Nuclear Hyperfine Coupling Constants of Diphenyl Picryl Hydrazyl

Two groups of single crystals of diphenyl picryl hydrazine (DPPH2) have been grown from organic solvents. The samples of one group contain large concentrations of residual solvent molecules and those of the other group, practically negligible concentrations of solvent molecules. Diphenyl picryl hydrazyl (DPPH) molecules have been produced in the samples by irradiating with thermal neutrons. The anisotropy of the observed electron paramagnetic resonance (EPR) spectra of DPPH in the samples of the first group has been found to be different from EPR spectra of DPPH in the samples of the second group. However, satisfactory interpretations of the anisotropies have been obtained in terms of the principal values of the hyperfine tensors of DPPH determined previously by Holmberg et al. It appears that different species of molecules neighboring DPPH molecules and varying concentration of residual solvent molecules in the host crystals do not affect noticeably the principal values of the tensors.