Reference lines in the optogalvanic spectra of uranium and thorium in the wavelength range 422 to 462 nm

The spectra of uranium and thorium are convenient sources of reference lines for wavelength calibration at the level of a few parts in 108. We observed these spectra by laser optogalvanic spectroscopy in commercial hollow-cathode lamps using a single-frequency cw dye laser operating over the wavelength range 422 to 462 nm. Ten uranium and eight thorium lines were measured with an estimated uncertainty of 0.0003 cm−1 by using our Fabry–Perot wavemeter. The results are compared to previous measurements of these lines and are found to be in good agreement with, and 1 order of magnitude more accurate than, values determined by Fourier-transform spectroscopy.