The dielectric response to an inhomogeneous electric field has been investigated for Ba and ${\text{Ba}}_2$ within a molecular beam experiment. The ratio of the polarizabilities per atom of ${\text{Ba}}_2$ and Ba is determined to be $1.30\pm 0.13$. The experimental result is compared to a high level ab initio quantum chemical coupled cluster calculation with an energy-consistent scalar relativistic small-core pseudopotential for Ba. For the barium atom a polarizability of $40.82{\text{Å}}^3$ is obtained and the isotropic value of the polarizability calculated for ${\text{Ba}}_2$ is $97.88{\text{Å}}^3$, which is in good agreement with the experimental results, demonstrating that a quantitative understanding of the interaction between two closed-shell heavy element metal atoms has been achieved.

• Received 17 August 2007

DOI:https://doi.org/10.1103/PhysRevA.76.052515