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 Angstrom, R, Theta), 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 Angstrom (Theta=76degrees) with a well depth of D-e=-156.5 muE(h). The saddle points are localised at linear conformations for R=4.37 Angstrom (Theta=0degrees) and R=3.91 Angstrom (Theta=180degrees). 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.