Precision Fe i and Fe ii wavelengths in the ultraviolet spectrum of the iron–neon hollow-cathode lamp

The wave numbers of 167 Fe i lines between 26 000 and 34 100 cm−1 (385–293 nm), 146 Fe i lines between 33 700 and 51 400 cm−1 (297–195 nm), and 221 Fe ii lines between 35 900 and 54 600 cm−1 (279–183 nm) are measured with a relative precision of 30 parts in 109 by Fourier-transform spectrometry. Bridging techniques are used to place the measurements on the same Ar ii–based absolute wave-number scale as previously measured visible spectra. The uncertainty in the absolute wavelengths is limited by small source shifts and the accuracy of the available standards and is estimated to be 0.002 cm−1 (0.008 pm at 200 nm). This is an order of magnitude better than that of the majority of current UV standards.