Doublet-quartet energy separation in boron : a partitioned-correlationfunction- interaction method

No lines have been observed for transitions between the doublet and quartet levels of B i. Consequently, energy levels based on observation for the latter are obtained through extrapolation of wavelengths along the isoelectronic sequence for the $2{s}^{2}2p$ ${\phantom{\rule{0.16em}{0ex}}}^{2}{P}_{3/2}^{o}$ -- $2s2{p}^{2}$ ${\phantom{\rule{0.16em}{0ex}}}^{4}{P}_{5/2}$ transition. In this paper, accurate theoretical excitation energies from a partitioned-correlation-function-interaction (PCFI) method are reported for B i that include both relativistic effects in the Breit-Pauli approximation and a finite mass correction. Results are compared with extrapolated values from observed data. For B i our estimate of the excitation energy 28 959 $\ifmmode\pm\else\textpm\fi{}$ 5 cm${}^{\ensuremath{-}1}$ is in better agreement with the values obtained by Edl\'en et al. (1969) than those reported by Kramida and Ryabtsev (2007). Our method is validated by applying the same procedure to the separation of these levels in C ii.