Interference effects in the photorecombination of argonlikeSc3+ions: Storage-ring experiment and theory

Abstract

Absolute total electron-ion recombination rate coefficients of argonlike Sc 3+ (3s 2 3p 6 ) ions have been measured for relative energies between electrons and ions ranging from 0 to 45 eV. This energy range comprises all dielectronic recombination resonances attached to 3p→3d and 3p→4s excitations. A broad resonance with an experimental width of 0.89 ± 0.07 eV due to the 3p 5 3d 2 2 F intermediate state is found at 12.31 ± 0.03 eV with a small experimental evidence for an asymmetric line shape. From R-Matrix and perturbative calculations we infer that the asymmetric line shape may not only be due to quantum mechanical interference between direct and resonant recombination channels as predicted by Gorczyca et al. [Phys. Rev. A 56, 4742 (1997)], but may partly also be due to the interaction with an adjacent overlapping DR resonance of the same symmetry. The overall agreement between theory and experiment is poor. Differences between our experimental and our theoretical resonance positions are as large as 1.4 eV. This illustrates the difficulty to accurately describe the structure of an atomic system with an open 3d-shell with state-of-the-art theoretical methods. Furthermore, we find that a relativistic theoretical treatment of the system under study is mandatory since the existence of experimentally observed strong 3p 5 3d 2 2D and 3p 5 3d4s 2 D resonances can only be explained when calculations beyond LS-coupling are carried out.

Dielectronic recombination of argon-like ions

“…2 have been analyzed more fully in our earlier studies of Sc iv (Nikolić et al 2010) and Ti v (Nikolić et al 2009), but the following points should be made. First, there is experimental data available for both of these ions (Schippers et al 1998(Schippers et al , 2002, and these measurements were useful for quantifying the positions of low-energy resonances. However, the experiments for these low-charged Ar-like ions were subject to motional Stark effect that reionized the higher-n recombined bound Schippers et al (1998Schippers et al ( , 2002; (b) black doted curve, compilation by Landini & Fossi (1991); (c) black dash-dotted curve, empirical formula of Hahn (1991); (d) black solid curve, recommended value by Mazzotta et al (1998); (e) black dashed curve, empirical results of Mewe et al (1980).…”

Atomic data for neutron-capture elements

“…comm. ;Schippers et al 2002). Thus, experimental DR measurements of low-charge Se ions are extremely difficult if not impossible with existing storage ring facilities.…”

“…Unfortunately, it is extremely challenging to use storage ring experiments to measure DR rate coefficients of low charge-to-mass species such as the Se ions investigated in this paper. The lowest charge-to-mass ion whose recombination rate coefficient has been experimentally determined is Sc 3+ , with q/m = 1/15 (Schippers et al 2002). The maximum bending power of the dipole magnets on current storage ring facilities is the limiting factor for low q/m species, which cannot be stored at sufficiently high energies.…”

Time-reversal Studies in Photorecombination and Photoionization Experiments with Ion Beams

“…Photon energy ( eV ) FIGURE 3. Experimental cross sections for PI of Sc 2· a) [11] and PR of Sc 3· ions c) [12]. Most of the detected resonances are identified at the state-to-state level as indicated in the different panels.…”

“…The application of detailed balance to experiments on PI of Sc 2· [11] and PR of Sc 3· [12] 2 and Mg 3p 5 3d4s, both based on a Mg-like core. Both configurations support states with very fast autoionization decay and, hence, many of the associated resonances are broad.…”