Multifrequency EPR study on radiation induced centers in calcium carbonates labeled with ¹³C

In calcite and aragonite, γ-irradiated at 77 K, several paramagnetic centers were generated and detected by EPR spectroscopy; in calcite, CO₃⁻ (orthorhombic symmetry, bulk and bonded to surface), CO₃³⁻, NO₃²⁻, O₃⁻, and in aragonite CO₂⁻ (isotropic and orthorhombic symmetry) depending on the type of calcium carbonate used. For calcium carbonates enriched with ¹³C more detailed information about the formed radicals was possible to be obtained. In both natural (white coral) and synthetic aragonite the same radicals were identified with main differences in the properties of CO₂⁻ radicals. An application of Q-band EPR allowed to avoid the signals overlap giving the characteristics of radical anisotropy.