Production of large O-containing neutral hydrocarbon species by aCH4-O2microwave discharge

The product of O-containing species in ${\mathrm{CH}}_4$-${\mathrm{O}}_2$ plasmas has been studied as a function of the oxygen partial pressure in a microwave flow tube with 2.465 GHz, 6 W, and 2.2 torr total pressure. Mass spectrometry, coupled with ${\mathrm{Li}}^{+}$-ion attachment techniques, was used for the identification of the products. Studies have clearly shown the presence of various O-containing stable polymer molecules, ${\mathrm{C}}_{\mathit{n}}$ ${\mathrm{H}}_{2\mathit{n}+2\mathrm{}}$O, ${\mathrm{C}}_{\mathit{n}}$ ${\mathrm{H}}_{2\mathit{n}}$O, and ${\mathrm{C}}_{\mathit{n}}$ ${\mathrm{H}}_{2\mathit{n}}$ ${\mathrm{O}}_2$ (n goes up to 9). The relative concentration profiles of these products have been determined as a function of ${\mathrm{O}}_2$ composition in the feed gas. An assumption was presented that alcohols, aldehydes, and possibly O-containing radical species form in the ${\mathrm{CH}}_4$-${\mathrm{O}}_2$ plasma. A reaction scheme is speculated which may account for these observed profiles.