Charged cores in ionized 4He clusters

Experimental and theoretical studies in large ionic helium clusters have suggested the presence of a diatomic (and occasionally triatomic) charged molecular core surrounded by the other atoms which are bound to it by weaker interactions. The understanding of the interactions between the system He2+ and an additional He atom of the cluster is therefore important in order to start modelling the full cluster interaction potential. In the present work we carry out a new set of calculations on the full potential and on the bound states supported by the He2+ isolated ion and further extend them to generate a Rigid Rotor (RR) potential energy surface (PES) for the triatomic system with He2+ kept at its equilibrium geometry (2.0 a.u.). The 13 bound states which were found and the overall angular anisotropy that exists for this potential energy surface (PES) are discussed in detail. We additionally show results of calculations on the surface vibrational extension to nine different values of the He2+ interatomic distance, thereby generating a fuller, three-dimensional interaction potential. A simpler modelling of the latter via ''Pseudo Rigid Rotor'' calculations for the bound states with a vibrationally excited core is also presented and discussed. (authors)