Mutual Orientations of the Principal Axes of the Electric-Field Gradient Tensors on 14N and 81Br by Combined Zeeman-Effect Measurements in a Single Crystal of p-Bromoaniline

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Abstract
The Zeeman effect of the nuclear quadrupole resonance of both 14N and 81Br nuclei in a single crystal of p‐bromoaniline was studied. The precision of the technique used here is far greater than that of the few previous works in this field. Measurements were made by means of a newly designed spectrometer, working at both 14N and 81Br NQR frequencies, in which the radio‐frequency assemblies could be interchanged without affecting the crystal position. The relative orientation of the electric‐field gradient tensors at the sites of the nitrogen and bromine nuclei were directly determined. The results are interpreted in terms of known relations between the orientations of the field gradient tensor and the bond directions. The conclusion reached is that the amino group should be nearly coplanar with the benzene ring. Also observed was a large effect on line intensity as a function of the orientation and intensity of the static magnetic field H0 arising from nuclear dipole‐dipole coupling between 14N and the 1H nuclei of the amino group.