Electron-impact ionization of CClF₃ and CHClF₂: absolute cross sections and fragmentation dynamics

Area of Science:

• Chemical Physics
• Atomic and Molecular Collisions
• Atmospheric Chemistry

Background:

• Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are significant atmospheric pollutants.
• Understanding their electron-impact ionization is crucial for atmospheric modeling and predicting their environmental fate.

Purpose of the Study:

• To experimentally determine absolute total and partial ionization cross sections for CFC-13 and HCFC-22.
• To investigate the fragmentation patterns and identify major ionic species formed.
• To computationally explore the formation dynamics of metastable dications for HCFC-22.

Main Methods:

• Experimental measurement of electron collision ionization cross sections from 20 to 1000 eV.
• Mass spectrometry to identify ionic fragments.
• Adiabatic ionization and partial potential energy surface calculations for dication formation.

Main Results:

• For CFC-13, CF3+ and CClF2+ were the dominant fragments, indicating significant Cl and F atom release.
• For HCFC-22, fragmentation primarily yielded C(H)F2+, C(H)ClF+, and C(H)Cl+ ions.
• Metastable dications (CHClF22+ and CClF22+) were studied, with CHClF22+ forming via double-electron emission and CClF22+ observed from unstable CClF32+ dissociation.

Conclusions:

• Electron collisions with CFC-13 and HCFC-22 lead to extensive fragmentation, releasing halogen atoms.
• The study provides insights into the formation pathways and stability of dications, relevant to atmospheric chemistry.
• Experimental and computational data contribute to a better understanding of HCFC and CFC degradation processes.