Anisotropy of long range interactions between linear molecules: H2-H2 and H2-He

Abstract

We derive a closed expression for the orientation dependence of the long range interaction coefficients of Σ state linear molecules and then calculate the dispersion and induction multipole interaction coefficients for the systems H₂-H₂ and H₂-He up to R ^-10 terms inclusive. The monomer states are described by SCF-LCAO wave functions with polarization functions optimized with respect to the different multipole polarizabilities. The anisotropy factors γ₈ and γ₁₀, describing the orientation dependence of the R ^-8 and R ^-10 terms, are approximately equal and much larger than γ₆, due to the occurrence of the (completely anisotropic) mixed-pole terms.