Interpretation of Nuclear Quadrupole Coupling in Nitrogen Containing Molecules with Ab Initio Molecular-Orbital Wavefunctions

Electric field gradients were computed at the nitrogen nuclei in a number of small molecules, using LCAO MO SCF wavefunctions constructed with Gaussian‐lobe basis sets. Comparisons with molecular‐quadrupole‐constant data leads to a number of independent values for the quadrupole moment of ¹⁴N, which was poorly known. From this work, and other current studies, the best value of ${\mathrm{Q(}}^{14}\mathrm{N)}$ is 1.56 × 10⁻²⁶ cm². The contributions to the electric field gradient from various molecular orbitals are analyzed in detail for several cases. Procedures for estimating field gradients with the aid of overlap integrals are critically examined.