Mass Spectra of Negatively Charged Water and Ammonia Clusters

Slow electrons are mixed into a heavily clustered supersonic expansion of water and ammonia. The resulting negatively charged cluster ions are mass analyzed. Mass spectra for (H 2 O) n − , (D 2 O) n − , and (NH 3 ) n − are presented. The smallest cluster ions observed contain 11, 12, and 36 water, heavy water and ammonia molecules per clusters, respectively.