Electron Spin Resonance (ESR), Electron Nuclear Double Resonance (ENDOR) and General Triple Resonance of Irradiated Biocarbonates

摘要

Several irradiated biocarbonates were studied by magnetic resonance techniques. Seven paramagnetic species, attributed to CO_2~- SO_2~- and SO_3~- were identified. Comparison between radiation induced defects in bioaragonites and aragonite single-crystals shows that isotropic and orthorhombic CO_2~- centers with broad line spectra are not produced in the latter samples. Vibrational and rotational properties of isotropic CO_2~- centers were studied from low temperature Q-band spectra. Vibrational frequency is determined from the °COf hyperfine spectrum and yielded v = 1.54 X 10~(13) s~(-1). The correlation time for isotropic CO_2~- τ_c = 1.2 X 10~(-11)s (T = 300 K), is typical of radicals rotating in liquids. ENDOR and General Triple spectroscopyshow that orthorhombic CO_2~- centers are surrounded by water molecules located in the second nearest CO_3~(2-) sites at 5,14, 5.35 and 6.02 A. Water molecules replacing carbonates or as liquid inclusion of growth solution in local crystal imperfectionsmay be responsible for the variety of orthorhombic and isotropic COf species, respectively.