Wavelengths and Energy Levels of Neutral Manganese (Mn I) Determined Using High-Resolution Fourier Transform and Grating Spectroscopy

TL;DR

This study delivers a substantial advance in neutral manganese atomic data by merging high-resolution Fourier transform and grating spectra from Mn–Ne and Mn–Ar hollow cathode discharges to produce a comprehensive Mn I linelist and a thoroughly optimized energy level structure. Using Ritz-based identifications and an iterative LOPT approach, the authors revise 384 existing Mn I levels, add 18 new levels, and establish 2186 Mn I transitions with uncertainties markedly improved over prior compilations. They also address anomalous hyperfine structure in select terms and carefully calibrate IR FT spectra to eliminate systematic errors, culminating in energy-level uncertainties often at the 10^{-3} cm^{-1} level. The resulting data significantly enhance the precision of Mn I wavelengths and levels, enabling more reliable interpretation of astrophysical spectra under NLTE and 3D conditions. The final Mn I datasets will underpin improved abundance analyses and opacity calculations in stellar atmospheres across a broad wavelength range, with data reserved for peer-reviewed release to ensure database consistency across modelling frameworks.

Abstract

An extensive analysis of the spectrum of neutral manganese has been performed using spectra of manganese-neon and manganese-argon hollow cathode discharges measured using high resolution Fourier transform (FT) and grating spectroscopy over the range 151 - 5112 nm (1956 - 65876 cm-1). Wavelengths for 10426 spectral lines were extracted from the FT spectra, with uncertainties at least an order-of-magnitude lower than previous measurements. Wavelengths for 13397 lines from new grating spectra were determined for spectral regions beyond the FT spectra range or to provide wavelengths for weak transitions not observed in FT spectra. To aid in level identification, selected, previously published grating lines were included in the energy level optimisation, but no levels in this work relied solely on previously published wavelengths. In total, 24237 lines were included in the final spectral linelist, and these were used to identify 2186 Mn I transitions. These classified spectral lines were then used to optimise the values of 384 previously published energy levels of Mn I, with typical uncertainties of a few 10-3 cm-1, again typically an order-of-magnitude improvement in accuracy. Our study then expanded the known energy level structure of Mn I through the establishment of 18 new energy levels, reported here for the first time. In total, 2187 lines and 402 energy levels of Mn I have been determined as a result of our work, marking a substantial advance in the precision of Mn I atomic data which will enable far more accurate analyses of Mn I lines in astrophysical spectra. Please note: The final wavelength and energy level datasets are withheld from this pre-print to ensure that only the peer-reviewed, definitive versions are released. This approach prevents the propagation of duplicate or inconsistent data across widely used atomic databases and modelling frameworks.

Figures (7)

• Figure 1: Original calibration of spectra mjah (left) and meah (right) using Ar2 lines from Liggins_2017. The dotted line in the meah plot shows a linear fit to the $k_{\text{eff}}$ data with a slope of $-6.2\times10^{-12}$ per cm$^{-1}$.
• Figure 2: Recalibration of spectrum mcnh from mjnh for lines with S/N $> 50$.
• Figure 3: Comparisons between previously published grating wavelengths Catalan1964 and FTS wavelengths Liggins2021. Left: Lines with no identified issues. Right: Lines with issues (e.g. hazy, broadened).
• Figure 4: The singly excited system of energy levels in Mn1.
• Figure 5: The doubly excited system of energy levels in Mn1.