Ethenedithione (S=C=C=S): Does It Obey Hund's Rule?

Area of Science:

• Quantum Chemistry
• Theoretical Chemistry
• Molecular Spectroscopy

Background:

• Hund's rule is a fundamental principle in atomic and molecular spectroscopy.
• Previous studies proposed ethenedithione as a potential exception to Hund's rule.
• Understanding the electronic states of small molecules is crucial for theoretical chemistry.

Purpose of the Study:

• To investigate the electronic states of ethenedithione (S=C=C=S).
• To determine the energetic relationship between the singlet excited state (1Δg) and the triplet ground state (3Σg-) of ethenedithione.
• To verify or refute the proposed violation of Hund's rule in ethenedithione's equilibrium structure.

Main Methods:

• High-level ab initio calculations were employed.
• Computational methods were used to determine molecular energies and electronic configurations.
• The study focused on the singlet (1Δg) and triplet (3Σg-) states of ethenedithione.

Main Results:

• The singlet excited state (1Δg) of ethenedithione is calculated to be significantly higher in energy (24 kJ mol⁻¹) than its triplet ground state (3Σg-).
• The calculated energy difference is in agreement with the predictions of Hund's rule.
• The results indicate that ethenedithione does not violate Hund's rule in its equilibrium structure.

Conclusions:

• Ethenedithione does not serve as an example for the violation of Hund's rule.
• The electronic structure of ethenedithione is consistent with established quantum mechanical principles.
• High-level computational chemistry accurately predicts the energetic ordering of electronic states.