ESR and Optical Absorption Studies of ClO₃ in Ba(ClO₄)₂ · 3H₂O Single Crystals

Abstract

The CIO, radical observed in y-irradiated Ba(CIO,), . 3 H,O is studied by ESR and optical absorption techniques. The radical orientation and stability with increased irradiation and thermal and UV light bleaching are discussed. A temperature variation study by ESR reveals that there is an increase of 13.8% and a decrease of 4% in the chlorine p-orbital and s-orbital spin densities, respectively, when the temperature is lowered from 300 to 77 K. A comparison of the results obtained for CIO, with the other iso-electronic trioxide radicals shows that the maximum fractional change in the spin densities occurs in the case of CIO, and that these changes depend on the electronegativity of the central atom. IntrodactionThe presence of the C10, radical in X-or y-irradiated perchlorates and chlorates [l to 61 has been well established in earlier studies. Though the host lattice dependence of the stabilities of paramagnetic radicals is well known, the stability of C10, was studied only in a few lattices [3,5, 61. Besides, there is no report on the study of the temperature variation of the magnetic parameters of this radical, though such studies were reported for C10, [7]. These studies give an understanding of the structural changes of the radical as well as the effects of molecular and lattice vibrations.Recently we reported the proton spin-flip satellite lines associated with the C10, radical in Ba(C10,), . 3 H,O [S]. I n the present paper we discuss the orientation, the effect of increased y-irradiation, thermal and UV light induced reactions, and the temperature dependence of the hyperfine coupling constants of this radical. These investigations may help in understanding the effect of the present lattice on the stability and behaviour of the C10, radical besides the effect of structural changes or niolecular and lattice vibrations on its spin Hamiltonian. Crystal StructureThe crystal structure of Ba(C10,), -3 H,O is hexagonal biniolecular with unit cell dimensions a = 0.72944 nm and c = 0.96744 nm. The X-ray crystallographic study l) Madras 600036, India.') On sabbatical leave till June 1982 a t the Physikalische Chemie 111,