Distribution of species within an ethylene electron cyclotron resonance-microwave plasma

Abstract

Electron cyclotron resonance microwave plasmas consisting of 2% ethylene in hydrogen and 2% ethylene in deuterium have been probed using the pulsed supersonic, plasma sampling technique. Comparison of the compositions of these two chemically equivalent plasmas provides the basis for examining the details of species interconversion and overall hydrocarbon chemistry within these plasmas. The ethylene/hydrogen plasma is shown to be composed of 9% ethane radical (C2H5), 38% ethylene (C2H4), 8% ethylene radical (C2H3), and 41% acetylene (C2H2), with the remaining counts attributed to impurities in the plasma. Due to interferences between the daughter ions of the radical species and the parent ions of ethylene and acetylene, the concentrations of radical species, reported above, represent only a lower limit estimate, based only on the parent ion intensity. Analysis of the mass spectrum obtained for the analogous deuterium plasma, based on the results from the hydrogen plasma experiments, reveal the acetylene components of the deuterium plasma to be 14% undeuterated (C2H2), 43% singly deuterated (C2HD), and 43% doubly deuterated (C2D2). The extensive deuteration of the acetylene indicates that the majority of the chemistry in these plasmas is repeated cycles of hydrogen (deuterium) atom addition to acetylene followed by abstractions from the radical species (C2HxD3−x). The absence of any significant intensity due to doubly, triply, or fully deuterated ethylenes indicates that the addition of hydrogen (deuterium) to the radical species C2HxD3−x is a much more rare event than abstraction.