Ab initio potential energy surface and infrared spectra of H2-CO and D2-CO van der Waals complexes

A new four-dimensional intermolecular potential energy surface for the H2-CO complex with fixed intramolecular distances of H2 and CO is presented. The symmetry-adapted perturbation theory has been used to calculate the interaction energy. A large basis set of spdfg type has been used including bond functions. An analytical fit of the ab initio potential energy surface has the global minimum of −109.272 cm−1 at the intermolecular separation of 7.76 bohr for the linear geometry with the C atom pointing toward the H2 molecule. This potential has been used to calculate rovibrational energy levels of CO-para-H2 and CO-ortho-D2 complexes. The resulting dissociation energies are 23.709 cm−1 and 30.756 cm−1, respectively. The computed levels have been used to generate the infrared spectrum accompanying the fundamental vibrational excitation of CO. The transition energies predicted agree well with those observed by McKellar [Chem. Phys. Lett. 186, 58 (1991)].