Direct determination of the energy of the first excited fine-structure level in Ba6+

Abstract

We present an experimental observation of the visible magnetic dipole transition between the fine structure levels in the ground term of ${\mathrm{Ba}}^{6+}$ ($5s{\phantom{\rule{0.16em}{0ex}}}^{2}5{p}^{2}$: $^{3}P_{0}\ensuremath{-}^{3}P_{1}$) with a compact electron beam ion trap. The wave number in vacuum of the transition is determined to be 15505.506(37) ${\mathrm{cm}}^{\ensuremath{-}1}$ by simultaneously observing the reference lines of neutral Ne. The present measurement reduces the uncertainty in the previously reported value obtained from observation of the electric dipole transitions to the ground terms in the extreme ultraviolet range [Phys. Scr. 46, 403 (1992)].