POTENTIAL-ENERGY CURVES FOR THE (3)SIGMA(G)(+) AND (3)SIGMA(U)(+) STATES OF H-2

The Born-Oppenheimer (BO) potential energy curves for several of the lowest 3SIGMA(g)+ and 3SIGMA(u)+ states of H-2 at internuclear distances R less-than-or-equal-to 5 au are calculated using large elliptical orbitals 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 3SIGMA(u)+ states and the second up through fifth excited 3SIGMA(g)+ states are given. It is concluded that for the triplet Rydberg states of H-2 the CI method is as effective at describing electron correlation as are the methods that include the interelectron distance explicitly.