A DIM model for homogeneous noble gas ionic clusters

The method of diatomics-in-molecules (DIM) is applied to the calculation of the energy of the homogeneous noble-gas ionic clusters Ar _n ⁺ and Xe _n ⁺ forn=3, 4, ..., 22. The trimers are stable symmetric linear molecules exhibiting chemical binding, a result in agreement both with ab initio calculations and with previous DIM work. The clusters up ton=13 are best described as a trimer ion surrounded by neutrals, whereby the charge distribution changes slightly with increasingn. Both noble gases exhibit a special stability associated with the completion of the first shell of neutral atoms atn=13. Asn increases from 13 to 22, there is a greater delocalization of the positive charge, the central ion tending to become a linear tetramer, symmetric for Xe and unsymmetric for Ar. Energies of the excited electronic states are reported and the possibility of developing simpler DIM models for the clusters and for mixed noble gases is discussed.