Theoretical Study of Valence Shell Excitation by Electron Impact in CCl₄

Area of Science:

• Theoretical Chemistry
• Quantum Mechanics
• Spectroscopy

Background:

• Valence shell excitation in carbon tetrachloride (CCl4) is crucial for understanding its photochemical behavior.
• Previous studies have not fully accounted for the impact of nuclear dynamics on electron excitation cross-sections.

Purpose of the Study:

• To theoretically investigate valence shell excitation in CCl4 using high-energy electron impact.
• To elucidate the influence of molecular vibration on electron excitation cross-sections and spectral features.

Main Methods:

• Calculated generalized oscillator strengths at the equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) level.
• Incorporated molecular vibration effects to account for nuclear dynamics.
• Compared theoretical results with recent experimental data for spectral feature reassignment.

Main Results:

• Identified dominant roles for excitations from Cl 3p nonbonding to σ* antibonding orbitals (7a1 and 8t2) below ~9 eV.
• Demonstrated that asymmetric stretching vibration significantly affects valence excitations at small momentum transfers.
• Found that vibrational effects considerably influence Cl formation in CCl4 photolysis.

Conclusions:

• Molecular vibrations play a substantial role in the electron excitation dynamics of CCl4.
• The study provides insights into spectral assignments and the mechanisms of Cl atom formation.