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Why the CC Stretch in HCC Is So Anharmonic.
1Quantum Theory Project, Department of Chemistry, The University of Florida, Gainesville, Florida 32611, United States.
The Journal of Physical Chemistry. A
|September 9, 2021
Summary
The ethynyl radical
Area of Science:
- Quantum Chemistry
- Molecular Spectroscopy
- Theoretical Chemistry
Background:
- The ethynyl radical (C2H) exhibits significant anharmonicity in its CC stretching mode.
- This anharmonicity is notably larger than in related molecules with triple bonds.
Purpose of the Study:
- To investigate the cause of the marked anharmonicity in the CC stretching mode of the ethynyl radical.
- To elucidate the role of vibronic coupling in this phenomenon.
Main Methods:
- Vibronic coupling model analysis.
- Coupled-cluster (CC) theory calculations, including equation-of-motion CC (EOM-CC).
Main Results:
- The anharmonicity is attributed to vibronic interaction between the X̃²Σ⁺ and Ã²Π electronic states of CCH.
- A combination of strong coupling, modest energy gap, and CC stretch tuning significantly influences the anharmonic force field.
Conclusions:
- Vibronic interactions profoundly impact the anharmonicity of the CC stretching mode in ethynyl radical.
- EOM-CC methods offer advantages for calculating the force field of such systems.
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