3-BODY DISPERSION COEFFICIENTS FOR ALKALI-METAL ATOMS

We study the nonadditive part of the long-range interaction among thre e alkali-metal atoms in their ground states. Using nondegenerate pertu rbation theory, up to the third order, we have computed the dispersion coefficients C for three alkali-metal atoms interacting via their ele ctric dipole moments. Both heteronuclear and homonuclear cases are con sidered. The numerical values for the C coefficients suggest that such three-body dipole interaction effects may not be neglected in the des cription of the long-range surface potential interaction for alkali-me tal atoms. Furthermore, we show that approximate formulas for C of Mid zuno and Kihara [J. Phys. Soc. Jpn. 11, 1045 (1956)] give results in e xcellent agreement with results of our calculations. Comparisons are g iven of our results with results of others and with results of other a pproximate formulas. The effect on our results for the C coefficient o f uncertainties in the experimental values of the static dipole polari zabilities, on which our results depend, is also analyzed.