Triple‐Dipole Interaction. I. Theory

Third‐order perturbation theory is applied to the van der waals‐type interaction between neutral atoms. An interaction between triplets of atoms results. The derivation of the third‐order energy interaction W0′′′, is outlined, the procedure being somewhat similar to that used by London in his application of second‐order perturbation theory to interatomic interaction. Since the perturbing potential is limited to the dipole‐dipole term, the energy W0′′′ is called the triple‐dipole interaction. The latter depends not only on the interatomic distances but also on the shape of the triangle formed by the three atoms; W0′′′ is positive for all acute and negative for most obtuse triangles.