Cyclohexane Vibronic States: A Combined VUV Spectroscopy and Theoretical Study
Edvaldo Bandeira1, Alessandra S Barbosa1, Nykola C Jones2
1Departamento de Física, Universidade Federal do Paraná, Caixa Postal 19044, Curitiba 81531-980, PR, Brazil.
Molecules (Basel, Switzerland)
|April 26, 2025
Summary
This study details cyclohexane's vibronic features using VUV photoabsorption and TDDFT calculations. Cyclohexane's atmospheric fate is primarily governed by reactions with hydroxyl radicals, not photolysis.
Area of Science:
- Physical Chemistry
- Atmospheric Chemistry
- Quantum Chemistry
Background:
- Cyclohexane (C6H12) is a fundamental cyclic alkane with significant atmospheric relevance.
- Understanding its electronic excitations and atmospheric interactions is crucial for environmental modeling.
Purpose of the Study:
- To investigate the vibronic features of cyclohexane in the vacuum ultraviolet (VUV) region.
- To determine the primary atmospheric sink mechanism for cyclohexane.
- To elucidate the role of different vibrational modes in electronic transitions and molecular distortions.
Main Methods:
- High-resolution VUV photoabsorption spectroscopy.
- Quantum chemical calculations using time-dependent density functional theory (TDDFT).
- Density functional theory (DFT) for neutral and cationic ground-state molecular structure calculations.
Main Results:
- Major electronic excitations were assigned to mixed valence-Rydberg and Rydberg transitions.
- Fine structure in the photoabsorption spectrum was attributed to specific vibrational modes (CH2 scissoring, rocking, C-C stretching, CCC bending/CC torsion).
- Atmospheric photolysis lifetimes are negligible; reaction with hydroxyl (•OH) radicals is the main removal process.
Conclusions:
- The study provides a comprehensive understanding of cyclohexane's VUV vibronic structure.
- Cyclohexane's atmospheric persistence is limited by its reactivity with •OH radicals.
- Vibronic coupling involving CH2 scissoring and rocking modes is significant, while Jahn-Teller distortion effects are minor.
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