CHARACTERIZATION OF GROUND-STATE WAVEFUNCTIONS BY MEASURED ELECTRONIC PROPERTIES .2. DIPOLE MOMENT AND FIELD GRADIENT OF NITROGEN TRIFLUORIDE

A particular localized-orbital type of LCAO MO wavefunction is used to calculate the dipole moment and field gradient at the nitrogen atom in NF 8. Because the wavefunction is not obtained by the usual self-consistent-field procedure, the results for the various observables depend on the choice of calculation parameters such as the polarity of the σ bonds, the amount of π bonding, and the hybridization of the lone-pair orbitals on the fluorine atoms. This dependence is studied in detail and it is concluded that with reasonable choices of input parameters, good agreement with experiment can be obtained. Thus, the localized orbitals specified by setting the σ-bond coefficient equal to 0.875, the π-bond coefficient equal to 0.0, and the fluorine lone-pair orbital angle equal to 112.7°, yield a dipole moment of 0.236 D and a total field gradient at the N atom of -2.007 a.u. The experimental dipole moment is 0.234±0.004 D and the experimental field gradient is -l.505 to -3.010 a.u. depending on the exact value of the nuclear quadrupole moment of nitrogen.