New CO-CO interaction potential tested by rovibrational calculations

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Spectroscopy

Background:

• Accurate potential energy surfaces (PES) are crucial for understanding molecular interactions and predicting spectroscopic properties.
• The carbon monoxide (CO) dimer is a fundamental system for studying intermolecular forces.
• Previous calculations using high-level coupled cluster methods provided a benchmark, but computational cost is high.

Purpose of the Study:

• To develop a reliable and computationally efficient four-dimensional potential energy surface (PES) for the rigid CO dimer.
• To investigate the accuracy of a combined density functional theory-symmetry adapted perturbation theory (DFT-SAPT) approach for describing the CO dimer interaction.
• To refine the PES by incorporating experimental data for improved agreement with observed rovibrational spectra.

Main Methods:

• Calculation of a four-dimensional PES for the CO dimer using a hybrid DFT-SAPT scheme.
• Fitting the calculated PES to analytic functions for efficient use in dynamical calculations.
• Computation of rovibrational energy levels using the fitted PES and comparison with experimental data.

Main Results:

• The DFT-SAPT PES demonstrates quality comparable to a previously computed coupled cluster single double and perturbative triples [CCSD(T)] surface.
• A weighted average of the DFT-SAPT and CCSD(T) potentials yields excellent agreement with experimental data for both ((12)CO)(2) and ((13)CO)(2) isotopologues.
• The optimal weighting was determined by matching the calculated energy gap between the lowest rotational stacks to experimental values.

Conclusions:

• The combined DFT-SAPT and CCSD(T) approach provides a highly accurate and potentially more accessible method for generating PES for molecular dimers.
• The refined PES accurately reproduces experimental rovibrational spectra, validating its quality for spectroscopic predictions.
• This work offers a valuable computational tool for further studies of the CO dimer and related systems.