Jahn-Teller effect in van der Waals complexes; Ar-C6H6 + and Ar-C6D6 +

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Spectroscopy

Background:

• Argon interacting with benzene cation forms a van der Waals complex with degenerate electronic states.
• Understanding these interactions is crucial for molecular spectroscopy and quantum chemistry.
• Jahn-Teller effects significantly influence the potential energy surfaces and spectral properties.

Purpose of the Study:

• To calculate the potential energy surfaces for argon interacting with the benzene cation.
• To investigate the nonadiabatic (Jahn-Teller) coupling effects on these surfaces.
• To compute vibronic states and predict far-infrared spectra for Ar-C(6)H(6)(+) and Ar-C(6)D(6)(+).

Main Methods:

• Ab initio calculations of interaction energies and ionization potentials.
• Outer valence Green's function method for electronic structure.
• CAS-SCF(5,6) method for nonadiabatic coupling matrix elements.
• Two-state diabatic model with harmonic oscillator basis functions for vibronic states.

Main Results:

• Identified coinciding minima on the two potential surfaces at a specific geometry.
• Calculated binding energies for both neutral and ionic complexes, showing good agreement with experimental data for the deuterated complex.
• Predicted strong absorption lines in the far-infrared spectrum, correlating well with experimental measurements.
• Observed a large splitting in the van der Waals bend mode due to quadratic Jahn-Teller activity.

Conclusions:

• The calculated potential energy surfaces and vibronic states accurately describe the Ar-benzene(+) complex.
• The study confirms the significant role of Jahn-Teller coupling in shaping the complex's properties.
• Theoretical predictions of spectral lines provide valuable insights for experimental validation and further research.