Nuclear Quadrupole Coupling in the NH3 Molecule

The electric field gradient q at the position of the nitrogen nucleus in the NH3 molecule is evaluated by using four representative molecular orbitals expressed as linear combinations of atomic orbitals. The integrals over atomic orbitals are carried out by the method of Barnett and Coulson. When the electric quadrupole moment Q(N14) of the nitrogen nucleus is determined from the experimental nuclear quadrupole coupling constant eQq, all Q(N14) values obtained by us fall into the range of values already found by several authors. The most reliable computed value of Q(N14) may be 0.94×10−26 cm2, which can be obtained from the wave function including configuration interaction given by Kaplan. The polarization effect of the inner shell pointed out by Sternheimer is also evaluated by the use of Slater atomic orbitals. There is some discussion about the bond equivalent orbitals of NH3.