Pressure dependence of the chlorine NQR in chloro pyridines

The Cl-35 NQR frequency (nu(Q)) and spin lattice relaxation time (T-1) 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 t he 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 2 (nd) 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 TI in all the three compounds shows a small increas e with pressure, indicating that the relaxation is mainly due to the torsio nal motions.