Nuclear Quadrupole Coupling in Polyatomic Molecules

The Gaussian-transform method has been applied to the evaluation of the deuteron and nitrogen-14 quadrupole coupling constant (eqQ/h) with the various minimal and extended basis-set SCF—LCAO—MO functions that are available for the linear polyatomic molecules DCN, C2D2, DF2—, and N3—. Comparisons are made between calculations neglecting and including the three-center integral contributions. The coupling constant is found to be quite sensitive to the choice of basis orbitals, particularly those responsible for the form of the valence-shell charge density. This suggests that the quadrupole coupling constant in polyatomic molecules is a useful criterion for testing the wavefunction obtained in approximate calculations. Of particular interest is the variation in the (eqQ/h)D results for DF2—, which points out the need for an experimental coupling constant measurement for this hydrogen-bonded species.