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.
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