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

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 Å) and grating spectra of Nd vacuum sliding sparks were recorded within the regions 820-1159 Å and 1600-3250 Å. 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 Å 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 $178,090\pm 330$ cm${}^{-1}$, doubling the accuracy of the previously published value.

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