Breit PauliR-matrix calculations for electron impact excitation of Fe XVII: a benchmark study

Abstract

Abstract.A comprehensive study of relativistic and resonance effects in electron impact excitation of (e+Fe XVII) is carried out using the Breit-Pauli R-matrix (BPRM) method in the relativistic close coupling (CC) approximation.Two sets of eigenfunction expansions are employed; first, up to the n = 3 complex corresponding 37 fine-structure levels (37CC) from 21 LS terms; second, up to the n= 4 corresponding to 89 fine-structure levels (89CC) from 49 LS terms. In contrast to previous works, the 37CC and the 89CC collision strengths exhibit considerable differences. Denser and broader resonances due to n= 4 are present in the 89CC results both above and below the 37 thresholds, thus significantly affecting the collision strengths for the primary X-ray and EUV transitions within the first 37 n= 3 levels. Extensive study of other effects on the collision strengths is also reported: (i) electric and magnetic multipole transitions E1,E2,E3 and M1,M2, (ii) J-partial wave convergence of dipole and non-dipole transitions, (iii) high energy behaviour compared to other approximations. Theortical results are benchmarked against experiments to resolve longstanding discrepancies -collision strengths for the three prominent X-ray lines 3C, 3D and 3E at 15.014, 15.265, and 15.456Å are in good agreement with two independent measurements on Electron-Beam-Ion-Traps (EBIT). Finally, line ratios from a collisional-radiative model using the new collisional rates are compared with observations from stellar coronae and EBITs to illustrate potential applications in laboratory and astrophysical plasmas.

R-matrix electron-impact excitation data for the Ne-like iso-electronic sequence

“…The present result is also in agreement (8%) with that reported by Aggarwal et al (2003), see the point at E e = 1020 eV. The resulting effective collision strengths also show good agreement (about 7%) between the present results and the BPRM of Chen et al (2003) and darc of Loch et al (2006) over temperatures of equilibrium abundance for Fe 16+ . With decreasing electron temperature, the difference between the present results and the DW plus isolated resonance results of Landi & Gu (2006) increases, but is still less than 20% at T e = 2.9 × 10 5 K. The darc results of Chen (2007) are slightly lower than the present ones, by about 10%.…”

“…-Fe 16+ Many calculations have been done with resonances taken into account, such as the serial work of Chen et al (2003, Chen (2007), Aggarwal et al (2003), Loch et al (2006), and Landi & Gu (2006). In Fig.…”

“…However, the atomic structure and electronimpact excitation (EIE) of Ne-like ions are extremely complex, which results in there being large uncertainties in line intensity ratios (2p 5 3d 1 P 1 → 2p 6 1 S 0 vs 2p 5 3d 3 D 1 → 2p 6 1 S 0 , this is usually designated 3C/3D, as well as 3s − 2p vs. 3C) between measurements or observations and predictions (Beiersdorfer et al 2001(Beiersdorfer et al , 2002Gu et al 2004). For example, even for iron, EIE of this ion has been investigated experimentally and theoretically for a long time (Smith et al 1985;Chen et al 2003;Loch et al 2006;Beiersdorfer et al 2001, 2002 andreferences therein).…”

“…Recently, there have been several works using this method for three ions in this iso-electronic sequence. Chen et al (2003) performed (BPRM) Breit-Pauli R-matrix (Berrington et al 1995) calculations for Fe 16+ with an 89 fine-structure level close-coupling expansion (to n = 4). Loch et al (2006) performed a fully-relativistic larger scale Fe 16+ calculation (139 fine-structure levels, including an additional 50 levels of the 2p 5 5l configurations) using the Dirac atomic R-matrix code (darc, Norrington & Grant 1987).…”

Benchmarking atomic data for astrophysics: Fe XVII X-ray lines

“…An approximate treatment of the resonances in the collision strengths was included in Gu's work. In the past few years, a few R-matrix calculations have been performed by Aggarwal et al (2003), Chen et al (2003), Loch et al (2006), and more recently by Liang & Badnell (2010) as part of the UK APAP network 1 .…”