Long-range dispersion coefficients for the low-lying electronic states of Mg-2 from the calculation of the frequency-dependent dipole polarizabilities of Mg in its ground and excited states

The frequency-dependent dipole polarizabilities are calculated for the five lowest states 3(1)S; 4(1)S; 3(1)P; 3(3)P and 4(3)S of Mg by using our time -dependent gauge invariant method (TDGI). Estimations of the long-range dis persion coefficients for all the first-molecular states dissociations of Mg -2 are proposed. Accuracy of the results is checked through the calculation s obtained from a length, a velocity and a mixed approach in the formulatio n of the oscillator strengths and the corresponding dynamic dipole polariza bilities. In all cases, the length results appear as a reference for the co mparison with some previous works concerning the ground state. The long-ran ge coefficients reported for almost all the low-lying states are new and pr edict a repulsive interaction between the 4(1)S states. (C) 2001 Elsevier S cience B.V. All rights reserved.