Observation of magic numbers within Ar_nH₂O⁺ heteroclusters

We present in this communication the observation of magic numbers for the heterocluster ion Ar_nH₂O⁺ for n = 3, 9, and 15 which we attribute to the stability of the cluster ion. On comparison with the calculations of Bohmer and Peyerimhoff for Ar_nXe⁺, we feel this data suggests that, in the case of Ar_nH₂O⁺, the water cation sits at the center of the argon cluster, representing the first example of an oxygen-containing molecule exhibiting such behavior. However, while Bohmer and Peyerimhoff predict a magic number for Ar₁₂Xe⁺, we do not observe one for Ar₁₂H₂O⁺. We postulate that this difference may be due to the water cation distorting the structure of the solvating argons.