Potential-Energy Curves for the X (1)Sigma(+)(g), b(3)Sigma(+)(u), and C (1)Pi(u) States of the Hydrogen Molecule

Previous calculation of the ground-state energy of H(2) has been extended to include large internuclear distances and accurate potential-energy curve for 0.4 <= R <= 10.0 a.u. is presented. For 0.4 <= R <= 4.0 a.u. expectation values of several operators have also been calculated. The calculation was made using a wavefunction in the form of an expansion in elliptic coordinates. The wavefunction depends on the interelectronic distance but, in contrast to the James-Coolidge expansion, is flexible enough to describe properly the dissociation of the molecule. Extensive calculations have also been made for the repulsive (3)E(u)(+) state (1.0 <= R <= 10.0) and for the (1)Pi(u) state (1.0 <= R <= 10.0). In the former case a van der Waals minimum has beenfound at R=7.85 a.u. and 4.3 cm(-1) below the dissociation limit. For the (1)Pi(u) state the computed binding energy D(e)=20 490.0 cm(-1) and the equilibrium internuclear distance R(e)=1.0330 angstrom are in a satisfactory agreement with the experimental values D(e)=20 488.5 cm(-1) and R(e)=1.0327 angstrom. In this case a van der Waals potential maximum has been found to occur at R=9.0 a.u. and 105.5 cm(-1) above the dissociation limit. Preliminary results for the (1)Sigma(+)(u) state at R approximate to R(e) are also given.