Emission of ionic water clusters from water ice films bombarded by energetic projectiles

Emission of water clusters M (H2O)n, where M denotes positive alkali metal ions, Liþ, Naþ, Csþ or negative halogen ions, Cl , Br , I from ice films frozen on metal substrates bombarded by energetic particles was studied by a molecular dynamics (MD) technique and by ToF-secondary ion mass spectrometry (SIMS) experiments. In the experiment, different concentrations of the salts NaCl, NaBr, and NaI were dissolved in water before freezing. The influence of ion charge and concentration on ion signal was investigated. Due to the different solvation structures of cations and anions in water, cationic clusters were demonstrated to eject more effectively than anionic clusters in both the simulations and experiments. The dependence of the absolute ion yield on the salt concentration is discussed in terms of ion pairing and clustering in the original solution and during emission. # 2004 Elsevier B.V. All rights reserved.