Location and Motion of Isotropic Paramagnetic Centres in Synthetic Monohydrocalcite

Abstract

The isotropic CO-2 and CO-3 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 1H ENDOR splitting ( ∼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 13C hyperfine coupling parameter measurements yield approximate values for the rotation activation energy (ΔE( CO3-<ΔE( CO2-) with ΔE∼ 0.2 eV) and for the vibrational frequency ( ∼2.1012 Hz for CO2-).