A generalised 17-state vibronic-coupling Hamiltonian model for ethylene

Area of Science:

• Computational Chemistry
• Theoretical Chemistry
• Quantum Chemistry

Background:

• Previous work established 17 dominant configurations for ethylene's electronic structure.
• A strategy was developed for a 17-quasidiabatic-state Hamiltonian using dynamical symmetry.

Purpose of the Study:

• To develop a generalized vibronic-coupling Hamiltonian model for ethylene.
• To incorporate dynamic electron correlation for improved Rydberg state energetics.
• To validate the quasidiabatic states by comparing with experimental spectra.

Main Methods:

• Fitted potential energy surfaces using a generalized vibronic-coupling Hamiltonian model.
• Inclusion of dynamic electron correlation via multireference configuration interaction.
• Quantum dynamics calculations for the absorption spectrum.

Main Results:

• A two-dimensional model for CC bond stretching and torsion was developed.
• Improved energetics for Rydberg states were achieved.
• The calculated absorption spectrum shows good agreement with experimental data.

Conclusions:

• The chosen quasidiabatic states are validated by the model's accuracy.
• The 2D model provides a good approximation of ethylene's experimental absorption spectrum.
• This approach offers a robust framework for studying vibronic couplings in molecules.