Production and mass spectroscopic characterization of ammonium halide clusters

The ammonium halide clusters from solid crystals of NH4X (X = F, Cl, I) have been investigated by using a laser vaporization method and time of flight mass spectrometry. Positive ion clusters of NH4+(NH3)n(HF)m (n≤5, m≤5) and NH4+(NH3)n(HI)m (n≤10, m≤5) are detected with remarkable size effects. However, essentially no NH4+(NH3)n(HCl)m and negative ammonium halide clusters are observed. These results are interpreted within the framework of intra-cluster interactions and transitions from a hydrogen bonded complex to an ionic crystal of the ammonium halide clusters.