A pulsed Cl-35 NQR study on the molecular motions and phase transition of 4-chlorobenzyl alcohol

The spin-lattice and spin-spin relaxation times T-1 and T-2 of Cl-35 NQR were measured for the high (I) and low (II) temperature phases of 4-chlorobenzyl alcohol in the range 50 < T/K < 338 (transition and melting points: 236 and 343.5 K, respectively). In phase II the T-1 behavior in the range 50 < T/K < 90 can be explained by lattice vibrations and that in the range 90 < T/K < 190 by reorientation with an activation energy of ca. 3.8 kJ/mol. In phase I, the T-1 behavior at T > 260 K is explainable by another reorientation with E(a) approximate to 4.7 kJ/mol. The T-1 vs. T curves revealed that in both phases the crystal dynamics is anomalous in the vicinity of the transition temperature. Lattice defects accumulated in phases I and II by the phase transition were found to be responsible for the extremely short inverse line width parameters (T-2*).