ELECTRON-SPIN-RESONANCE, ELECTRON-NUCLEAR DOUBLE-RESONANCE AND GENERAL TRIPLE-RESONANCE STUDIES ON THE CONTRIBUTIONS TO LINE BROADENING OF CO2- IN A-TYPE CARBONATED APATITES AND BIOCARBONATES

Electron spin resonance (ESR), electron-nuclear double resonance (ENDO R) and general triple resonance were combined to study linewidth diffe rences observed in the ESR spectra of CO2- species in calcium carbonat e and carbonated apatite. In the latter compound, the motion and a dis tribution of g-factors (g-strain) are dominant contributions to the ob served linewidth. The linewidth temperature behavior follows previous models for CO2- rotating in calcite. In apatite, these radicals rotate more freely and movement is not restricted to g(xx) - g(zz) plane. In carbonates theoretical fit of the linewidth at 9.5 and 34.0 GHz shows the existence of two orthorhombic spectra with slightly different g v alues and linewidths, which contribute to the observed linewidth diffe rence between narrow and broad line species. Superhyperfine interactio ns with protons of water molecules, located probably near the second a nd the third nearest neighbor lattice sites, are responsible for minor contributions to line broadening of CO2- spectrum.