Energies and widths of the lowest 1Σ+g states of H2

Positions and widths for the lowest 1Σ+g doubly excited autoionizing states of H2 at several internuclear separations have been obtained by the calculation of Siegert eigenvalues. This approach involves the direct computation of the complex resonance energy in a basis set of both real and complex Slater orbitals. When the complex orbitals are centered between the two atoms, the numerical results are in fair agreement with previous theoretical treatments, although the present width does not rise quite as much for larger internuclear separations. In addition, the sensitivity of the present results on the basis set is studied and improvements to the basis set which should provide converged positions and widths for these resonances are discussed