Diagnosis of a CH4/N2 microwave discharge:: Ionic and neutral species

The neutral and ionic products in CH4/N-2 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/N-2 plasma.