The absorption spectrum of europium

The europium absorption spectrum has been photographed at high resolution in the spectral region 7200 to 2100 A which includes the entire sharp-line spectrum longward of the first ionization limit. Wavelengths and wavenumbers have been determined by comparison with thorium standards. Since all transitions take place from the ground level the wavenumbers correspond to excitation energies of even-parity levels with total angular momentum (J) of 5/2, 7/2 or 9/2. J-values and gsub(J)-values have been determined for many of these levels from a study of the longitudinal Zeeman effect in the 5 T (50 kG) field of a superconducting solenoid magnet. The configurations 4f7 (8S) 6s 6p, 4f7 (8S) 6s 7p, 4f7 (8S) 5d 6p and 4f6 (7F) 5d 6s2 are discussed in detail. Levels of 4f6 (7F) 5d2 6s and 4f7 (6I) 6s 6p are reported for the first time. Several long series have been discovered among the highly excited levels. Some of these can be identified with levels arising from 4f7 6s (9S) np and 4f7 6s (7S) np but interpretation is complicated by the presence of several perturbations of unknown origin. (author)