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Ab initio intermolecular potential of Ar-C2H2 refined using high-resolution spectroscopic data
Clément Lauzin1, Laurent H Coudert, Michel Herman
1Service de Chimie quantique et Photophysique CP160/09, Faculté des Sciences, Université Libre de Bruxelles (ULB) , Av. Roosevelt, 50, B-1050 Bruxelles, Belgium.
High-resolution infrared spectra of the argon-acetylene (Ar-C2H2) complex revealed new subbands and refined intermolecular potential energy surfaces. Analysis of the ground vibrational state was satisfactory, but discrepancies arose for the excited stretching state.
Area of Science:
- Molecular Spectroscopy
- Intermolecular Forces
- Quantum Chemistry
Background:
- The argon-acetylene (Ar-C2H2) complex is a van der Waals system studied to understand intermolecular interactions.
- Previous spectroscopic studies have characterized some of its vibrational bands.
Purpose of the Study:
- To record and analyze the high-resolution infrared spectra of the ν1 + ν3 (2CH) band of the Ar-C2H2 complex.
- To refine the intermolecular potential energy surfaces (IPES) for the ground and excited vibrational states.
- To investigate discrepancies in the excited state analysis.
Main Methods:
- High-resolution infrared spectroscopy was employed to record spectra in the 6544–6566 cm⁻¹ range.
- Ab initio calculations were performed to determine the intermolecular potential energy surface.
- Spectroscopic data was used to optimize the IPES and assign new subbands.
Main Results:
- Observed and assigned previously unreported K(a) subbands (1←2, 2←3, 3←2) for the ν1 + ν3 band.
- Obtained refined intermolecular potential energy surfaces for the ground and excited vibrational states.
- Reproduced microwave transitions for the ground state with high accuracy (5 MHz RMS deviation).
- Observed systematic discrepancies in the analysis of the excited stretching state.
Conclusions:
- The study successfully expanded the spectral assignments for the Ar-C2H2 complex.
- Refined IPES were obtained, showing good agreement for the ground state but highlighting challenges for the excited state.
- Further theoretical and experimental investigations are needed to resolve discrepancies in the excited state.
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