Theoretical investigation of energy levels and transition for Ce IV^★

¹ Institute of Theoretical Physics and Astronomy, Vilnius University, Saulėtekio Ave. 3, 10257 Vilnius, Lithuania
e-mail: gediminas.gaigalas@tfai.vu.lt; pavel.rynkun@tfai.vu.lt
² Astronomical Institute, Tohoku University, Aoba, Sendai 980-8578, Japan
³ National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, Japan
⁴ Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan

Received: 10 June 2021
Accepted: 16 November 2021

Abstract

Aims. We present extensive energy level and transition data for the Ce IV spectrum. By providing accurate atomic data, we evaluate the impact of atomic data on the opacity in the neutron star merger ejecta.

Methods. We performed energy spectra and transition data calculations using the GRASP2018 package, which is based on the multiconfiguration Dirac–Hartree–Fock and relativistic configuration interaction methods, and the HULLAC code, which is based on a parametric potential method.

Results. We present energy spectra calculated for the 225 levels for the Ce³⁺ ion. Energy levels are compared with recommended values from the NIST Atomic Spectra Database and other available works. The root-mean-square (rms) deviations obtained for the GRASP2018 energy levels of the 5p⁶nl configurations from the NIST data are 1270 cm⁻¹. The rms deviations for the HULLAC results from the NIST data are 5780 cm⁻¹. Furthermore, electric dipole (E1) transition data, line strengths, weighted oscillator strengths, and transition rates are computed between the above levels. The computed transition rates are compared with other theoretical computations. We also evaluate the accuracy of the wave functions and transition parameters by analyzing the dependencies of the line strength S on the gauge parameter G. The gauge dependency method also allows us to determine the transitions for which the ratio between the Babushkin and Coulomb gauges shows real agreement between forms and the transitions for which the agreement between both gauges is random. Using the GRASP2018 and HULLAC data, the opacities in the neutron star merger ejecta are also calculated. We find that the opacity of Ce IV is higher than that presented by previous works, which is because of the higher completeness of our atomic data. Although the differences in the energy levels and transition probabilities cause different features in the opacity spectrum, the Planck mean opacities of both data sets agree within 20%.