Electron Spin Resonance Absorption Spectrum of the AsO22− Molecule–Ion in <i>γ</i>-Irradiated Single-Crystal Calcite

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.