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).