Electron impact ionization of the NF₃ molecule

We report measurements of the absolute cross sections for the electron-impact ionizaton of the NF₃ molecule from threshold to 200 eV. Absolute values and shapes for the NF₃ parent ionization cross section were obtained independently in two different laboratories using two different experimental techniques. The agreement was better than ±8%. At 70 eV, the absolute parent NF₃ ionization cross section is 0.35 ± 0.06 Ų. The dissociative ionization of NF₃ was studied primarily using the fast-beam technique. Absolute cross sections for the formation of the fragment ions NF⁺₂ and NF⁺ were found to be 1.05 ± 0.20 Ų (NF⁺₂) and 0.7 ± 0.15 Ų (NF⁺ at 70 eV. Two channels contribute to the observed NF⁺ ion signal, the single positive ion formation NF₃ → NF⁺ + 2F and the positive ion pair formation NF₃ → NF⁺ + F⁺ + F with an appearance energy of 36.5 ± 1.0 eV. While the NF⁺₂ fragment ions are formed with little excess kinetic energy for impact energies near threshold, the NF⁺ fragment ions are formed with a broad distribution of excess kinetic energies ranging from essentially zero to about 4 eV. Cross sections for the formation of the atomic fragment ions F⁺ and N⁺ were found to be small with a maximum value of 0.3 Ų for F⁺ (at 70 eV) which can be attributed primarily to the double positive ion formations NF₃ → NF⁺ + F⁺ + F. The upper limit for the N⁺ cross section from NF₃ is 0.1 Ų at 70 eV.