Tunable diode laser diagnostic studies of H-2-Ar-O-2 microwave plasmas containing methane or methanol

Tunable infrared diode laser absorption spectroscopy has been used to detec t the methyl radical and ten stable molecules in H-2-Ar-O-2 microwave plasm as containing up to 7.2% of methane or methanol, under both flowing and sta tic conditions. The degree of dissociation of the hydrocarbons varied betwe en 30 and 90% and the methyl radical concentration was found to be in the r ange 10(10)-10(12) molecules cm(-3) The methyl radical concentration and th e concentrations of the stable C-2 hydrocarbons C2H2, C2H4, and C2H6, produ ced in the plasma decayed exponentially when increasing amounts of O-2 were added at fixed methane or methanol partial pressures. In addition to detec ting the hydrocarbon species, the major products CO, CO2, and H2O were also monitored. For the first time, formaldehyde, formic acid, and methane were detected in methanol microwave plasmas, formaldehyde was detected in metha ne microwave plasmas. Chemical modeling with 57 reactions was used to succe ssfully predict the concentrations in methane plasmas in the absence of oxy gen and the trends for the major chemical product species as oxygen was add ed.