TEMPERATURE AND PRESSURE-DEPENDENCE OF CL-35 NQR IN NACLO3 AND BA(CLO3)2.H2O

Pressure and temperature dependence of Cl-35 nuclear quadrupole resonance (NQR) has been investigated in NaClO3 and Ba(ClO3)2.H2O. NQR frequencies are measured in the temperature range 77-300 K and up to 5 kbar pressure. The torsional frequency of the ClO3 pyramid and its variation with both pressure and temperature are evaluated from the NQR frequencies under the harmonic approximation. In general, the pressure effect on the internal motions is found to be less in Ba(ClO3)2.H2O compared to NaClO3. When the samples are cooled to 77 K the pressure coefficient of NQR frequency becomes nearly zero in sodium chlorate, whereas it retains a value of 6 kHzkbar-1 in barium chlorate. This behaviour follows from the fact that at 77 K, the torsional frequency in NaClO3 is unaffected by the application of pressure while it increases at the rate 12 cm-1 kbar-1 in Ba(ClO3)2.H2O.