Energy levels for Th I were computed from the weighted averages of wavelengths from seven sets of published interferometrically measured data. The most self-consistent energy levels obtained in this way were then employed to calculate wavenumbers that have a standard deviation of less than 10 mK. We propose that these lines be adopted as class-B secondary standards. Calculated wavelengths of 1375 Th I lines and weighted averages of 181 interferometrically measured Th I and Th II lines between 2565 and 12 381 Å are given.
A. GIACCHETTI, R. W. STANLEY, and R. ZALUBAS, "Proposed Secondary-Standard Wavelengths in the Spectrum of Thorium," J. Opt. Soc. Am. 60, 474-489 (1970)