H 2 : The Critical Juncture between Polymerization and Dissociation of Hydrocarbons in a Low‐temperature Plasma

The chemistry in an argon plasma jet, admixed with a small percentage of CH 4 , C 2 H 2 , H 2 and mixtures thereof, is investigated by means of residual gas a4lysis. Polymerization of such hydrocarbon precursors is known to occur when their densities exceed the Ar + ion density. This paper shows that polymerization also occurs for precursor gas flows far below the initial Ar + ion flow emanating from the plasma source. This is entirely due to the negative effect of H 2 on the Ar + ion density. Adding 1–2% of H 2 to the total argon and hydrocarbon gas flow suffices to initiate polymerization. Although, H 2 can be injected directly into the system, fragmentation of the hydrocarbon precursors themselves can likewise supply (part of) the required H 2 . Polymerization is furthermore enhanced when both precursors are used together. The contribution of C 3 H y species to the plasma chemistry will likewise be substantiated.