Excited states dipole polarizabilities of calcium atom and long-range dispersion coefficients for the low-lying electronic states of Ca2 and CaMg

The frequency-dependent dipole polarizabilities are calculated for the five lowest states 41S, 51S, 41P, 43P and 53S of Ca by using a time-dependent gauge invariant method. The difference of the polarizability (α(3P)−α(1S)) of 112.9 a.u., between the excited 3P state and the 41S ground state calculated from the TDGI method is in good agreement with the two experimental measurements of 96.5±16.4 and 90.4±13.8 a.u. obtained from the Stark frequency and phase shifts, respectively, by Morinaga et al. [Phys. Rev. A 54 (1996) 21]. As a consequence of our previous work referring to the Mg atom, the length formulation of the oscillator strengths has been used. Estimations of the long-range dispersion coefficients for the first molecular state dissociations of Ca2 and CaMg are proposed. Most of the results are new, and predict a repulsive behaviour for the 1Πg,u and 3Σ+g,u states of the 41S–41P and 51S–41P interactions, respectively.