Shape Resonances and Elastic Cross Sections in Electron Scattering by CF₃Br and CF₃I

Area of Science:

• Plasma Physics and Chemistry
• Atomic and Molecular Physics
• Computational Chemistry

Background:

• Trifluoroiodomethane (CF3I) is a promising gas for plasma technologies, offering advantages over trifluorobromomethane (CF3Br).
• Understanding electron collision cross sections is crucial for modeling plasma transport and reactivity, especially for electron-induced molecular decomposition.
• Previous studies on CF3I and CF3Br electron collisions reported conflicting results regarding shape resonances and total cross sections.

Purpose of the Study:

• To resolve discrepancies in electron scattering data for CF3I and CF3Br.
• To perform ab initio calculations to determine accurate collision cross sections and resonance assignments.
• To investigate the impact of the heavy halogen atom on electron scattering properties.

Main Methods:

• Ab initio electron scattering calculations were performed for CF3I and CF3Br.
• Integral cross sections were computed and compared with experimental measurements.
• Analysis of shape resonances, including their character (σ*CX and σ*CF) and energy positions.

Main Results:

• Calculated integral cross sections show good agreement with recent experimental data, contrasting with earlier reports.
• A σ*CX resonance was identified at ~0 eV for CF3I and 1 eV for CF3Br.
• Three σ*CF shape resonances were found: a degenerate pair around 6 eV and a single resonance at 9.5 eV.

Conclusions:

• The study provides reliable electron collision cross section data for CF3I and CF3Br, resolving prior conflicts.
• The identified resonances offer insights into electron-driven dissociation pathways, particularly the role of the degenerate resonance in dissociative electron attachment.
• The findings highlight the significant influence of the heavy halogen atom on electron scattering dynamics and resonance characteristics.