Electron Spin Resonance Absorption Spectra of CO3− and CO33− Molecule—Ions in Irradiated Single-Crystal Calcite

Abstract

Single crystals of x- and γ-irradiated calcite reveal a number of paramagnetic defect centers, two of which have been tentatively identified as the CO3− and CO33− molecule—ions. The ESR absorption spectrum of what is believed to be the CO3− molecule—ion is found to have symmetry about the calcite [111] direction with spin-Hamilton parameters given by g‖=2.0051, g⊥=2.0162, A‖=13.1 Oe, and A⊥=9.4 Oe. The corresponding parameters for what is believed to be the CO33− molecule—ion which also exhibits symmetry about the crystal [111] direction are given by g‖=2.0013, g⊥ =2.0031, A‖=171.22 Oe, and A⊥=111.33 Oe. The parameters of these two spectra are discussed and compared with those reported for the isoelectronic NO3 and NO32− species. Optical measurements reveal two absorption bands, one at 6500 Å and another at 4850 Å. The longer-wavelength band exhibits anisotropy and is found to have temperature-dependent decay characteristics which are similar to those of the CO3− molecule—ion ESR spectrum. An activation energy of 0.12 eV is obtained for this center. Thermal decay data suggest that the shorter-wavelength band is not associated with either of these paramagnetic species.