Energy difference between the lowest doublet and quartet states states of the boron atom

Abstract

The energies of the lowest $^2P_u$, $^4P_g$ and $2D_g$ states of the boron atom are calculated with $\mu$hartree accuracy, in the basis of symmetrized, explicitly correlated Gaussian lobe functions. Finite nuclear mass and scalar relativistic corrections are taken into account. This study contributes to the problem of the energy differences between doublet and quartet states of boron, which have not been measured to date. It is found that the $^2P_u\rightarrow^4P_g$ excitation energy, recommended in the Atomic Spectra Database, appears underestimated by more than 300~cm$^{-1}$.