THE STRUCTURE OF AR3+

Extended basis set CI calculations were performed to contribute to the discussion concerning the equilibrium ground state nuclear configurat ion of the Ar3+ cluster. A relativistic pseudopotential was used to de scribe the Ar core and only the valence electrons were treated explici tly in the calculation. The quality of the basis set used and the leve l of correlation reached were justified by the calculation of the spec troscopic constants of Ar2+ where direct experimental verification was possible. Spin-orbit interaction was taken into account when the theo retical and experimental dissociation energies D(e) of the Ar2+ molecu le were compared. The experimental value with 'spin-orbit interaction removed' D(e) = 1.39 +/- 0.02 eV matched well with our calculated D(e) = 1.385 eV. The Ar3+ molecule was found to be linear and symmetric wi th an unexpectedly short bond length r=4.73 a0.