H-1 AND P-31 ENDOR OF THE ISOTROPIC CO2- SIGNAL AT G=2.0007 IN THE EPR-SPECTRA OF PRECIPITATED CARBONATED APATITES

The isotropic EPR signal at g = 2.0007 in X-irradiated carbonated apatites, precipitated from aqueous solutions and dried at 25 degrees C, is investigated with Electron Nuclear Double Resonance (ENDOR). The Na-23, P-31 and H-1 ENDOR results indicate that the precursor of this radical is most probably located in an aqueous phase entrapped between the crystallites (the so-called occluded water). Other experimental features, such as the correlation between the appearance of the signal in the EPR spectrum and the presence of some residual (adsorbed and/or occluded) water in the sample seem to strengthen our hypothesis.