The delocalization of SF₆ in helium clusters

Variational calculations of the ground state structure and the excitation spectrum of ⁴He clusters doped with an SF₆ molecule show that, for clusters size larger than approximately 100 atoms, a spherically symmetric configuration with the impurity molecule at the center of the cluster is unstable. The instability is indicated by the 'softening' of the droplet's collective dipole excitation. This instability strongly suggests that the SF₆ molecule is delocalized inside larger helium droplets and may be found near a non-isotropic environment such as the surface.