Observation of ‘‘magic numbers’’ in the population distributions of the (NH3)<i>n</i>−1NH+2 and (NH3)<i>n</i>H+2 cluster ions: Implications for cluster ion structures

Abstract

We have measured the relative yields of the cluster ions (NH3)n−1NH+2 and (NH3)nH+2 produced by electron impact ionization of a supersonic molecular beam of neutral ammonia clusters, as functions of cluster ion size, neutral beam stagnation temperature, and electron impact energy. Our observation of a magic number at n=7 in the distribution of (NH3)n−1NH+2 cluster ions is interpreted in terms of an intracluster bimolecular association reaction between a nascent NH+2 daughter ion and an adjacent NH3 solvent molecule, giving rise to a protonated hydrazine product ion. Our observation of magic numbers at n=5 and n=8 in the (NH3)nH+2 cluster ion distribution is consistent with the production of the N2H+8 Rydberg radical cation via an intracluster ion–molecule reaction. Our experimental results are consistent with recent theoretical predictions concerning the structure and stability of N2H+8 ions.