Hyperfine structure investigations of atomic niobium with optogalvanic and laser-induced fluorescence spectroscopy in the near-infrared wavelength range

Abstract

Aims. The aim of this work is to increase the amount of hyperfine structure data of atomic niobium (Nb I), which is needed for astrophysicists for the detailed analysis of new stellar spectra. Particular emphasis was placed on the investigation of energy levels with unknown hyperfine structure constants. Methods. The hyperfine structure in the spectrum of Nb I was studied using laser-induced fluorescence spectroscopy and laser optogalvanic spectroscopy with a tuneable single-mode cw Ti:Sa laser in the wavelength range from 750 nm to 865 nm. The Nb atoms were produced and excited in a liquid-nitrogen-cooled hollow-cathode plasma. Results. We measured and analysed 81 spectral lines, 19 of which are not previously known from the literature. In total, the magnetic dipole hyperfine structure constants A were determined for 28 energy levels of even and 53 energy levels of odd parity. The electric quadrupole hyperfine structure constants B were only determined in a few cases, when the spectra were clearly resolved and/or when a level was found from several transitions. The magnetic dipole hyperfine structure constants A of 13 even and 11 odd levels as well as the electric quadrupole hyperfine structure constants B of 13 even and 17 odd levels are presented for the first time. For the other levels, improved values of hyperfine structure constants are given. Conclusions. The hyperfine structure can have a significant effect on stellar absorption line profiles, and the corresponding abundances can be substantially overestimated if these effects are not taken into account. Therefore, a detailed consideration of the hyperfine structure is important for stellar abundance determinations. The present work substantially increases the knowledge of hyperfine structure of Nb, which plays an important role in investigating the nucleosynthesis of heavy elements.

Investigation of the Hyperfine Structure of Atomic Niobium (Nb I) Spectral Lines Based on the Lower Energy Levels at 22936, 23010, and 23048 cm<sup>-1</sup>

“…but with much lower uncertainty. Finally, we obtain for level 35630 cm −1 A = 551.3(20) MHz, close to the value in ref [18],. since the fixed value of A changed from 82 (4) to 84.7(20) MHz only.…”

“…Then we set the laser wavelength to such a calculated value and searched for a LIF The hf structure constants A of these three even levels are given in ref. [18] to be as follows:…”

“…* value fixed in the fitting procedure; ** in ref. [18], by mistake the A-value of the level at 35344 cm −1 is given as 510.0 (31) MHz. This value belongs to the level at 35156 cm −1 .…”

“…In the last Columns hf constants of the investigated level from literature are given, if available.Since S.K. was co-author of ref [18],. we were interested in how the new results fit to the earlier data evaluation.…”

Parametric study of the fine and hyperfine structure for the even parity configurations of atomic niobium

“…Using laser and radio-frequency spectroscopic methods, the hfs of 31 energy levels of the configurations 4d 4 5s, 4d 3 5s 2 , 4d 5 , 4d 4 5p and 4d 3 5s5p were measured by Fraenkel et al [5]. Doppler-limited optogalvanic spectroscopy was applied in different wavelength ranges by Singh and Rao in 1989 [6], by Singh and Thareja in 1992 [7], by Bouzed et al in 2003 [8], Kröger et al in 2007 [9], and Başar et al in 2013 [10]. Doppler-reduced saturation spectroscopy was performed in the spectral region of 645 nm-675 nm by Başar et al in 2008 [11].…”