The 35C1 Nuclear Quadrupole Resonance (NQR) frequency ( V q ) and spin lattice relaxation time (T{) in the three anisoles 2,3,4-trichloroanisole, 2,3,6-trichloroanisole and 3,5-dichloroanisole have been measured as a function of pressure upto 5.1 kbar at 300 K, and the data have been analysed to estimate the temperature coefficients of the NQR frequency at constant volume. All the three com pounds show a non linear variation of the NQR frequency with pressure, the rate of which is positive and decreases with increasing pressure. In case of 3,5-dichloroanisole the value becomes negative in the higher range of pressure studied. The spin lattice relaxation time T{ in all the three compounds shows a weak dependence on pressure, indicating that the relaxation is mainly due to the torsional motions.

The (35)Cl nuclear quadrupole resonance (NQR) frequencies (nu(Q)) in caesium and sodium chlorates were measured as a function of temperature, from 77 to 300 K at different pressures up to 5.1 kbar, and the data were analysed to estimate the volume dependence of the electric field gradient (EFG), torsional frequency and also the contributions to the NQR frequency from static and dynamic effects. The variation of spin-lattice relaxation time with pressure at different temperatures was studied in the case of sodium chlorate and at room temperature in case of caesium chlorate. The pressure dependence of the spin-lattice relaxation time (T(1)) suggests that the relaxation is mainly due to the torsional motions.

The temperature and pressure dependences of 35 Cl nuclear quadrupole resonance (NQR) frequency and spin-lattice relaxation time (T 1 ) were investigated for 1-chloro-2,4-dinitrobenzene and 1,2-dichloro-3-nitrobenzene. T 1 was measured in the temperature range 77-300 K. Furthermore, the NQR frequency (n) and T 1 for these compounds were measured as a function of pressure up to 5.1 kbar at 300 K. Relaxation was found to be due to the torsional motion of the molecule and the reorientation motion of the nitro group. By analysing the temperature dependence of T 1 , the activation energy for the reorientation motion of the nitro group was obtained. The temperature dependence of the average torsional lifetimes of the molecules and the transition probabilities W 1 and W 2 for the 1m = ±1 and 1m = ±2 transitions, were also obtained. Both compounds showed a non-linear variation of NQR frequency with pressure. The pressure coefficients were observed to be positive. A thermodynamic analysis of the data was carried out to determine the constant-volume temperature coefficients of the NQR frequency. The spin-lattice relaxation time T 1 for both the compounds was found to be weakly dependent on pressure, showing that the relaxation is mainly due to the torsional motions.

The proton spin-lattice relaxation time (T,) has been measured in methylammonium hexabromoplumbate, (CH,NH3),PbBr6, in the range 77-4503 and tetramethylammonium ("MA) hexachloroselenate, [N(CH,),I2SeCI6 in the range 77-430K In (CH3NH3)*PbBr,, TI shows a slope change at 415K, a minimum at 215K, and a discontinuous jump at 167K In [N(CH,)&SeCl6, TI shows a slope change at 340K and goes through a narrow symmetric minimum at 194K. Further, it exhibits a shoulder-like structure at 106K and goes through a broad minimum at 85K. Motional parameters such as activation energy and preexponential factor have been evaluated for the reorientational motion of CH,-NH, groups and the TMA ion in different phases.

The 35CI NQR frequency (υQ) and spin lattice relaxation time (T1 ) in 2,6-dichloropyridine, 2 amino 3,5-dichloropyridine and 6 chloro 2-pyridinol have been measured as a function of pressure up to 5.1 kbar at 300 K, and the data have been analysed to estimate the temperature coefficients of the NQR frequency at constant volume. All the three compounds show a non linear variation of the NQR frequency with pressure which can be described by a 2nd order polynomial in pressure. The rate of change of the NQR frequency with pressure is positive and decreases with increasing pressure. The spin lattice relaxation time T1, in all the three compounds shows a small increase with pressure, indicating that the relaxation is mainly due to the torsional motions.