Role of Electron–Ion Dissociative Recombination in $$\hbox {CH}_{4}$$ Microwave Plasma on Basis of Simulations and Measurements of Electron Energy

Abstract

C–H bond activation was studied in low pressure microwave plasma discharges in methane. Electron energy loss channels were analyzed in view of promoting vibrational excitation. The molecular dissociative recombination (DR) channel is concluded to play multiple roles in the hydrocarbon plasma chemistry. DR increases the electron temperature with input power density and simultaneously breaks the hydrocarbon chains. Depending on the ionic species considered, plasma density $$\hbox {n}_e$$ in the range of $$10^{17}-10^{19}\,\hbox {m}^{-3}$$ ($$10^{-6}-10^{-4}$$ ionization degree) and the electron mean energy $$ $$ in the range of $$2-4\hbox { eV}$$ were estimated on basis of a Boltzman solver. $$ $$ from $$2-3\hbox { eV}$$ measured with Thomson scattering anchored the microwave discharges in a preferential regime for vibrational excitation. The best agreement with experiments was obtained when $$\hbox {C}^{+}$$ is the dominant ion in the $$\hbox {CH}_{4}$$ microwave plasma, formed through successive DR and charge exchange reactions from molecular ions.