Spectrum and energy levels of the high-lying singly excited configurations of Nd III

TL;DR

This study used advanced spectroscopic techniques and atomic calculations to identify 116 new energy levels and 355 transitions of Nd III, significantly improving the understanding of its atomic structure and energy levels.

Contribution

The paper reports the discovery of 116 previously unknown Nd III energy levels and 355 classified transitions, along with improved atomic data and ionization energy estimation.

Findings

116 new Nd III energy levels identified

355 transitions classified involving new levels

Ionization energy of Nd III refined to 178,090±330 cm$^{-1}$

Abstract

Fourier transform spectra of Nd Penning and hollow cathode discharge lamps were recorded within the region 32,500-54,000 cm$^{-1}$ (3077-1852 {\AA}) and grating spectra of Nd vacuum sliding sparks were recorded within the regions 820-1159 {\AA} and 1600-3250 {\AA}. New energy levels were found using the observed wavelengths measured accurate to a few parts in $10^8$ in Fourier transform spectra and to a few parts in $10^7$ in grating spectra. Atomic structure and transition probability calculations of Nd III were made using the Cowan codes by adjusting energy parameters to fit all known Nd III levels. Nd-rich stellar spectra were also used to evaluate the new calculations. In total, 355 transitions were classified from observed spectra involving 116 previously experimentally unknown energy levels of the 4f$^3$7s, 4f$^3$6d, and 4f$^3$5f configurations of Nd III, all reported here for the first time. One newly identified level of the 4f$^3$5d configuration is also reported. Typical level energy uncertainties are 0.01 cm$^{-1}$ for the 4f$^3$7s and 4f$^3$6d levels and 0.3 cm$^{-1}$ for the 4f$^3$5f levels. In addition, calculated energy levels up to 130,936 cm$^{-1}$ are presented, including eigenvector composition and calculated level lifetimes. Calculated transition probabilities and wavelengths between 1900-50,000 {\AA} are also presented. Using newly established levels of the 4f$^3$7s configuration and the recently established levels of the 4f$^3$6s configuration, the ionisation energy of Nd III was estimated at $178,090\pm330$ cm$^{-1}$, doubling the accuracy of the previously published value.