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

Abstract

Context. Emission and absorption features from C-like ions serve as temperature and density diagnostics of astrophysical plasmas. R-matrix electron-impact excitation data sets for C-like ions in the literature merely cover a few ions, and often only for the ground configuration. Aims. Our goal is to obtain level-resolved effective collision strength over a wide temperature range for C-like ions from N ii to Kr xxxi (i.e., N + to Kr 30+ ) with a systematic set of R-matrix calculations. We also aim to assess their accuracy. Methods. For each ion, we included a total of 590 fine-structure levels in both the configuration interaction target and close-coupling collision expansion. These levels arise from 24 configurations 2l 3 nl with n = 2 − 4, l = 0 − 1, and l = 0 − 3 plus the three configurations 2s 2 2p5l with l = 0 − 2. The AUTOSTRUCTURE code was used to calculate the target structure. Additionally, the R-matrix intermediate coupling frame transformation method was used to calculate the collision strengths.Results. We compare the present results of selected ions with archival databases and results in the literature. The comparison covers energy levels, transition rates, and effective collision strengths. We illustrate the impact of using the present results on an Ar xiii density diagnostic for the solar corona. The electron-impact excitation data is archived according to the Atomic Data and Analysis Structure (ADAS) data class adf04 and will be available in OPEN-ADAS. The data will be incorporated into spectral codes, such as CHIANTI and SPEX, for plasma diagnostics.

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

“…We adopted the same approach for the structure and collision calculations, described in Section 2.1 and Section 2.2, as detailed in Mao et al (2020) for C-like ions. The main difference for N-like ions is that we included a total of 725 fine-structure levels in both the configuration-interaction target expansion and the close-coupling collision expansion.…”

“…We use the Thomas-Fermi-Dirac-Amaldi model for the electronic potential. The nl-dependent scaling parameters (Nussbaumer, & Storey 1978) are obtained following the procedure presented in Mao et al (2020) without manual re-adjustment. This ensures that we do not introduce arbitrary changes across the iso-electronic sequence.…”

“…In terms of R-matrix electron-impact excitation data, systematic calculations for many iso-electronic sequences (Li-, Be-, B-, F-, Ne-, Na-, and Mg-like) have been performed over the past decade (see Badnell et al 2016 for a review, andMao et al 2020 for the most recent C-like one). When R-matrix data are not available, then either interpolated data, from adjacent ions in the same iso-electronic sequence, or less accurate distorted wave data are used, if available.…”

“…Following systematic intermediate coupling frame transformation (ICFT) R-matrix calculations for C-like ions (Mao et al 2020), here we present similar calculations for N-like ions from N ii to Zn xxiv (i.e. N + to Zn 23+ ).…”

Atomic Data for Plasma Spectroscopy: The CHIANTI Database, Improvements and Challenges

“…A list of recent UK APAP network calculations is given in [22]. In addition, CE rates for all the ions in the C-like [27] and N-like sequences (Mao et al, in preparation) have recently been calculated. Plans are in place to calculate the ions in the O-like sequence, and in the future the H-and He-like ions.…”