| 1. |
- Loch, S.D., et al.
(författare)
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Influence of long-lived metastable levels on the electron-impact single ionization of C2
- 2005
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 71:1, s. 012716-1
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Magnuson, Martin, et al.
(författare)
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Competition between decay and dissociation of core-excited carbonyl sulfide studied by x-ray scattering
- 1999
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 59:6, s. 4281-4287
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Böhm, S, et al.
(författare)
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Influence of electromagnetic fields on the dielectronic recombination of Ne7+ ions
- 2001
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947. ; 64:3, s. 032707/1-032707/7
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Glans, Peter, et al.
(författare)
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Determination of the lifetime width of the argon L1-hole state
- 1993
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Ingår i: Physical Review A (Atomic, Molecular, and Optical Physics). - 1050-2947. ; 47:2, s. 1539-1542
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Glans, Peter, et al.
(författare)
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Dielectronic recombination of N4
- 2001
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947. ; 649:4, s. 043609/1-043609/11
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Gunnelin, K, et al.
(författare)
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Assigning x-ray absorption spectra by means of soft-x-ray emission spectroscopy
- 1998
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947. ; 57:2, s. 864-872
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- LaVilla, R.E., et al.
(författare)
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Additional features in the 3d-4p x-ray-emission spectrum of Xe
- 1994
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Ingår i: Physical Review A - Atomic, Molecular, and Optical Physics. - 1050-2947. ; 49:3, s. 2185-2187
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
- Skytt, P, et al.
(författare)
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Lifetime-vibrational interference effects in the resonantly excited x-ray-emission spectra of CO
- 1997
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947. ; 55:1, s. 146-154
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 9. |
- Skytt, P, et al.
(författare)
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Role of screening and angular distributions in resonant x-ray emission of CO
- 1997
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947. ; 55:1, s. 134-145
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Tokman, M, et al.
(författare)
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Dielectronic recombination resonances in F6
- 2002
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Ingår i: Physical Review A - Atomic, Molecular, and Optical Physics. - 1050-2947. ; 66:1, s. 012703/1-012703/13
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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