GAS-PHASE CLUSTERING REACTIONS OF NO+ AND NO2+ WITH CH3NO2

The gas-phase clustering reactions of NO+ and NO2+ with CH3NO2 were st udied with a pulsed electron beam high-pressure mass spectrometer. The rmochemical quantities, Delta H(n-1,n)degrees and Delta S(n-1,n)degree s, of the clusters NO+(CH3NO2)(n) and NO2+(CH3NO2)(n) with n = 1-4, we re determined. The -Delta H(n-1,n)degrees values show a gradual decrea se with n, suggesting that the interaction involved in the clusters is mainly electrostatic. The measured bond enthalpy of NO+-CH3NO2, 25.2 +/- 0.9 kcal/mol, is slightly greater than that of NO2+-CH3NO2, 22.1 /- 0.9 kcal/mol. The thermochemical stabilities of both NO+(CH3NO2)(n) and NO2+(CH3NO2)(n) clusters with n = 2-4 are found to be about the s ame. This Letter supports the results of Cacace and co-workers derived from FT-ICR measurements. (C) 1998 Elsevier Science B.V. All rights r eserved.