| 1. |
- Ali, Safdar, et al.
(författare)
-
Electron-ion recombination rate coefficients for C II forming C I
- 2012
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 753:2, s. 132-
-
Tidskriftsartikel (refereegranskat)abstract
- We have determined absolute dielectronic recombination rate coefficients for C II, using the CRYRING heavy-ions storage ring. The resonances due to 2s-2p (∆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 103-106 K. The derived temperature dependent plasma recombination rate coefficients are presented graphically to compare with the theoretical data available in literature and parameterized by using a fit formula for convenient use in plasma modelling codes. In the temperature range of 103-2×104 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 2×104 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.
(författare)
-
Tunable excitation x-ray-fluorescence spectroscopy in phase-analysis of high-Tc superconductors
- 1994
-
Ingår i: Journal of physics-condensed matter. - 0953-8984. ; 6:43, s. 9267-9274
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
(författare)
-
Enhancement of dielectronic recombination by external electromagnetic fields
- 2003
-
Ingår i: Hyperfine Interactions. - 0304-3843. ; 146-147:1-4, s. 23-27
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 4. |
- Böhm, S, et al.
(författare)
-
Experimental NV and NeVIII low-temperature dielectronic recombination rate coefficients
- 2005
-
Ingår i: Astronomy & Astrophysics. - 0004-6361. ; 437:3, s. 1151-1157
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 5. |
- Böhm, S, et al.
(författare)
-
Influence of electromagnetic fields on the dielectronic recombination of Ne7+ and O5+ ions
- 2001
-
Ingår i: Physica Scripta. Topical Issues. - 0281-1847. ; T92, s. 395-397
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 6. |
- Böhm, S, et al.
(författare)
-
Influence of electromagnetic fields on the dielectronic recombination of Ne7+ ions
- 2001
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947. ; 64:3, s. 032707/1-032707/7
-
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.
|
|
| 7. |
- Cesar, A, et al.
(författare)
-
Resonant x-ray scattering beyond the Born-Oppenheimer approximation: Symmetry breaking in the oxygen resonant x-ray emission spectrum of carbon dioxide
- 1997
-
Ingår i: Journal of Chemical Physics. - 0021-9606. ; 106:9, s. 3439-3456
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
(författare)
-
Electric-octupole and pure-electric-quadrupole effects in soft-X-ray photoemission
- 2000
-
Ingår i: Physical Review Letters. - 0031-9007. ; 84:10, s. 2116-2119
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
(författare)
-
Breakdown of the independent particle approximation in high-energy photoionization
- 1997
-
Ingår i: Physical Review Letters. - 0031-9007. ; 78:24, s. 4553-4556
-
Tidskriftsartikel (refereegranskat)abstract
- 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. |
- Ekengard, Erik, et al.
(författare)
-
Antimalarial activity of ruthenium(ii) and osmium(ii) arene complexes with mono- and bidentate chloroquine analogue ligands.
- 2015
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9234 .- 1477-9226. ; 44:44, s. 19314-19329
-
Tidskriftsartikel (refereegranskat)abstract
- Eight new ruthenium and five new osmium p-cymene half-sandwich complexes have been synthesized, characterized and evaluated for antimalarial activity. All complexes contain ligands that are based on a 4-chloroquinoline framework related to the antimalarial drug chloroquine. Ligands are salicylaldimine derivatives, where = N-(2-((2-hydroxyphenyl)methylimino)ethyl)-7-chloroquinolin-4-amine, and contain non-hydrogen substituents in the 3-position of the salicylaldimine ring, viz. F, Cl, Br, I, NO2, OMe and (t)Bu for , respectively. Ligand is also a salicylaldimine-containing ligand with substitutions in both 3- and 5-positions of the salicylaldimine moiety, i.e. N-(2-((2-hydroxy-3,5-di-tert-butylphenyl)methyl-imino)ethyl)-7-chloroquinolin-4-amine, while is N-(2-((1-methyl-1H-imidazol-2-yl)methylamino)ethyl)-7-chloroquinolin-4-amine) The half sandwich metal complexes that have been investigated are [Ru(η(6)-cym)()Cl] (Ru--Ru-, cym = p-cymene), [Os(η(6)-cym)()Cl] (Os--Os-, Os-, and Os-), [M(η(6)-cym)()Cl2] (M = Ru, Ru-; M = Os, Os-) and [M(η(6)-cym)()Cl]Cl (M = Ru, Ru-; M = Os, Os-). In complexes Ru--Ru- and Ru-, Os--Os-, Os- and Os- and Os-, the ligands were found to coordinate as bidentate N,O- and N,N-chelates, while in complexes Ru- and Os-, monodentate coordination of the ligands through the quinoline nitrogen was established. The antimalarial activity of the new ligands and complexes was evaluated against chloroquine sensitive (NF54 and D10) and chloroquine resistant (Dd2) Plasmodium falciparum malaria parasite strains. Coordination of ruthenium and osmium arene moieties to the ligands resulted in lower antiplasmodial activities relative to the free ligands, but the resistance index is better for the ruthenium complexes compared to chloroquine. Overall, osmium complexes appeared to be less active than the corresponding ruthenium complexes.
|
|
