Polarizability of Interacting Atoms: Relation to Collision-Induced Light Scattering and Dielectric Models

Abstract

The polarizability tensor of a pair of interacting He atoms has been calculated as a function of internuclear separation $r$ using the fully self-consistent Hartree-Fock theory. It was found that the trace of the polarizability tensor, $\ensuremath{\alpha}(r)$, to which the second dielectric virial coefficient ${B}_{\ensuremath{\epsilon}}$ is directly proportional, decreases with decreasing $r$, giving a theoretical value of ${B}_{\ensuremath{\epsilon}}=\ensuremath{-}0.093$ a.u. at room temperature, compared with the experimental result ${B}_{\ensuremath{\epsilon}}=\ensuremath{-}0.06\ifmmode\pm\else\textpm\fi{}0.04$ a.u., measured by Orcutt and Cole [J. Chem. Phys. 46, 697 (1967)]. This is the first calculation that predicts the correct sign of ${B}_{\ensuremath{\epsilon}}$. We conclude that for He the effects of overlap are of opposite sign from and of sufficient magnitude to overcome the contributions of the van der Waals interaction to $\ensuremath{\alpha}(r)$. Furthermore, the anisotropy of the pair polarizability $\ensuremath{\beta}(r)$ can be represented by a simple form: $\ensuremath{\beta}(r)=6{\ensuremath{\alpha}}^{2}{r}^{\ensuremath{-}3}\ensuremath{-}\ensuremath{\lambda}{e}^{\frac{\ensuremath{-}r}{{r}_{0}}}$,, where ${r}_{0}=0.74$ a.u., and the collision-induced light-scattering spectrum predicted by this form has an essentially exponential line shape. These results are in qualitative agreement with recent work on collision-induced light-scattering spectra from rare gases.