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 C H3CN were measured with a pulsed electron-beam high-pressure mass spectrome ter. 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 de termined. It was found that both clusters with n=3 are relatively more stab le toward dissociation. For n=1-4, the thermochemical stabilities of NO+(CH 3CN)(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 E lsevier Science B.V.