Electron and positron scattering from 1,1-C2H2F2

Area of Science:

• Atomic and Molecular Physics
• Quantum Chemistry
• Chemical Physics

Background:

• 1,1-difluoroethylene (1,1-C2H2F2) is a molecule with limited prior experimental and theoretical study regarding its interaction with electrons and positrons.
• Understanding the scattering dynamics and resonance phenomena in small fluorinated hydrocarbons is crucial for various chemical and physical processes.

Purpose of the Study:

• To conduct the first comprehensive experimental and theoretical investigation of electron and positron scattering from 1,1-difluoroethylene (1,1-C2H2F2).
• To measure total cross sections (TCSs) and vibrational excitation cross sections.
• To assign observed resonance structures to specific symmetries and understand their origins.

Main Methods:

• Experimental measurements of electron and positron impact total cross sections (TCSs) from 0.4-1000 eV and 0.2-1000 eV, respectively, using a retarding potential time-of-flight apparatus.
• Crossed-beam method to measure vibrational excitation cross sections (1.3-49 eV) and electron impact elastic integral cross sections.
• Theoretical calculations using the Schwinger multichannel method with pseudopotentials in static-exchange and static-exchange plus polarization approximations.

Main Results:

• Resonance peaks in electron TCSs were observed around 2.3, 6.5, and 16 eV, primarily attributed to vibrational and elastic scattering channels with B2, B1, and A1 symmetries.
• A pi* resonance peak, shifted from ethylene (C2H4) to 2.3 eV in 1,1-C2H2F2, correlates with a decreasing C=C bond length.
• Positron impact revealed a significant peak below the positronium formation threshold (~1 eV) and less pronounced peaks around 5 and 20 eV.

Conclusions:

• The study provides the first detailed analysis of electron and positron scattering from 1,1-difluoroethylene, elucidating key resonance features.
• The observed resonance structures are linked to specific molecular vibrations and electronic symmetries, offering insights into the molecule's electronic structure.
• The findings contribute to a fundamental understanding of electron-molecule interactions in fluorinated hydrocarbons.