Neutral and ion kinetics in glow discharges of H2 / O2 mixtures. Diagnostics and modelling

London, United Kingdom, 14–17 April 2014; http://plasma14.iopconfs.org/homeLow pressure plasmas in electrical discharges with H2 and O2 are of interest in a variety of fields. In astrochemistry, the formation of H2O and H3O+ is of great relevance as they can be detected in interstellar environments. In fusion research, discharge cleaning is used to eliminate the residual molecules in a vacuum vessel, of which oxygen and water are major components. In this work, we present a study of the chemistry of neutral and ionic species in H2/O2 plasmas based on the experimental diagnostics and kinetic modelling of hollow cathode discharges at different pressures and mixture proportions. Neutral and ion distributions are measured by mass spectrometry, and Langmuir probes provide charge densities and electron temperatures. As expected, apart from the precursors, H2O is detected in considerable amounts. Concerning the charged species, pure hydrogen and oxygen ions are detected together with mixed ones. With increasing pressure, the ion distributions are dominated by H3O+ for mixtures with H2 concentrations higher than ~ 30%, in contrast, the protonated species O2H+ is hardly formed. A zero order kinetic model is used to explain the experimental results. H2O is produced via plasma-surface interactions in a multistep process. The ion distributions are determined in each case by a balance between the relative weights of electron impact processes and proton transfer chemistry. The relevance of negative ions in the plasma chemistry is also studied.Peer Reviewe