Absolute cross sections for the dissociative electron impact ionization of the CFx (x = 1-3) free radicals

V. Tarnovsky, P. Kurunczi, D. Rogozhnikov, K. Becker

Research output: Contribution to journalArticlepeer-review

Abstract

We studied the dissociative ionization of the CFx (x = 1-3) free radicals by electron impact and measured absolute partial cross sections and appearance energies for the formation of the various fragment ions. Fast beams (3-3.5 kV) of CF3, CF2 and CF were prepared by near-resonant charge transfer of CF+3, CF+2 and CF+ with Xe under conditions where the neutral beams contained primarily ground state ions with little vibrational excitation (0.5 eV or less). Absolute cross sections for the various molecular fragment ions were measured from threshold to 200 eV with peak cross sections of up to 1.3 Å2. The cross sections for the formation of the atomic C+ and F+ ions were found to be small (0.3 Å2 or less) except for the F+ cross section from CF2. The measured appearance energies indicate that the fragment ions are formed with excess kinetic energies ranging from essentially zero to about 3 eV per fragment. The CF+ cross section from CF2 shows a second onset which corresponds to the double positive ion formation CF2 → CF+ + F+. Extensive ion trajectory calculations were carried out in order to quantify the collection efficiency of our apparatus for fragment ions formed with excess kinetic energy.

Original languageEnglish (US)
Pages (from-to)181-194
Number of pages14
JournalInternational Journal of Mass Spectrometry and Ion Processes
Volume128
Issue number3
DOIs
StatePublished - Oct 9 1993

Keywords

  • Electron collision cross sections
  • Electron impact ionization
  • Free radicals
  • Plasma processing

ASJC Scopus subject areas

  • Spectroscopy

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