35Cl nuclear quadrupole resonance studies of molecular motions of ClO3- and water diffusion in Ca(ClO3)2.2H2O

A 35Cl nuclear quadrupole resonance (35Cl-NQR) investigation of polycrystalline Ca(ClO3)2.2H2O is described. The 35Cl-NQR frequencies (vQ) for two resonance lines (vQ1 and vQ2), the spin lattice relaxation time (T1Q) for vQ2 only and the line width delta vQ2 were measured in the temperature range 292-345 K, except for the frequency measured up to 455 K. The observed decrease in the resonance frequencies with increasing temperature permitted the determination of the frequencies of librations of the ClO3- ion about two axes perpendicular to the three-fold axis of the ion mainly responsible for this effect. The temperature dependence of the relaxation time T1Q proved the occurrence of water diffusion and hindered rotation of ClO3- ions. The activation energies of these two molecular motions were determined, and their effect on the electric field gradient at the site of a chlorine nucleus was discussed. Temperature measurements of the line width delta vQ2 confirmed the conclusions drawn from the analysis of T1Q(T).