Ab initio study of energy, structure and dynamics of the water–carbon dioxide complex

The supermolecular Moller–Plesset perturbation theory (MPPT) is applied to calculate and analyze selected portions of the potential-energy surface (PES) of the H2O⋯CO2 complex. Two kinds of minima have been found. The global minimum, which corresponds to the T-shaped structure with the C atom bonded to the O atom, and the local minimum for the H-bonded arrangement OCO⋯HOH. The global minimum was estimated to be 920 cm−1 deep at the fourth order of MPPT combined with the extended spdf-quality basis set supplemented with bond functions. At the same level of theory the optimal H-bonded structure is 357 cm−1 higher in energy, and reveals a small 10° departure from the collinear arrangement OCO⋯H–O. Both the T-shaped and H-bonded forms are primarily bound by the electrostatic term, which is twice as large as the dispersion component. One-dimensional sections of the potential-energy surface were subsequently used to calculate vibrational energy levels for the wagging motion of the water moiety in the T-shaped and H-bonded forms. Two-dimensional cuts of the PES along the intermolecular Jacobi coordinates, r and θ, were employed to simulate the dynamics of the stretch–bend coupling close to the minima.