ENERGY LEVELS OF NEUTRAL BERKELIUM - 249Bk l
In the first report on the observation of the berkelium 249Bk spark spectrum in 1965 (65.2), 20 lines were given without ion assignment. The nuclear spin l = 7/2 of this isotope was determined from two lines with resolved hyperfine structures, but in these spectra emitted by electrodeless discharge lamps, several thousands of lines were measurable in the range 250-900 nm (67.3). Their systematic measurement led to a list of 1930 lines characterized by observed intensities and wavelengths, hyperfine widths and Zeeman structures, combining levels when known (78.1).
These data were completed by infrared observations by means of Fourier transform spectroscopy at Laboratoire Aimé Cotton, and a list of the strongest 90 lines, 76 of which classified, was published (77.5).
The preliminary-analysis of (78.1) was revised and extended to include now 179 odd and 186 even levels of Bk I (87.2). Due to the rarity of berkelium isotopes other than 249Bk, the configuration assignments are based only on empirical considerations on intensities and g-factors, and on the Slater-Condon type parametric study of the two lowest configurations. Fourteen levels are attributed to the ground configuration 5f97s2, as part of systematic analyses of 5fN7s2 (80.4). Four other odd configurations have been located and their lowest levels, at 17182 cm-1 for 5f96d7s, 17777 cm-1 for 5fN7s27p, 24652 cm-1 for 5f8d7s7p and 32488 cm-1 for 5f97s8s, are in agreement with earlier predictions (71.1). In the even parity, the preliminary study of 5f86d7s2 on a complete basis set (unp.1), helped identifying the lowest levels by means of calculated energies and hyperfine structure constants. Three higher even configurations, 5f97s7p, 5f86d27s and 5f96d7p which start respectively at 16913, 21506 and 36952 cm-1, have been labelled empirically.