ESR study of paramagnetic centers in irradiated Ba(ClO3)2 · H2O · and Ba(ClO3)2 · D2O single crystals

ESR study of γ‐irradiated Ba(ClO₃)₂ · H₂O revealed three main centers which are identified as ${\mathrm{O}}_3^{-}$ , ClO₂, and (ClO₂–H₂O) radicals, trapped at two distinct sites. The parameters of the spin Hamiltonian have been determined from single crystal and powdered samples. The principal values for ${\mathrm{O}}_3^{-}$ and ClO₂ centers agree with those reported in other systems. The chlorine center having ``superhyperfine'' interaction with the two protons of water of crystallization has been identified as a (ClO₂–H₂O) radical. The principal values of the g tensor are g_xx=2.0023, g_yy=2.0065, and g_zz=2.0150; those of the A tensor are a_xx=102.11, a_yy=53.22, and a_zz=7.79 G. The parameters of the hyperfine coupling of ³⁵Cl with the first proton are a_xx=8.6, a_yy =5.0, and a_zz=5.0 G, with a_iso=6.2 G, and those for the second proton are a_xx=2.5, a_yy=1.2, and a_zz=1.2 G. The (ClO₂–H₂O) center is found to be bleached at temperatures (above 120°C), where the crystal loses its water of hydration. On exposing the irradiated crystal to uv light, the two chlorine centers ClO₂ and (ClO₂–H₂O) are fully bleached, followed by an increase in the concentration of the ${\mathrm{O}}_3^{-}$ center.