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 $g_{\Vert }{\text{=2.0051, g}}_{\perp }{\text{=2.0162, A}}_{\Vert }\text{=13.1\hspace{0.17em}}\mathrm{Oe},\mathrm{and}{\mathrm{\hspace{0.17em}A}}_{\perp }\text{=9.4\hspace{0.17em}}\mathrm{Oe}$ . 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 $g_{\Vert }{\text{=2.0013, g}}_{\mathrm{\perp \hspace{0.17em}}}{\text{=2.0031, A}}_{\Vert }\text{=171.22\hspace{0.17em}}\mathrm{Oe},\mathrm{and}{A}_{\perp }\text{=111.33\hspace{0.17em}}\mathrm{Oe}$ . 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.