Rydberg levels of the oxygen molecule associated with excited states of the ion core

Rydberg states (Σg^-, Σᵤ^-, Πg, and Πᵤ) of O₂ that converge to the B²{{Σ}}g^{{{-}}}$, ${b}⁴Σg^-, and c⁴{{Σ}}ᵤ^{{{-}}}$ excited states of the parent ${O}₂⁺$ ion have been calculated. The Rydberg electron wave functions are expanded by one-center basis functions that are solutions of an electron moving in a sphericalized potential of the parent-ion core. The Rydberg energy levels are obtained by diagonalizing the full Hamiltonian which includes both the spherical and nonspherical parts of the potential. Rapid convergence of the expansion is assured because the basis functions are already a good approximation to the Rydberg-state wave functions. The calculations cover (nl) from (3,0) to (10,7) and m=0 and 1 using two internuclear distances, R=1.2 A{} and the equilibrium distances of the parent excited O₂⁺ states. The results are compared with photoabsorption and electron-impact energy-loss experiments. Good agreement is seen for the nsσg, npσᵤ, and npπᵤ series but the ndσg states exhibit larger discrepancies.