Multipolar long-range electrostatic, dispersion, and induction energy terms for the interactions between two identical alkali atoms Li, Na, K, Rb, and Cs in various electronic states

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Abstract
For the alkali dimers Li2, Na2, K2, Rb2, and Cs2 long‐range potential energy curves of the molecular states corresponding to the asymptotes n s+n s and n s+n p have been investigated from standard perturbation method up to second order in the multipolar expansion approximation of the interaction energy. Two different cases have been considered: (i) neglecting spin‐orbit effects and then values of the long‐range expansion coefficients C n , n=(3), 6, 8, (10) have been determined (ii) including spin‐orbit effects and then potential energy curves have been determined numerically and are graphically displayed. Very good agreement is obtained between present curves and very recent long‐range experimental ones for the X 1Σ+ g state of Li2 and for the X 1Σ g + and 1Π g states of Na2. The position and the energy of purely long‐range extrema of the states 1 u (2 S 1/2+ 2 P 1/2), 1 u (2 S 1/2+2 P 3/2) and 0 g −(2 S 1/2+2 P 3/2) have been determined for each alkali dimer investigated.