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Toward Calculations with Spectroscopic Accuracy: the 2s2.2p 2Po_{3/2} - 2s2p2 4P_{5/2} Excitation Energy in Boron

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 iso-electronic sequence for the 2s2.2p 2Po_{3/2} - 2s2p2 4P_{5/2} transition. In this paper, accurate theoretical excitation energies from a newly developed 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, 28959 +/- 5 cm^{-1}, is in better agreement with the values obtained by Edlén 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