An electron nuclear double resonance and electron spin resonance study of isotropic CO2- and SO2- radicals in natural carbonates

Natural samples often exhibit isotropic electron spin resonance (ESR) signals at g=2.0006, (CO2-) and g=2.0057 (SO2-). Electron nuclear double resonance (ENDOR) data were collected for various calcitic or aragonitic samples of marine origin. The small and isotropic H-1 hyperfine ENDOR splitting (250-350 kHz) is explained by a locally disordered water environment for these species. As for the isotropic CO2- and CO3- radicals in synthetic monohydrocalcite and apatite, the radicals are most probably located in the occluded water embedded in these samples, and not in the crystal matrix