Cross sections for radicals from electron impact on methane and fluoroalkanes

Molecular and atomic radicals from electron-impact dissociation of methane and a variety of fluoroalkanes are detected mass spectometrically as organotellurides produced by the reaction of the radicals at the surface of a tellurium mirror. The radicals detected include CH3 from CH4; CF3 from CF4 and CHF3; CHF2 from CHF3 and CH2F2; CH2F from CH3F; and CF3 and C2F5 from C2F6 and C3F8 produced by electron impact at energies between 10 eV and 500 eV. Relative cross sections are measured. These are placed on an absolute scale by comparison with related measurements. For the collision energies relevant to processing plasmas, 10–30 eV, it is shown that dissociation into neutrals rather than dissociative ionization is mainly responsible for the production of molecular radicals.