Quadrupole effects in the electron spin echo from pairs of diphenylnitryl radicals

This analysis of ESE modulation effects for DPN pairs indicates that the frequencies are those of quadrupole resonance for the nitrogen atoms in the DPN in the external magnetic field, and this has enabled us to determine the quadrupole splitting parameters. However, an exact calculation on the NQR transition frequencies in the partially oriented system requires a knowledge of the directions of the electric field gradient tensor axes, which cannot be derived from these experiments. For this reason, in a study of this type one must make the fullest possible use of data from other experiments or from quantum-chemical calculations, which should enable one to restrict the possible directions for the EFG tensor axes.