Ab initio potential energy curves and vibrational levels for the c, l, and i states of the hydrogen molecule
Potential energy curves for the hydrogen molecule in the c3Π u, I1Π g, and i3Π g state have been calculated in the Born-Oppenheimer approximation. Highly flexible wavefunctions have been used, and for each state the calculations have been carried out for 40 different internuclear distances in the region 1 ≤ R ≤ 12 a.u. For the Π g states the wavefunctions are known to change their character around R = 5 a.u. The effect of this change on various components of the energy has been analyzed. The vibrational Schrödinger equation for all states has been solved for H 2, HD, and D 2. For H 2 the resulting energies are compared with the experimental values and it is shown that the adiabatic effects are likely to be responsible for the existing discrepancy between the theoretical and experimental values.