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

摘要

Using a reaction field model, we have derived symmetryhyphen;adapted expressions for the van der Waals dipoles of atomndash;heteroatom and atomhyphen;Dinfin;hmolecule pairs, with nonoverlapping charge distributions.The leading van der Waals contributions vary asRminus;7in the intermolecular separationRand depend upon products of the polarizability agr;agr;bgr;(iohgr;) of one molecule with a dipolendash;quadrupole hyperpolarizabilityBagr;bgr;,ggr;dgr;(0,iohgr;) of the other, integrated over imaginary frequencies. We have developed new approximations for these integrals in terms of the static polarizabilities agr;agr;bgr;, the hyperpolarizabilitiesBagr;bgr;,ggr;dgr;, and the van der Waals energy coefficientsC6andC8(both isotropic and anisotropic components for atomndash;molecule pairs). The approximations agree well with accurate perturbation results for two model systems. Applied to Hesdot;sdot;sdot;H2, our approximations give the first direct results for the leading van der Waals contributions to the dipole. In two symmetry components of the Hesdot;sdot;sdot;H2dipole at long range, van der Waals effects are larger than induction effects; both should be included in fitting collisionhyphen;induced rotohyphen;translational spectra.