Electronic structure of the benzene dimer cation

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Quantum Chemistry

Background:

• Understanding the electronic structure and stability of molecular ions is crucial in chemistry.
• Benzene dimer cations are fundamental systems for studying non-covalent interactions and charge transfer.
• Previous studies have explored benzene dimer properties, but detailed electronic state characterization of its cation remains an active area.

Purpose of the Study:

• To computationally investigate the electronic states and geometries of the benzene dimer cation.
• To characterize the bonding patterns and spectral features of different benzene dimer cation isomers.
• To compare theoretical predictions with experimental spectroscopic data for validation.

Main Methods:

• Employed the equation-of-motion coupled-cluster model with single and double substitutions (EOM-CCSD) for ionized systems.
• Calculated relaxed ground state geometries for various isomers, including t-shaped, sandwich, and displaced sandwich configurations.
• Utilized a qualitative dimer molecular orbital framework for spectral analysis.

Main Results:

• Identified ten lowest electronic states for the benzene dimer cation across different configurations.
• Determined the lowest energy structure to be a displaced sandwich with a binding energy of 20 kcal/mol.
• Observed good agreement between calculated electronic spectra and experimental gas phase and liquid phase data, including charge resonance bands.

Conclusions:

• The displaced sandwich structure represents the most stable configuration for the benzene dimer cation.
• The study provides a detailed electronic state catalog and explains spectral features using molecular orbital theory.
• Reassignment of local excitation peaks in experimental spectra is suggested based on observed electronic state ordering.