LOCATION AND MOTION OF ISOTROPIC PARAMAGNETIC CENTERS IN SYNTHETIC MONOHYDROCALCITE

The isotropic CO2- and CO3- centres in CaCO3.H2O were examined with electron 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 spectra, it is concluded that both isotropic centres are located in the occluded water, surrounding the constituent crystallites of the spherulites. ESR line width and C-13 hyperfine coupling parameter measurements yield approximate values for the rotation activation energy (DELTAE(CO3-)<DELTAE(CO2-) with DELTAE approximately 0.2 eV) and for the vibrational frequency (approximately 2.10(12) Hz for CO2-).