Polarizabilities of Ba and Ba2:: Comparison of molecular beam experiments with relativistic quantum chemistry

The dielectric response to an inhomogeneous electric field has been investigated for Ba and Ba-2 within a molecular beam experiment. The ratio of the polarizabilities per atom of Ba-2 and Ba is determined to be 1.30 +/- 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 A(3) is obtained and the isotropic value of the polarizability calculated for Ba-2 is 97.88 A(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.