Electron impact ionization of the NF 3 molecule

Abstract

We report measurements of the absolute cross sections for the electron-impact ionizaton of the NF 3 molecule from threshold to 200 eV. Absolute values and shapes for the NF 3 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 NF 3 ionization cross section is 0.35 ± 0.06 Å 2. The dissociative ionization of NF 3 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 Å 2 (NF + 2) and 0.7 ± 0.15 Å 2 (NF + at 70 eV. Two channels contribute to the observed NF + ion signal, the single positive ion formation NF 3 → NF + + 2F and the positive ion pair formation NF 3 → 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 Å 2 for F + (at 70 eV) which can be attributed primarily to the double positive ion formations NF 3 → NF + + F + + F. The upper limit for the N + cross section from NF 3 is 0.1 Å 2 at 70 eV.