections for O+ and O2+ produced by the Auger decay of a 1s hole in atomic oxygen were measured by using synchrotron radiation between 525 and 553 eV. Energies and quantum defects of the members of the two Rydberg series converging to [1s]2s22p4(4P) and [1s]2s22p4(2P) ionization thresholds were determined. In addition, the 2P and 4P ionization thresholds were calculated from the two Rydberg series. The 182 meV resolution of the monochromator allowed a detailed study over both thresholds revealing evidence for post-collision interaction and allowing a comparison of the ionization continuum above both 2P and 4P thresholds with that of the ionization continuum above the Ar L2 and L3 edges. This comparison indicates that the lifetimes of the Ar(2p) and O(1s) hole states are approximately the same.

  • 49. Tokman, M
    et al.
    Eklöw, N
    Glans, Peter
    Lindroth, E
    Schuch, R
    Gwinner, G
    Schwalm, D
    Wolf, A
    Hoffknecht, A
    Muller, A
    Schippers, S
    Dielectronic recombination resonances in F6+2002Inngår i: Physical Review A - Atomic, Molecular, and Optical Physics, ISSN 1050-2947, Vol. 66, nr 1, s. 012703/1-012703/13Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Electron-ion recombination spectra of the Li-like ion F6+ in the energy range 0.0-0.6 eV from two different ion storage rings are presented, showing excellent agreement. The experimental results are compared with a calculated spectrum, obtained by combination of relativistic many-body methods and complex rotation, and the agreement is found to be very good. The recombination spectrum in the studied energy region is determined by the 2p6l dielectronic recombination resonances. The lowest-energy resonances are found around 10 meV, and include one broad resonance overlapping the threshold. The recombination rate coefficients are, even in this region, very well accounted for by the calculation. It is further shown that the nonrelativistically allowed resonances contribute to less than 60% of the integrated rate coefficients in the specified energy range.

  • 50. Tokman, M
    et al.
    Glans, Peter
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Lindroth, E
    Pesic, Z
    Schuch, R
    Vikor, G
    Accurate calculations on dielectronic recombination resonances in Cu-like Pb2001Inngår i: Hyperfine Interactions, ISSN 0304-3843, Vol. 132, nr 1-4, s. 383-389Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Dielectronic recombination of Pb53+ has been studied and a resonance is detected only similar to 0.1 meV above the ground state. The possibility to determine the 4p(1/2) - 4s(1/2) energy splitting with a similar accuracy from the determination of the resonance position is discussed. Such a precision can only be achieved by calculations which treat QED in a many-body environment at levels which can still not be reached. A fully relativistic many-body calculation of the splitting is described and the uncertainties are discussed.

12 1 - 50 of 53
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