Unexpected stability of [Cu center dot Ar](2+), [Ag center dot Ar](2+), [Au center dot Ar](2+), and their larger clusters

Experimental observations following the ionization of neutral group 11 meta l/argon complexes have revealed the presence of doubly charged ions of the form [M . Ar-n](2+) for n in the range 1-6. Of particular interest are two features of the results. First, the unexpected stability of the dimer ions, [M . Ar](2+), since similar species involving a molecule rather than a rar e gas atom are often unstable with respect to charge transfer. Ab initio ca lculations show the dimers owe their stability to a combination of a strong electrostatic interaction and the high ionization energy of argon. A secon d feature to the results is the high relative intensities of the [M . Ar-4] (2+) and [M . Ar-6](2+) ions. Calculations show these complexes to consist of square-planar D-4h structures, with the additional two atoms in [M . Ar- 6](2+) occupying axial sites, which are Jahn-Teller distorted. The calculat ed relative binding energies support the preferential stability of these tw o structures. (C) 2001 American Institute of Physics.