Electron-impact ionization of CCl4 and CCl2F2

Area of Science:

• Atomic and Molecular Physics
• Chemical Physics
• Plasma Science

Background:

• Electron-impact ionization is crucial for understanding plasma chemistry and material processing.
• Previous cross-section data for CCl4 and CCl2F2 were limited or inconsistent.
• Accurate cross-section data are essential for modeling and simulating complex chemical systems.

Purpose of the Study:

• To experimentally determine absolute partial and total cross sections for electron-impact ionization of CCl4 and CCl2F2.
• To identify and quantify all major fragment ions produced from these molecules.
• To compare experimental results with theoretical predictions from established models.

Main Methods:

• Utilized a time-of-flight mass spectrometer coupled with a position-sensitive detector.
• Measured electron-impact ionization cross sections over an energy range from threshold to 1000 eV.
• Ensured equal collection efficiency for all product ion species, regardless of their kinetic energy.

Main Results:

• Reported cross sections for numerous fragment ions, including CCl3+, CCl2+, CCl+, C+, Cl2+, CCl3(2+) from CCl4, and CCl2F+, CClF2+, CClF+, (CCl+ + CF2+), Cl+, CF+, F+, C+ from CCl2F2.
• Presented data on ion pair formation, such as (CCl2+, Cl+) and (CCl+, Cl+) from CCl4.
• Observed significantly larger partial cross sections for lighter fragment ions compared to previous reports, while total cross sections showed good agreement with recent measurements.

Conclusions:

• Experimental cross sections for electron-impact ionization of CCl4 and CCl2F2 were accurately determined.
• Existing theoretical models (Binary-Encounter-Bethe and Deutsch-Mark) did not adequately reproduce the experimental findings for both molecules.
• The comprehensive dataset provides valuable benchmarks for theoretical calculations and plasma modeling.