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The spectrum of singly ionized boron has been studied by using a sliding spark in vacuum. The wavelength list contains 76 lines in the region 9 660-630 Å, 33 of which have not been observed or identified before. The singlets and triplets have been connected by the assumption that 6g 1 G and 6g 3 G have the same term value. The ionization energy has been determined to 202 887.4 ± 1.0 cm-1 by means of the polarization formula for 5g and 6g with a theoretical value of the dipole polarizability. The application of the polarization formula to other members of the Be isoelectronic sequence has lead to an increase by 27.2 cm-1 in the ionization limit of C III. The new value is 386 241.0 ± 1.0 cm-1.

We have undertaken a number of experimental studies of the structure of singly ionized boron, B II. Much of this work was initially motivated by a search for the "missing" 2s3s 1 S term. There was a surprising disagreement between theory and experiment for this level. In this context lots of data for B II were collected over the years, from beam-foil experiments, high-resolution spark spectroscopy and theoretical calculations. The new material, which includes more than 80 newly classified (or revised) spectral lines, has now been thoroughly analyzed. This was followed by a critical compilation of all known levels and lines of B II, along with the theoretical interpretation of the levels, classifications of the lines and calculated transition probabilities for most lines. C Physica Scripta 2005 Physica Scripta 71 A. N. Ryabtsev et al. 3. The beam-foil experiment of 1999 and some earlier unpublished beam-foil studies

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