Large-scale Multiconfiguration Dirac–Hartree–Fock Calculations for Astrophysics: Cl-like Ions from Cr viii to Zn xiv

Abstract

We use the multiconfiguration Dirac–Hartree–Fock (MCDHF) method combined with the relativistic configuration interaction approach (GRASP2K) to provide a consistent set of transition energies and radiative transition data for the lower n = 3 states in all Cl-like ions of astrophysical importance, from Cr viii to Zn xiv. We also provide excitation energies calculated for Fe x using the many-body perturbation theory (MBPT, implemented within FAC). The comparison of the present MCDHF results with MBPT and with the available experimental energies indicates that the theoretical excitation energies are highly accurate, with uncertainties of only a few hundred cm−1. Detailed comparisons for Fe x and Ni xii highlight discrepancies in the experimental energies found in the literature. Several new identifications are proposed.

EUV Beam-Foil Spectra of Titanium, Iron, Nickel, and Copper

“…This complexity suggests that the present classifications [59] have to be considered as preliminary until better resolved data of higher statistical reliability and at further time steps become available, as well as accurate computations for all charge states expected. Recent ab initio computations (such as [32][33][34][36][37][38][39][40][41][42][43][44]114]) appear to be on the right path and reach an accuracy that is about an order of magnitude higher than what was available at the time of the beam-foil experiments described here. The measurement problem is further discussed below in the section on Ni.…”

“…There are several more options. Guided by older experimental work on many other elements, the lines of present interest have been found in beam-foil spectra of Cu, too, at wavelengths of 27.480 nm and 29.814 nm, respectively [50], 1% away from the predictions by Wang et al [43]. Evidently, the two experimental wavelengths for the most fundamental transition array (between the ground term and the first excited term) in Cu XIII differ somewhat from even very good recent computations.…”

“…Later work at significantly longer delays (up to some 20 ns, the maximum feasible with the given vacuum chamber size) and at various ion beam energies revealed that the wavelength range from 17 nm to 26 nm comprises the 3p-3d intercombination decays in Si-to Ar-like ions of Ni [119]. The aforementioned newer computations of many of these ions [37][38][39][40][41][42][43][44]114] might support fresh attempts at line classification in delayed spectra of this wavelength range. Moreover, many of the lines in the prompt spectra longwards of the hump can nowadays be identified with information from considerably augmented spectral data bases [11].…”

“…Consequently, in a Cl-like atomic system, one should expect the decays of the lowest (displaced) term, the 3s3p 6 2 S 1/2 level, to the two 3s 2 3p 5 2 P o 3/2,1/2 levels of the ground term, to give rise to prominent lines. According to the computations by Wang et al [43], these lines have wavelengths of 27.175 nm and 29.465 nm, respectively. The calculated upper level lifetime is 148 ps; the wavenumber difference of the two lines is given by the (experimentally known from isoelectronic systems) fine structure interval of the 3s 2 3p 5 2 P o ground term.…”

“…Different approximations and computational approaches yield somewhat different results, resulting in a certain scatter among computational findings. Examples of recent computations on isoelectronic sequences that include ions of present interest (isoelectronic sequences F, Ne, Mg, Si, S) are [32][33][34][35][36][37][38][39][40][41][42][43] and references cited therein. Among the ab initio approaches with the most accurate results are Multireference Møller-Plesset computations of the Ishikawa group, MCDHF computations employing versions of the GRASP code, and RMBPT computations (for unfolding the akronyms and details of the approaches, see a recent review by Jönsson et al [44]).…”