ESR studies of irradiated single crystals of alkali halides doped with ferrocyanide ion

Single crystals of RbCl, RbBr, and KCl doped with [Fe(CN)6]4− were grown from solution and ESR spectra of both x‐ and γ‐irradiated crystals were recorded over a wide temperature range. A number of Fe(I) radicals were obtained and identified by their ESR spectra. Thermally treated crystals showed the presence of halogen‐substituted radicals. Rotations were made in the crystallographic planes and the spectra analyzed using a suitable spin Hamiltonian including, where appropriate, nitrogen and halogen ligand superhyperfine interactions. Powder spectra were also recorded and used as a cross check on the single crystal analyses. The g and superhyperfine splitting tensors are shown to be consistent with having the odd electron in an antibonding orbital of a1g symmetry made up largely from the metal dz2 orbital. The spin densities in the ligand s and p valence orbitals and the p/s ratios were computed where possible. Structures have been proposed for the various radicals based on the observed ESR parameters.