Ab initio potential energy curves for the lower states of the Mg-He system

Abstract
Ab initio CI calculations are presented for the 11 Sigma , 21 Sigma , 13 Sigma , 23 Sigma , 11 Pi and 13 Pi states of MgHe for energies up to 10 eV. All the states are purely repulsive. The lowest 3 Sigma and 1 Pi states cross at around 3 au and remain nearly degenerate down to 2 au. In the region from 3.2 to 2 au the 13 Sigma state is being progressively Rydbergised to the 4pz level and this change is reflected in the dipole moment function which changes sign. The matrix element of the spin-orbit operator is calculated in the region of the crossing and is reduced from the decoupled Mg atomic value due to the partial Rydbergisation of the 3p electron.