Vibrational Dynamics of the H2O . HF Complex. Potential Energy and Electric Dipole Moment Surfaces

A total of 330 points on the potential energy and electric dipole moment surfaces of the ground electronic state of the H2O . HF complex have been calculated ab initio using the SCF method and many-body perturbation theory (MBPT). To keep the calculations manageable, the geometry parameters of H2O were fixed at their experimental values and only certain two dimensional sections of the total surfaces have been evaluated. for each of the two-dimensional surface section, analytic potential energy and electric dipole moment functions have been fitted through the points and corresponding vibrational energy levels and effective electric dipole moments have been calculated using approximate vibrational Hamiltonians. The calculated values of resulting vibrational energies and effective electric dipoles from differently wide intervals for different vibrational modes. The intervals corresponding to the most interesting low frequency modes (out-of-plane and H2O vs HF stretching) are very narrow and coincide satisfactory with the corresponding experimental values. A very reasonable agreement has also been obtained for the equilibrium geometry, electric dipole moment and dissociation energy De of the complex. These findings lead us to believe that the calculated potential energy and electric dipole moment surfaces are sufficiently accurate for predicting purposes and rationalization of the so far unassigned spectral data of H2O . HF.