(12)C2H2-Ar van der Waals complex.

Area of Science:

• Physical Chemistry
• Molecular Spectroscopy
• Computational Chemistry

Background:

• Van der Waals complexes are crucial for understanding intermolecular forces.
• Acetylene-argon (C2H2-Ar) serves as a model system for studying weak interactions.
• Previous studies provide a foundation for further theoretical and experimental investigations.

Purpose of the Study:

• To present new theoretical and experimental findings on the acetylene-Ar van der Waals complex.
• To review existing literature on the C2H2-Ar system.
• To investigate the influence of complexation on acetylene's structure and vibrational properties.

Main Methods:

• Ab initio calculations at the MP2 level with large basis sets and diffuse functions.
• Accounting for basis set superposition error (BSSE) in calculations.
• Experimental production of C2H2-Ar in a supersonic expansion at 9 K rotational temperature.
• High-resolution spectroscopy using continuous-wave cavity ring-down spectroscopy (CW-CRDS).

Main Results:

• Complexation minimally alters acetylene's structure and slightly lowers vibrational frequencies.
• Calculated properties (structure, spectrum, dissociation energy) show low sensitivity to imposed acetylene structure.
• Experimental recording and assignment of sub-bands (K(a) = 0, 1, 2) of the nu(1) + nu(3) band.
• Determination of upper-state rotational constants and a mean lifetime of approximately 7.5 ns from line profile analysis.
• Observation of K-doubling anomalies and local perturbations in the spectrum.

Conclusions:

• Acetylene-Ar complexation has a limited impact on the internal structure and vibrational modes of acetylene.
• Experimental spectroscopic data provide insights into the complex's dynamics and intermolecular interactions.
• Observed spectral perturbations and K-doubling suggest complex interactions within the acetylene-Ar system.