Asymptotic theory for the (2)Sigma(u) Van der Waals potentials of alkali dimer cations

The (2)Sigma(u) state Van der Waals potentials of alkali dimer cations Li-2(+), Na-2(+), K-2(+), Rb-2(+) and Cs-2(+) are calculated from the asymptotic exchange and polarization energies. The potentials of all these systems are generated by the same analytical formula with parameters depending only on the properties of the atomic constituents. The results agree with accurate CI calculations. The dipole-dipole-quadrupole hyperpolarizability for these systems is large and it is necessary to include this third-order term in the polarization energy for an accurate determination of the potential. However, the overlap correction and the damping of the induction series, although conceptually important, have only a minor effect. (C) 1998