OBSERVATION OF MAGIC NUMBERS WITHIN NO NH3 MIXED CLUSTER IONS/

The metastable decomposition of photoionized NO/NH3 clusters has been investigated employing a reflectron time-of-flight mass spectrometer. The metastable dissociation spectra of the most prominent cluster ion species NO+(NH3)(n) (3 less than or equal to n less than or equal to 2 8) show that the rate coefficient for the loss of one NH3 molecule fro m the cluster rapidly increases up to n = 13 and thereafter is nearly independent of the cluster size. This is interpreted as evidence of a stable structure that consists of a central NO+ ion surrounded by a fi rst solvation shell of 12 NH3 molecules.