On the Structure and Physical Origin of the Weak Interaction Between H and CO

The adiabatic potential energy surface of the H-CO complex in the van der Waals region, described by Jacobi coordinates (r = 1.128 Å, R, Θ), was investigated using the supermolecular coupled-clusters CCSD(T) method. Our calculations indicate a minimum for bent arrangements. It was found on the carbon side of CO molecule at R = 3.6 Å (Θ = 76°) with a well depth of De = -156.5 μEh. The saddle points are localised at linear conformations for R = 4.37 Å (Θ = 0°) and R = 3.91 Å (Θ = 180°). The physical origin of the studied interaction was analysed by the intermolecular perturbation theory based on the single-determinant unrestricted Hartree-Fock wave function. The separation of the interaction energies shows that the locations of the predicted stable bent structure is primarily determined by delicate balance between the repulsive Heitler-London and attractive dispersion and induction energy components.