Gas-phase clustering reactions of NO+ and NO2+ with CH3NO2

The gas-phase clustering reactions of NO+ and NO2+ with CH3NO2 were studied with a pulsed electron beam high-pressure mass spectrometer. Thermochemical quantities, ΔHn−1, no and ΔSn−1, no, of the clusters NO+(CH3NO2)n and NO2+(CH3NO2)n with n=1–4, were determined. The −ΔHn−1, no values show a gradual decrease 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 same. This Letter supports the results of Cacace and co-workers derived from FT–ICR measurements.