Long-range behavior of the transition dipole moments of heteronuclear dimers XY (X, Y = Li, Na, K, Rb) based on ab initio calculations

Abstract

The ab initio electronic transition dipole moments (ETDMs) of heteronuclear dimers XY (X, Y = Li, Na, K, Rb) were calculated between the ground and excited states converging to the lowest three dissociation limits. The spin-allowed ETDMs were evaluated in a wide range of interatomic distances, R, by means of the quasi-relativistic electronic wave functions obtained by the multi-reference configuration interaction method. The inner-shell electrons (2 electrons for Li and Na atoms, and 10 and 28 for K and Rb, respectively) were described using the non-empirical shape-consistent effective core potentials. The l-independent core polarization potentials of each atom were used to take core-polarization and core-valence correlation effects into account. The long-range behavior of both singlet–singlet X¹Σ⁺–(2,3)¹Σ⁺;(1,2)¹Π and triplet–triplet a³Σ⁺–(2,3)³Σ⁺;(1,2)³Π transition moments is perfectly fitted at large R-distance by the asymptotic formula of X. Chu and A. Dalgarno, Phys. Rev. A: At., Mol., Opt. Phys., 2002, 66, 024701: , where the coefficient β is equal to 2 and −1 for the Σ–Σ and Σ–Π transitions, respectively. The n²S–n²P transition moments, d^A, and dynamic polarizabilites, α^B, of the alkali atoms in the n²S state extracted from the present molecular calculations coincide with their empirical and ab initio counterparts to within a few percent.