A mass spectrometric study of ions extracted from a point-to-plane dc corona discharge in N2O at atmospheric pressure

Abstract

In this paper we report the first study of ions formed in both positive and negative point-to-plane corona discharges fed by N2O containing less than 0.1% of H2O at atmospheric pressure. Considerable differences were observed in the mass spectra of the ions produced from corona discharges of different polarities. In all the discharges the product ions were observed mainly in the form of clusters. However, in positive corona discharges only four major groups of cluster ions were monitored whereas in all corona discharges operated with negative polarity a much more varied and complex variety of negative ions was observed. The spectrum of positive ions is highly sensitive to the content of water vapour in nitrous oxide with H3 O+ · (H2O)n clusters (especially H3O+ · (H2O)3) and NO+ · (H2O)n clusters being the dominant products. The yield of NO+ · (H2O)n was found to increase strongly with increasing discharge current while the yield of H3O+ · (H2O)n clusters was reduced. Spectra of ions detected in negative corona discharges contain clusters of NO−, , ions and also clustered with N2O, NO, NO2, H2O and HNO3. This paper reports how the yield of such ions is influenced by the plasma characteristics and discusses how these results may be explained by physical and chemical processes in the plasma.