Ab initio potential energy surface, infrared spectrum, and second virial coefficient of the He–CO complex

Abstract

Symmetry‐adapted perturbation theory has been applied to compute the intermolecular potential energy surface of the He–CO complex. The interaction energy is found to be dominated by the first‐order exchange contribution and the dispersion energy. The ab initio potential has a single minimum of ε_m=−24.895 cm⁻¹ for the linear CO–He geometry at R_m=6.85 bohr. The computed potential energy surface has been analytically fitted and used in converged variational calculations to generate bound rovibrational states of the He–CO molecule and the infrared spectrum, which corresponds to the simultaneous excitation of vibration and internal rotation in the CO subunit within the complex. The predicted positions and intensities of lines in the infrared spectrum are in good agreement with the experimental spectrum [C.E. Chuaqui et al., J. Chem. Phys. 101, 39 (1994)]. The theoretical potential was also checked by comparison of computed excess second virial coefficients with the experimental data. The ab initio interaction virial coefficients, including quantum corrections, lie within the experimental error bars over a wide range of temperatures.