Electron-impact ionization of CCl₄ and CCl₂F₂

B. G. Lindsay, K. F. McDonald, W. S. Yu, R. F. Stebbings, and F. B. Yousif.

J. Chem. Phys. 121, 1350-1356 (2004)

Absolute partial and total cross sections for electron-impact ionization of CCl₄ and CCl₂F₂ are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ion species are collected with equal efficiency irrespective of their initial kinetic energies. Data are presented for production of CCl₃⁺, CCl₂⁺, CCl⁺, C⁺, Cl₂⁺, and CCl₃²⁺ from CCl₄; and for production of CCl₂F⁺, CClF₂⁺, CClF⁺, (CCl⁺ + CF₂⁺), Cl⁺, CF⁺, F⁺, and C⁺ from CCl₂F₂. Data are also reported for formation of (CCl₂⁺, Cl⁺) and (CCl⁺, Cl⁺) ion pairs from CCl₄. The total cross section for each target is obtained as the sum of the partial cross sections. The overall uncertainty in the absolute cross sections for most of the singly-charged ions is ±5-7%. The present partial cross sections for lighter fragment ions are found to be considerably greater than had been previously reported but the most recent total cross section measurements agree well with those reported here. Neither the binary-encounter-Bethe theory nor the Deutsch-Märk theory reproduces the experimental cross sections correctly for both targets.