ESR studies of Cl2- (VK) centre trapped in irradiated Ca(ClO3)2 . 2H2O single crystals

A Cl₂- centre has been trapped in X or γ-irradiated Ca(ClO₃)₂. 2H₂O single crystals at 298 K, when the irradiated crystals were illuminated with ultra-violet light (360 nm). This centre is formed at the expense of ClO₂ centres in this crystal. This Cl₂ ^- centre is trapped at two magnetically inequivalent sites in the crystal lattice and these sites become equivalent when the static magnetic field is parallel or perpendicular to the b axis. At many orientations this centre reveals ‘super-hyperfine’ interaction with a proton (I = 1/2) of the water of crystallization. The magnetic parameters are close to those observed in alkali chlorides and the E.S.R. spectrum has been fitted to an orthorhombic spin hamiltonian. The principal g values are g_xx = 2·035, g_yy = 2·033 and g_zz = 2·000 and those of the A values are A_xx = 15·0, A_yy = 31·0 and A_zz = 109·0 G. The shfs parameters are A _‖' = 5·0 A _⊥' = 1·0 G. The V_K centre trapped in this lattice is exceptionally stable at room temperature.