A single-crystal proton ENDOR study of the ClO3 centre in γ-irradiated barium perchlorate at 120 K

Abstract

Hyperfine coupling tensors for 24 protons have been determined from ENDOR measurements of the ClO₃ centre trapped in γ-irradiated single crystals of barium perchlorate trihydrate at 120 K. The tensors have small isotropic components and their dipolar components are close to axial so that their interpretation in the point-dipole approximation to reconstruct the proton geometry in the vicinity of the trapped radical is justifiable. The model thus obtained indicates that there is no severe distortion of the crystal structure in the immediate vicinity of the trapped radicals. There are two chemically identical but ENDOR-distinguishable sites related by a reflection in the a₁a₂ plane of the hexagonal crystal. This observation supports the assignment of the P6₃/m space group to the crystal: X-ray diffraction measurements had indicated that the P6₃ space group was also a possibility.