Term structure of Mg I calculated in a frozen-cores approximation

A two-electron model, similar to that which has been previously used to calculate energy levels for Be I, is applied to the bound states and resonance structure of Mg I. The method is based on electron scattering techniques and is equivalent to a frozen-cores approach. The two-electron Hamiltonian contains a core polarisation potential which includes a term that accounts for the valence-valence interaction by the distorted inner core; it is shown that this term is essential in order to obtain consistent results. The convergence of the close-coupling expansion is examined and the model is found to provide an accurate overall representation for the Mg + +e - system. Calculated bound states and resonant states are presented for the 1 S, 3 S, 1 P 0 , 3 P 0 , 1 D, 3 D, 3 P, 1 D 0 , 3 D 0 spectral series of Mg I.