Helium aggregates doped with alkali dimer impurities: A finite temperature study of 4HeN-Rb2(3Σu+) complexes

A path integral Monte Carlo method has been used to study small (He-4)(N)-Rb-2((3)Sigma(+)(u)) complexes at low temperatures. We focus our investigation on the range 1 K <= T <= 2 K for aggregates of different sizes containing between 10 and 40 helium atoms. The extremely weak He-Rb-2 interaction, with a shallower potential depth and a longer equilibrium bond length than in the case of the He-He interaction, favors the preference of the alkali molecular dopant to reside on the helium droplet surface. In spite of the slight perturbation introduced by the rubidium dimer, it serves like a glue for the helium host that, at a given temperature, would not exist as a pure aggregate without the presence of the dopant molecule. It is found that the stability of the clusters increases with the number of He atoms surrounding the Rb-2 dimer. (C) 2012 Elsevier B.V. All rights reserved.