Search

Abstract

The major ionic and neutral product species in CH4/H2 plasmas were studied as a function of the hydrogen composition in a 2.465-GHz microwave flow tube at 30-W power and 2.2-Torr total pressure. Mass spectrometry, coupled with Li⁺ ion attachment techniques, was used for identification of the products. Various neutral and ionic polymer molecules with carbon numbers of up to 12 were identified, and the relative concentration profiles of these species were determined as a function of H2 composition in the feed gas. A possible reaction scheme to account for these observed profiles is suggested. From a comparison of the ionic species with the neutral species in this plasma, it is apparent that dissociative electron ionization is a likely process in the ion chemistry of the CH4/H2 plasma. In addition, a general interpretation of the results was attempted for polymeric neutral product formation, particularly with regard to the role of hydrogen atom abstraction processes and radical processes.

The neutral and ionic products in CH4/N2 plasmas were studied as a function of the nitrogen partial pressure in a microwave (MW) flow tube with 2.465 MHz, 30 W, and 0.6 Torr total pressure. Mass spectrometry, coupled with Li⁺ ion attachment techniques, was used to identify the products. Our study clearly showed the presence of various polymer compounds of hydrocarbons, nitriles, amines, and possibly hydrazines, as well as their ionized species. Possible reaction schemes, which may account for the observed profiles, are considered for some of these products, particularly with regard to the role of radical and ionic condensation reaction processes. An attempt was made to link both the ionic and neutral species to a proposed mechanism. It is apparent from a comparison with the neutral species in this plasma that the proton transfer reaction plays a significant role in the ion chemistry of the CH4/N2 plasma.