³⁵Cl NQR studies of 1‐chloro‐2,4‐dinitrobenzene and 1,2‐dichloro‐3‐nitrobenzene as a function of pressure and temperature

Abstract

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.

14N NQR, relaxation and molecular dynamics of the explosive TNT

“…The mean torsional frequency of the para groups is then calculated to be 91 cm -1 and that for the ortho groups should cover a range from approximately 60 to 90 cm -1 . Similar values have been observed in other aromatic nitro compounds [17][18][19][20][21]. Also the terahertz spectrum of TNT [22,23] shows a number of features, broad peaks or inflections, from 60 to 100 cm -1 .…”