On the formation and fragmentation of nitrate in mixed clusters using atmospheric pressure corona discharge in air

We report on studies of NO3− in mixed clusters of HNO3 and H2O, NO3−(HNO3)m(H2O)n with m = 0–3 and n = 0–300. The ions were formed in a corona discharge in ambient air in the point to plane configuration and investigated in a sector type mass spectrometer. The yields of individual ions depend strongly on the shape of the needle and the needle voltage. An STM needle with a tip radius of around 20 nm, resulted in clusters with m = 2 and 3 and n around 100. After collision-induced dissociation (CID) at 50 keV with Ne gas both positive and negative fragment ions were recorded and unambiguous information about the cluster composition was obtained. Density functional theory (DFT) calculations have been employed to shed light on the experimental findings.