Perturbation calculations of the van der Waals potentials of He(2 3S, 2 1S) metastable atoms with rare gas atoms

Perturbative expressions are presented for calculating the adiabatic potential curves between metastable He(2 3S, 2 1S) helium atoms and the rare gas atoms Ne, Ar, Kr and Xe. The first-order terms are obtained by assuming that the main contribution comes from the 2s-wave electron of the metastable helium atom and the s-wave electrons in the outermost shell of the rare gas atom. With the second-order van der Waals terms modified with Tang–Toennies damping functions, a simple analytical expression is obtained for the entire potential curves. The van der Waals well depths and positions are in good agreement with the experiments.