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

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The electron energy dependence of partial cross sections for dissociation of methane into CH3 and CH2 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 (N2→N+N, N+N+) using threshold-ionization mass spectrometry. The other was the measurement of sticking coefficients of CH3, CH2, 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 m2 at 24 eV for CH3 radical and 0.72×10-20 m2 at 18 eV for CH2 radical.