Electron-impact dissociation of the methane molecule into neutral fragments

Abstract

The three most important electron-impact processes dissociating ${\mathrm{CH}}_{4}$ molecule into neutral fragments are $e+{\mathrm{CH}}_{4}\ensuremath{\rightarrow}{\mathrm{CH}}_{3}+\ensuremath{\cdots}$, $e+{\mathrm{CH}}_{4}\ensuremath{\rightarrow}{\mathrm{CH}}_{2}+\ensuremath{\cdots}$, and $e+{\mathrm{CH}}_{4}\ensuremath{\rightarrow}\mathrm{CH}+\ensuremath{\cdots}$. Neither experimental nor theoretical cross sections for the processes in a broad range of energy are available, except for the first process for which reliable measured cross sections for energies up to $500\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ are available. Only two measured values (at a single impact energy) of the cross section for the second process are available, and only two measured values (also at a single energy) of the cross section for the third process are available in the literature. Therefore, we derive in this work analytical dissociation cross sections for the second and the third processes mentioned above in the energy range up to $500\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. At higher (but still nonrelativistic) energies, we calculate the parameters of the Bethe-Born cross section for the second and the third processes.