Electron-Impact Dissociation of Methane into CH₃ and CH₂ Radicals II. Absolute Cross Sections

Abstract

The electron energy dependence of partial cross sections for dissociation of methane into CH 3 and CH 2 radicals has been reported in part I of this paper. In order to assign absolute values to these relative cross sections, two additional experiments were carried out. One was cross-section measurement for electron-impact nitrogen dissociation (N 2 →N+N, N+N + ) using threshold-ionization mass spectrometry. The other was the measurement of sticking coefficients of CH 3 , CH 2 , and atomic nitrogen. According to these measurements, the absolute partial cross sections for neutral dissociation were determined: maximum cross section is 1.4×10 -20 m 2 at 24 eV for CH 3 radical and 0.72×10 -20 m 2 at 18 eV for CH 2 radical.