Term analysis of complex spectra: New experimental data for Fe II

The term analysis of spectra of iron group elements at low ionization stages is discussed. This group of complex spectra are line-rich due to a complicated atomic structure. The practical treatment of the spectral data is discussed in terms of numerical and analytical procedures. Besides the use of traditional techniques in the analysis we have gained information from intensity comparisons. The method of analysis is applied to hollow-cathode spectra of iron with different carrier gases and different discharge modes recorded by means of Fourier transform spectrometers and grating instruments. In four subconfigurations of Fe II, 3d6(3L)4d, where 3L = 3P, 3F, 3G and 3H, we have found about seventy new levels, which show strong mixing as predicted by theoretical calculations. A strong 4d ↔ 5d interaction is observed as well as accidental coincidences of levels. (orig.)