Knowledge Bank

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 (9s 5p 2d/4s 1p)/[4s 3p 2d/2s 1p] 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 value, but are as large as 20% in some cases. Of particular interest are the dipole moment, 1.998 (equil), 2.002($H2O$), 2.001($D2O$, HDO) Debyes; $\mathrm{<mrow\; data-mjx-texclass="ORD">17</mrow>}O$ quadrupole coupling constant along the $C2$-axis, 0.79(equil), 0.95($H217O$) and 0.93 ($HD17O$) MHz; largest principal component of the quadrupole coupling constant at the deuteron, 370.6(equil), 367.1 ($D2O$), and 366.1 (HDO) KHz. Ab initio values of the bond and angle displacement coordinates and , and root-mean square amplitudes and are also determined; for $H2O$,they are 0.014\AA, 0.22$\mathrm{<mrow\; data-mjx-texclass="ORD">\circ </mrow>}$, 0.065\AA, and 9.04$\mathrm{<mrow\; data-mjx-texclass="ORD">\circ </mrow>}$, respectively.