The frozen-core approximation for diatomic molecules: the lowest¹Σ⁺states of H₂

Adiabatic potential energies for the two lowest 1 Sigma + states of the hydrogen molecule have been calculated in the frozen core approximation over a range of internuclear separations from 0.2 to 4 au. The results are comparable with the SCF calculation of Coulson (1938) for the X1 Sigma g+ ground state, and with the multi-configuration calculation of Browne (1969) for the B1 Sigma u+ excited state. Transition moments for the X1 Sigma g+-B1 Sigma u+ electronic transition have also been computed.