Abstract
An electron spin resonance absorption spectrum corresponding to S = 12 , I = 32 , and exhibiting orthorhombic symmetry has been observed in γ‐irradiated single‐crystal calcite. At 4.2°K, the spin‐Hamiltonian parameters are gzz = 2.0150 , gxx = 1.9991 , gyy = 1.9910 , Azz = −152 MHz , Axx = 614 MHz, Ayy = −173 MHz , (gnβn/h) = −7.24 × 10−4MHz/Oe , e2qQ = 16.2 MHz , and η ≃ 0 . The paramagnetic defect associated with this spectrum is identified as the AsO22− molecule–ion which is located at carbonate ion sites with its plane coincident with that of the carbonate ions. From the hyperfine structure splittings and the g‐tensor anisotropy, it is deduced that the unpaired electron has approximately 1% 4s, 96% 4p, and 3% 4d character and that it is almost completely localized on the arsenic atom.