Superexcited states of the hydrogen molecule converging to the first excited state of the hydrogen molecular ion

The Feshbach operator formalism was used to calculate thirty doubly excited states of the Hz molecule of the symmetries (1)Sigma(g,u)(+) (1)Pi(g,u), and (1)Delta(g,u) for internuclear distances up to 8 a.u. Basis functions involving Sonine polynomials and centered on either nucleus or on the center of nuclear mass allowed accurate inclusion of many one-electron molecular orbitals. Comparison is made with previous results in the literature.