Accurate CI-MBPT calculation of radiative lifetimes and transition probabilities of neutral lanthanum (La I) odd states with J = 3/2

Abstract

An accurate calculation of radiative lifetimes and transition probabilities of the first 21 odd states with a total angular momentum J = 3/2 was performed for La I using configuration-interaction many-body perturbation theory (CI-MBPT). A technique to obtain correct transition amplitudes was devised for pairs of states with substantial mixing that improved the theoretical accuracy. The results were compared to known experimental and theoretical data for the considered transitions. It has been shown that the transition data calculated with CI-MBPT and with corrections for pairs of mixed states are in good agreement with the latest experimental data of Den Hartog et al, 2015 J. Phys. B: At. Mol. Phys. 48, 155 001, better than other theoretical results. The transition data can find many applications in astrophysics, and the CI-MBPT formalism with mixing correction is applicable to other atoms similar to or more complex than La I.

CI-MBPT and Intensity-Based Lifetime Calculations for Th II

“…Previously this theory was applied to similar atoms [12,13], and transition probabilities of Si I [14], La II [15], and La I [16] were found in excellent agreement with experiment, although some pairs of levels of La I needed to be adjusted to correct the pair-wise mixing. The method for mixing-angle correction was developed for strong mixing of two pairs of levels, but in general, more levels can strongly interact, which is the case of Th II.…”

“…These particular states were chosen for the following reason. First, J = 1.5 odd states were chosen because they have significant mixing of more than 2 states (see Table 2), so our previous method based on one mixing angle to improve La I transitions for pairs of mixed states [16] would not work and a more general method had to be developed and demonstrated. Lifetimes for many J = 1.5 odd Th II states were precisely measured [6] and constitute a test of the theory.…”

Relativistic Configuration-Interaction and Perturbation Theory Calculations for Heavy Atoms

“…Although La I is quite similar to La II in terms of valence-core interactions, calculations of La I transitions are more challenging [3]. There are many cases of closely spaced levels of the same symmetry which are strongly mixed.…”

“…This interaction cannot be ignored and needs to be treated beyond the second order in many-body perturbation theory (MBPT), if the calculations are carried out in the CI-MBPT framework. Here, several options exist for improvement of accuracy: scaling second-order MBPT corrections [1][2][3], including higher-order effects as in CI-all-order approach [4,5], or including upper core electrons into the valence space [6]. (3) Relativistic effects are significant and lead to deviation from the LS coupling scheme.…”

“…Here, several options exist for improvement of accuracy: scaling second-order MBPT corrections [1][2][3], including higher-order effects as in CI-all-order approach [4,5], or including upper core electrons into the valence space [6]. (3) Relativistic effects are significant and lead to deviation from the LS coupling scheme. Because, for example, electric-dipole transitions conserve the total spin in non-relativistic approximation, the mixing of states of different S has a strong effect on the magnitude of the electric dipole transitions and is one reason for large uncertainty in the computed values.…”