Accurate and experimentally validated transition data for Si I and Si II^★

¹ Materials Science and Applied Mathematics, Malmö University, 205 06 Malmö, Sweden
e-mail: asli.pehlivan@mau.se, henrik.hartman@mau.se
² Division of Astrophysics, Department of Physics, Lund University, 221 00 Lund, Sweden

Received: 14 December 2022
Accepted: 5 July 2023

Abstract

Aims. The aim of this study is to provide radiative data for neutral and singly ionised silicon, in particular for the first experimental oscillator strengths for near-infrared Si I lines. In addition, we aim to perform atomic structure calculations both for neutral and singly ionised silicon while including lines from highly excited levels.

Methods. We performed large-scale atomic structure calculations with the relativistic multiconfiguration Dirac-Hartree-Fock method using the GRASP2K package to determine log(𝑔ƒ) values of Si I and Si II lines, taking into account valence-valence and core-valence electron correlation. In addition, we derived oscillator strengths of near-infrared Si I lines by combining the experimental branching fractions with radiative lifetimes from our calculations. The silicon plasma was obtained from a hollow cathode discharge lamp, and the intensity-calibrated high-resolution spectra between 1037 and 2655 nm were recorded by a Fourier transform spectrometer.

Results. We provide an extensive set of accurate experimental and theoretical log(𝑔ƒ) values. For the first time, we derived 17 log(𝑔ƒ) values of Si I lines in the infrared from experimental measurements. We report data for 1500 Si I lines and 500 Si II lines. The experimental uncertainties of our ƒ-values vary between 5% for the strong lines and 25% for the weak lines. The theoretical log(𝑔ƒ) values for Si I lines in the range 161 nm to 6340 nm agree very well with the experimental values of this study and complete the missing transitions involving levels up to 3s²3p7s (61 970 cm⁻¹). In addition, we provide accurate calculated log(𝑔ƒ) values of Si II lines from the levels up to 3s²7f (122 483 cm⁻¹) in the range 81 nm to 7324 nm.