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

Abstract

Aims. Emission lines from ions in the Mg-like iso-electronic sequence can be used as reliable diagnostics of temperature and density of astrophysical and fusion plasmas over a wide range of parameters. Data in the literature are quite lacking, there are no calculations for many of the ions in the sequence. Methods. We have carried-out intermediate coupling frame transformation R-matrix calculations which include a total of 283 finestructure levels in both the configuration interaction target and close-coupling collision expansions. These arise from the configurations 1s 2 2s 2 2p 6 3{s, p, d} nl with n = 4, 5, and for l = 0−4. Results. We obtain ordinary collision strengths and Maxwell-averaged effective collision strengths for the electron-impact excitation of all the ions of the Mg-like sequence, from Al + to Zn 18+ . We compare our results with those from previous R-matrix and distorted waves calculations, where available, for some benchmark ions. We find good agreement with the results of previous calculations for the transitions n = 3−3. We also find good agreement for the most intense transitions n = 3−4. These transitions are important for populating the upper levels of the main diagnostic lines.

Resolution of the forbidden (J= 0 → 0) excitation puzzle in Mg-like ions

“…(1) and is said to be a unitarized DW method when it does so, this is sometimes referred to as the strong coupling DW approximation. We speculated (Fernández-Menchero et al 2014b) that this might be the source of the differences in weak collision strengths for forbidden J − J = 0-0 transitions since the use of Eq. (1) treats the close coupling as a perturbation within the DW method (Seaton 1961), while the use of Eq.…”

“…In a recent paper (Fernández-Menchero et al 2014b), we used the intermediate coupling frame transformation R-matrix method to calculate electron-impact excitation data for all ions of the Mg-like isoelectronic sequence from Al + to Zn 18+ for all transitions involving levels up to principal quantum number n = 5. We also carried out distorted-wave (DW) calculations using the code autostructure (AS; Badnell 2011) and exactly the same atomic structure as we used for the R-matrix calculations.…”

Benchmarking atomic data for astrophysics: Si iii

“…The outer region calculation used the ICFT method (Griffin et al 1998) and our standard assumptions and codes (see the APAP website). Details on the calculation can be found in Fernández-Menchero et al (2014). The thermally-averaged (effective) collisions strength Υ(i− j) were calculated by assuming a Maxwellian electron distribution and linear integration with the final energy of the colliding electron.…”

“…This is done here by carrying out new atomic calculations and then reassessing the diagnostics using various solar and stellar observations. The scattering calculations are part of our UK APAP network work along the Mg-like sequence (Fernández-Menchero et al 2014).…”

MCDHF and RCI calculations of energy levels, lifetimes and transition rates for3l3l′,3l4l′, and3s5lstates in Ca IX – As XXII and Kr XXV

“…In addition to the calculations above, see for example, Safronova et al (2000), Froese Fischer et al (2006), Massacrier & Artru (2012), Hu et al (2014), Si et al (2015), Santana & Träbert (2015). The most recent R-matrix calculations for the Mg-like ions include both collisional and radiative data (Fernandez-Menchero et al 2014). Some of the calculations above provided data only for levels in the n = 3 complex but, as pointed out by Landi (2011), the real need is for data involving configurations with n ≥ 4.…”