Potential energy curves for the 3Σg+ and 3Σu+ states of H2

The Born-Oppenheimer (BO) potential energy curves for several of the lowest 3Σg+ and 3Σu+ of H2 at internuclear distances R ≤ 5 au are calculated using large elliptical orbital sets and full configuration interaction (CI) expansions. The resulting energies are shown to be surprisingly accurate compared with those obtained by using explicitly correlated basis functions of the generalized James-Coolidge or Hylleraas type. Accurate BO potential energy curves for the first three excited 3Σu+ states and the second up through fifth excited 3Σg+ states are given. It is concluded that for the triplet Rydberg states of H2 the CI method is as effective at describing electron correlation as are the methods that include the interelectron distance explicitly. (author)