LOCATION AND MOTION OF ISOTROPIC PARAMAGNETIC CENTERS IN SYNTHETIC MONOHYDROCALCITE

The isotropic CO2- and CO3- centres in CaCO3.H2O were examined with el ectron spin resonance (ESR), electron-nuclear double resonance (ENDOR) and thermogravimetric analysis (TGA). From the absence of anisotropy and the small value of the H-1 ENDOR splitting (approximately 0.3 MHz) , the effect of crushing and/or thermal annealing on the ESR and TGA s pectra, it is concluded that both isotropic centres are located in the occluded water, surrounding the constituent crystallites of the spher ulites. ESR line width and C-13 hyperfine coupling parameter measureme nts yield approximate values for the rotation activation energy (DELTA E(CO3-)<DELTAE(CO2-) with DELTAE approximately 0.2 eV) and for the vib rational frequency (approximately 2.10(12) Hz for CO2-).