Electronic structure of Rydberg levels of the oxygen molecule

Rydberg-state wavefunctions which converge to the O + 2 ground state have been calculated at R=1.0, 1.117, 1.207, 1.3 and 1.4 AA for the total molecular symmetry of O + 2 (X 2 Pi g ) (nl) 1.3 Pi g.u for (nl) from (3, 0) to (10, 9) by a Hartree-Fock scheme with a frozen-core approximation. Comparison of the vertical excitation energy with the available experimental data shows a very good agreement for the lowest np sigma u 3 Pi u state, but a 10% discrepancy is found for the 3s sigma g 1.3 Pi g states. The ionisation energies are found to be insensitive to the O + 2 core wavefunctions. Variation of the ionisation energies with internuclear separation R is generally a few per cent or less from R=1.0 to 1.4 AA.