Electrically Induced Perturbations of Halogen Nuclear Quadrupole Interactions in Polycrystalline Compounds. I. Phenomenological Theory and Experimental Results

When a nucleus in a dielectric solid occupies a lattice site which lacks inversion symmetry, the application of an external electric field causes a change in the electric field gradient at this nucleus. The magnitude of the change is proportional to the applied field. When the nucleus has spin greater than one‐half and possesses a nonzero quadrupole moment, the quadrupole interaction energy is, therefore, a linear function of the applied field. This field gradient perturbation is discussed phenomenologically through the use of a third rank tensor R which relates the electric field and the electric field gradient via the equation eΔq=R·E. Changes in the quadrupole interaction energy, observed as broadenings of nuclear quadrupole resonance lines in zero magnetic field, have been obtained for ³⁵Cl, ⁸¹Br, and ¹²⁷I nuclei in halogenated polycrystalline compounds including several halogenated methanes and benzenes, the solid halogens, and iodic acid. Broadened line shapes, local electric field corrections, and restrictions imposed by nuclear site symmetries are discussed. All observations are consistent with the phenomenological theory.