On the formation of water-containing negatively charged clusters from atmospheric pressure corona discharge in air

In this work we have studied the occurrence of negatively charged clusters in a corona discharge in atmospheric air at standard temperature and pressure. The discharge was operated in the point-to-plane configuration with a needle voltage of −1.2 kV and an electrode gap around 5 mm. The ions formed were accelerated and mass analyzed at an energy of 50 keV. The mass spectra are dominated by hydrated ions such as O2−(H2O)n and CO3−(H2O)n in contrast to our earlier studies at lower electrode voltages where mixed clusters such as NO3− (HNO3)m(H2O)n were dominant. In this study we only recorded masses corresponding up to 200 attached water molecules and found that for large n the peaks in the mass spectrum corresponding to O2−(H2O)n become dominating. We also demonstrate how collision induced dissociation (CID) coupled to charge reversal experiments –CR+ can provide lucid information about cluster composition.

Large anionic clusters with 200 water molecules are formed in a corona discharge of air using an STM needle held at −1 kV.Figure optionsDownload high-quality image (76 K)Download as PowerPoint slide