Electron spin resonance (ESR), electron nuclear double resonance (ENDOR) and general triple resonance of irradiated biocarbonates

Several irradiated bicarbonates were studied by magnetic resonance techniques. Seven paramagnetic species, attributed to CO2-, SO2- and SO3- were identified. Comparison between radiation induced defects in bioaragonites and aragonite single-crystals show that isotropic and orthorhombic CO2-centers with broad line spectra are not produced in the latter samples. Vibrational and rotational properties of isotropic CO2- centers were studied from low temperature Q-band spectras. Vibrational frequency is determined from the 13CO2- hyperfine spectrum and yielded ν 1.54 x 1013 s-1. The correlation time for isotropic CO2-, τc) = 1.2 x 10-11s (T = 300 K0, is typical of radicals rotating in liquids. ENDOR and General Triple spectroscopy show that orthorhombic CO2- centres are surrounded by water molecules located in the second nearest CO22- sites at 5.14, 5.35 and 6.02 A. Water molecules replacing carbonates or as liquid inclusion of growth solution in local crystal imperfections may be responsible for the variety of orthorhombic and isotropic CO2- species, respectively. (author)