Transition Probabilities and Oscillator Strengths for E1 Transitions of Ce III

Abstract

The lanthanide elements (Z = 57−71) are important in astrophysics in relation to nucleosynthesis and star formation considerations. Spectroscopic investigations of the doubly ionized elements of this group are motivated by astrophysical interest because, in the hot chemically peculiar (CP) stars, there is an overwhelming presence of lines belonging to the third spectrum which corresponds to the dominant ionization stage [1]. The rare-earth element cerium has a particularly rich, even by rare-earth standards, optical emission spectrum from both its neutral and singly ionized stages. This characteristic has made cerium attractive for use in highintensity discharge light sources where it improves both luminous e cacy and colour rendering [2]. The works for energy levels and lifetimes of doubly ionized cerium (Ce III) can be found in, for example, [3 7]. Many strong lines of cerium in the ultraviolet evidently arise from doubly ionized atoms. King and King published a list of these [8]. Triplet and singlet terms of Ce III were reported by Russell et al. [9]. Observations of the third spectrum of cerium from 757 to 11091 A were given by Sugar [10]. The 4f 4f5d lines of Ce III were measured by Johansson and Litzen [11]. Bord and co-workers calculated oscillator strengths for some Ce III lines [12]. Later, the spectroscopic analysis of Ce III was extended. Wyart and Palmeri gave a list of computed oscillator strengths for some selected transitions [6]. Transition probabilities for Ce III were obtained from branching fractions calculated by Cowan code and experimental lifetimes by Li and co-workers [7]. Biemont et al. emphasized the importance of corepolarization e ects on oscillator strength determination in Ce III [1]. The multicon guration Dirac Fock calculation of the transition energies and oscillator strengths for the 6s S0 6s6p P1, P1 transitions in rare earth