Zero-Point Vibrational Corrections to One-Electron Properties of the Water Molecule in the Near-Hartree—Fock Limit

Abstract

The zero‐point vibrational motion of the water molecule in its ground electronic state is analyzed with a near‐Hartree—Fock potential energy surface constructed from a (9s5p2d/4s1p) /[4s3p2d/2s1p] basis set of contracted Gaussian orbitals. The harmonic and cubic force constants relative to the computed minimum are obtained, and a normal coordinate analysis is carried out for several isotopic variants. A set of one‐electron properties including molecular moments, field gradients, forces, and densities is computed at each point on the potential surface, and then averaged over the zero‐point motion with a vibrational wavefunction which contains anharmonicity terms through the cubic constants. The vibrational corrections are typically about 1% of the equilibrium values, but are as large as 20% in cases such as the ¹⁷O quadrupole coupling constant along the C₂ axis. The theoretical isotope shifts for the quadrupole moments of H₂O and D₂O are in good agreement with experiment. Predictions are made for isotope shifts in other properties. A b initio values of the bond and angle displacement coordinates and their root‐meansquare amplitudes are also determined.