Prediction and observation of a new, ground state, dipole-bound dimer anion: The mixed water/ammonia system

The first study of very low energy electron attachment to mixed water-ammonia clusters is reported here. A ‘‘magic’’ cluster anion distribution with strong similarities to that of pure water cluster anions is observed. The mixed (${\mathrm{H}}_2$O . . .${\mathrm{NH}}_3$ ${)}^{\mathrm{-}}$ dimer is created under very specific experimental conditions and its existence is a test of the theory of electron binding by a dipole. This fragile species has a very small electron binding energy as inferred from field detachment experiments.