The spectrum and term system for helium-like boron, B IV

The spectrum of the helium-like boron ion B IV has been obtained by using the laser-impact technique. It has been recorded in the 250-4500 AA wavelength region. The ionization energy has been determined to be 2091976+or-20 cm -1 , by means of the theoretical values for the np 1 P energy levels. Experimental values of the Lamb shift have been determined for the ground state (-93+or-20 cm -1 ) and for the two first excited levels 2s 1 S and 2s 3 S (-8.0 cm -1 and -8.6 cm -1 respectively). The term system is derived from twenty two new lines and extended by using Ritz formulae and other semi-empirical formulae. The results are compared with theoretical calculations of ionization energies.