Overview of recent advances performed in the study of atomic structures and radiative processes for the lowest ionization stages of heavy elements

Abstract

During the past 20 years, part of our work has been focused on the study of the atomic structure and the determination of radiative parameters in neutral and slightly ionized heavy atoms (Z ≥ 37). These elements attracted little previous interest because of the complexity of their electronic structures, the poor knowledge of their spectra, and the difficulty to perform experimental measurements. They present, however, great interest in the development of other scientific areas, such as astrophysics and plasma physics. In this paper, we give an overview of the recent progress performed by the group of Atomic Physics and Astrophysics at Mons University (Belgium) in the theoretical modelling and the experimental analysis of such heavy elements. We also discuss some applications of the atomic data obtained in our work for the interpretation of the spectra observed from astrophysical and laboratory plasmas.Key words: atomic data, oscillator strengths, radiative transition probabilities, heavy elements.Résumé : Durant les 20 dernières années, une partie de notre travail a été focalisée sur l'étude de la structure atomique et la détermination des paramètres radiatifs dans les atomes lourds neutres et faiblement ionisés (Z ≥ 37). Ces éléments avaient attiré peu d'intérêt auparavant à cause de la complexité de leurs structures électroniques, du manque de connaissance de leurs spectres et de la difficulté à réaliser des mesures expérimentales. Ils présentent cependant un grand intérêt pour le développe-ment d'autres domaines scientifiques comme l'astrophysique et la physique des plasmas. Dans cet article, nous présentons un aperçu général des progrès récents réalisés par le groupe de Physique Atomique et Astrophysique de l'Université de Mons (Belgique) dans la modélisation et l'analyse expérimentale de tels éléments lourds. Nous discutons également quelques applications des données atomiques obtenues dans notre travail pour l'interprétation des spectres observés à partir de plasmas astrophysiques et de laboratoire.Mots-clés : ions lourds, données atomiques, temps de vie radiatifs, forces d'oscillateur, probabilités de transition.

Radiative Decay Rates for Electric Dipole, Magnetic Dipole and Electric Quadrupole Transitions in Triply Ionized Thulium (Tm IV)

“…However, as in the case of our previous analysis related to Er III, such core-polarization corrections were not considered in the atomic orbital calculation of the ground configuration 4f 12 . The 4f electrons being indeed located deep inside the Xe-like 5s 2 5p 6 ionic core, the analytical polarization corrections to the dipole operator as introduced in our model [25][26][27] are no longer valid for transitions involving these electrons. As an alternative, the uncorrected <4f|r|5d> radial matrix element corresponding to the 4f 12 -4f 11 5d transitions was scaled down by a factor 0.81, as we proceeded for Er III [24].…”

“…More precisely, the configuration sets explicitly retained for the computations were 4f 12 , 4f 11 6p, 4f 11 7p, 4f 11 5f, 4f 11 6f for the even parity, and 4f 11 6s, 4f 11 7s, 4f 11 5d, 4f 11 6d, 4f 11 7d for the odd parity. The core-valence interactions were included by means of a core-polarization pseudo-potential and a correction to the dipole operator according to the procedure described in many of our previous papers (see e.g., [25][26][27]). As a reminder, for atomic systems with n valence electrons, this core-polarization potential gives rise to the following one-particle, V P1 , and two-particle, V P2 , contributions:…”

Calculated oscillator strengths for the strongest lines of cosmochronological interest in the visible spectrum of singly ionized uranium (U II)

“…It is worth noting however that, three of these Comparison between experimental and theoretical strongest emission lines in U II. Only visible spectral lines observed by Palmer et al (1980) with measured intensities greater than 10 (top figure) and those calculated in this work with weighted transition probabilities, gA, larger than 10 7 s −1 (bottom figure) are shown.…”

“…In their critical compilation related to actinides, Blaise & Wyart (1992) listed some preliminary U II energy levels, using the emission lines listed by Steinhaus et al (1971) and Palmer, Keller & Engleman (1980), thus updating the previous estimates published by Brewer (1971). An uranium hollow-cathode Fourier transform spectrum between 1800 and 42 000cm −1 was then combined with previous visible and ultraviolet spectra by Blaise et al (1994) who were able to determine the numerical values for 354 and 809 energy levels belonging to the four odd configurations 5f 3 7s 2 , 5f 3 6d7s, 5f 3 6d 2 , 5f 4 7p, and to the six even configurations 5f 4 7s, 5f 4 6d, 5f 2 6d 2 7s, 5f 2 6d7s 2 , 5f 3 7s7p, 5f 3 6d7p, respectively.…”

“…As regards the radiative decay rates, the first measurements of relative line intensities in U II were obtained from emission arc spectra by Meggers et al (1961), Corliss and Bozman (1962), Voigt (1975), and Corliss (1976). In the atlas of uranium lines published by Palmer et al (1980), relative intensities were listed for 4928 U I and 431 U II emission spectral lines between 11 000 and 26 000cm −1 . The oscillator strengths of the lines at λ = 3859.571 Å and λ = 4050.041 Å were later determined by Chen & Borzileri (1981) who combined experimental lifetime measurements of the upper levels with unpublished branching fractions.…”