Dipoles induced by van der Waals interactions during collisions of atoms with heteroatoms or with centrosymmetric linear molecules

Abstract

Using a reaction field model, we have derived symmetry-adapted expressions for the van der Waals dipoles of atom–heteroatom and atom-D∞h molecule pairs, with nonoverlapping charge distributions.The leading van der Waals contributions vary as R−7 in the intermolecular separation R and depend upon products of the polarizability ααβ(iω) of one molecule with a dipole–quadrupole hyperpolarizability Bαβ,γδ (0,iω) of the other, integrated over imaginary frequencies. We have developed new approximations for these integrals in terms of the static polarizabilities ααβ, the hyperpolarizabilities Bαβ,γδ, and the van der Waals energy coefficients C6 and C8 (both isotropic and anisotropic components for atom–molecule pairs). The approximations agree well with accurate perturbation results for two model systems. Applied to He⋅⋅⋅H2, our approximations give the first direct results for the leading van der Waals contributions to the dipole. In two symmetry components of the He⋅⋅⋅H2 dipole at long range, van der Waals effects are larger than induction effects; both should be included in fitting collision-induced roto-translational spectra.