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 doub le resonance (ENDOR) data were collected for various calcitic or arago nitic samples of marine origin. The small and isotropic H-1 hyperfine ENDOR splitting (250-350 kHz) is explained by a locally disordered wat er environment for these species. As for the isotropic CO2- and CO3- r adicals in synthetic monohydrocalcite and apatite, the radicals are mo st probably located in the occluded water embedded in these samples, a nd not in the crystal matrix.