The Spectrum of Thorium from 250 nm to 5500 nm: Ritz Wavelengths and Optimized Energy Levels

TL;DR

This study provides highly accurate Ritz wavelengths and optimized energy levels for thorium across a broad spectral range, improving calibration standards for spectroscopic applications.

Contribution

It introduces a comprehensive re-optimization of thorium energy levels and Ritz wavelengths using new high-resolution data combined with previous line lists, correcting past errors.

Findings

Calculated 19874 Ritz wavelengths between 250 nm and 5500 nm.

Identified and corrected systematic errors in previous thorium line lists.

Discovered 102 new thorium energy levels.

Abstract

We have made precise observations of a thorium-argon hollow cathode lamp emission spectrum in the region between 350 nm and 1175 nm using a high-resolution Fourier transform spectrometer. Our measurements are combined with results from seven previously published thorium line lists (Giacchetti et al. 1974; Zalubas & Corliss 1974; Zalubas 1976; Palmer & Engleman 1983; Engleman et al. 2003; Lovis & Pepe 2007; Kerber et al. 2008) to re-optimize the energy levels of neutral, singly-, and doubly-ionized thorium (Th I, Th II, and Th III). Using the optimized level values, we calculate accurate Ritz wavelengths for 19874 thorium lines between 250 nm and 5500 nm (40000 1/cm to 1800 1/cm). We have also found 102 new thorium energy levels. A systematic analysis of previous measurements in light of our new results allows us to identify and propose corrections for systematic errors in Palmer & Engleman (1983) and typographical errors and incorrect classifications in Kerber et al. (2008). We also found a large scatter in the thorium line list of Lovis & Pepe (2007). We anticipate that our Ritz wavelengths will lead to improved measurement accuracy for current and future spectrographs that make use of thorium-argon or thorium-neon lamps as calibration standards.