On the O ii Ground Configuration Energy Levels

The most accurate way to measure the energy levels for the O II 2 p 3 ground configuration has been from the forbidden lines in planetary nebulae. We present an analysis of modern planetary nebula data that nicely constrain the splitting within the 2 D term and the separation of this term from the ground 4 S 3/2 level. We extend this method to H II regions using high-resolution spectroscopy of the Orion Nebula, covering all six visible transitions within the ground configuration. These data confirm the splitting of the 2 D term while additionally constraining the splitting of the 2 P term. The energies of the 2 P and 2 D terms relative to the ground ( 4 S ) term are constrained by requiring that all six lines give the same radial velocity, consistent with independent limits placed on the motion of the O + gas and the planetary nebula data.