14N Quadrupole Resonance in the presence of a weak static magnetic field. Direct determination of the electric field gradient tensor

The electric field gradient tensor (considered here at the level of a nitrogen nucleus) can be described by two parameters: the largest element in the (x, y, z) principal axis system, denoted by V zz , and the asymmetry parameter η = ( V yy - V xx ) / V zz . The frequencies of the three nitrogen-14 NQR transitions depend on both parameters and two of them are, a priori, necessary for their determination. We demonstrate that, if a weak static magnetic field is applied during a NQR experiment, both parameters can be obtained from a single transition thus alleviating the difficulties for finding out 14N Quadrupole Resonance lines.