Cluster ions:: Gas-phase stabilities of NO+(CH3CN)n and NO2+(CH3CN)n with n=1-5

The gas-phase equilibria of the clustering reactions of NO+ and NO2+ with CH3CN were measured with a pulsed electron-beam high-pressure mass spectrometer. Thermodynamic quantities. DeltaH degrees (n-1,n) and DeltaS degrees (n-1,n), of the NO+(CH3CN)(n), and NO2+(CH3CN)(n) clusters with n=1-5 were determined. It was found that both clusters with n=3 are relatively more stable toward dissociation. For n=1-4, the thermochemical stabilities of NO+(CH3CN)(n) were observed to be slightly higher than those of corresponding NO2+(CH3CN)(n). The results suggest a switch of the attacking site on the core ion for the fifth ligand molecule of these clusters at n=4-->5. (C) 2000 Elsevier Science B.V.