Electron‐impact ionization cross sections of the SiF₃ free radical

Absolute cross sections for electron‐impact ionization of the SiF₃ free radical from threshold to 200 eV are presented for formation of the parent SiF⁺₃ ion and the fragment SiF⁺₂, SiF⁺, and Si⁺ ions. A 3 keV beam of SiF₃ is prepared by near‐resonant charge transfer of SiF⁺₃ with 1,3,5‐trimethylbenzene. The beam contains only ground electronic state neutral radicals, but with as much as 1.5 eV of vibrational energy. The absolute cross section for formation of the parent ion at 70 eV is 0.67±0.09 Ų. At 70 eV the formation of SiF⁺₂ is the major process, having a cross section 2.51±0.02 times larger than that of the parent ion, while the SiF⁺ fragment has a cross section 1.47±0.08 times larger than the parent. Threshold measurements show that ion pair dissociation processes make a significant contribution to the formation of positively charged fragment ions.