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, $\alpha \mathrm{}\left(r\right)\mathrm{}$, to which the second dielectric virial coefficient $B_{\epsilon }$ is directly proportional, decreases with decreasing $r$, giving a theoretical value of $B_{\epsilon }=-0.093\mathrm{}$ a.u. at room temperature, compared with the experimental result $B_{\epsilon }=-0.06\mathrm{}\pm 0.04$ a.u., measured by Orcutt and Cole [J. Chem. Phys. 46, 697 (1967)]. This is the first calculation that predicts the correct sign of $B_{\epsilon }$. 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 $\alpha \mathrm{}\left(r\right)\mathrm{}$. Furthermore, the anisotropy of the pair polarizability $\beta \mathrm{}\left(r\right)\mathrm{}$ can be represented by a simple form: $\beta \mathrm{}\left(r\right)=6\mathrm{}{\alpha }^2{r}^{-3\mathrm{}}-\lambda e^{\frac{-r}{r_0}}$,, where $r_0=0.74\mathrm{}$ 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.