Ions studies by argon tagging include the hydrated proton H + ( H 2 O ) n Ar with n = 2 to 5, hydrated 18-crown-6 ether alkali metal ions, hydrated alkali metal ions, transition metal acetylene complexes, protonated ethylene,
2.
Some hydration structures are quite large : the magic ion number structure ( called " magic " because of its increased stability with respect to hydration structures involving a comparable number of water molecules this is a similar usage of the word " magic " as in ab initio method molecular dynamics simulations have shown that, on average, the hydrated proton resides on the surface of the cluster.