Appearance energies of small cluster ions and their fragments

Abstract

Appearance energies of the cluster ions (CO₂)⁺_n(2 ⩽n⩽ 4), (N_2′O)⁺_n(2 ⩽n⩽ 4) and (NH₃)_nNH⁺₄(0 ⩽n⩽ 7), and the cluster ion fragments (N₂O · O)⁺ and (N₂O · NO)⁺ have been determined by electron impact ionization of neutral clusters formed in a supersonic molecular beam. Results obtained for (CO₂)⁺_n(2 ⩽n⩽ 4), (N₂O)⁺_n(2 ⩽n⩽ 4), (N₂O · NO)⁺ and (NH₃)_nNH⁺₄(O ⩽n⩽ 2) are in general agreement with previously reported appearance energies for these species, while the appearance energies of (N₂O · O)⁺ and (NH₃)_nNH⁺₄(3 ⩽n⩽ 7) have been measured for the first time. Binding energies deduced from appearance energy measurements for the (CO₂)⁺₂, (CO₂)⁺₃ and (N₂O)⁺₂ cluster ions are observed to be in accord with results obtained using ion–molecule equilibrium methods. Possible mechanisms for the formation of the cluster fragment ions (N₂O · O)⁺ and (N₂O · NO)⁺ are discussed.