In the electron paramagnetic resonance spectra of single copper impurity ions and their dimer associates in a BaF2 single crystal, an anomalous change in the relative amplitude of the resonance lines has been detected upon changing the orientation of the external magnetic field relative to the crystallographic axes. This effect is presumably attributed to quantum interference between the probability amplitudes of magnetic dipole and electric quadrupole resonant transitions simultaneously excited between the electron spin states of a dimer associate.
Zaripov et al. (Sun,) studied this question.