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

Abstract

For the alkali dimers Li2, Na2, K2, Rb2, and Cs2 long-range potential energy curves of the molecular states corresponding to the asymptotes ns+ns and ns+np 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 Cn, 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 1Σg+ and 1Πg states of Na2. The position and the energy of purely long-range extrema of the states 1u(2S1/2+ 2P1/2), 1u(2S1/2+2P3/2) and 0g−(2S1/2+2P3/2) have been determined for each alkali dimer investigated.