Intermolecular potential energy surface and second virial coefficients for the nonrigid water-CO dimer.

A seven-dimensional potential energy surface is calculated for the interaction of water and carbon monoxide using second-order Moller-Plesset theory, coupled-cluster theory, and extrapolated intermolecular perturbation theory. The effects of stretching the CO molecule and bending the water molecule are included. The minimum energy structure of the water-CO dimer changes from an H-C hydrogen bond to an H-O hydrogen bond when the CO bond length increases by less than 10 pm from its equilibrium value. Second virial coefficients for the water-CO interaction are calculated for a wide range of temperatures and compared with the limited experimental data. Allowing the CO bond length and water bond angle to vary has little effect on the second virial coefficients.