US EPA

4189208 

Journal Article 

The Lattice Dynamics of Mercuric Chloride 

Keartland, JM; Newby, E 

2012 

85-90 

WOS:000367878700015 

Measurements of the nuclear spin-lattice relaxation time (T-1) of the Cl-35 nuclei in a high purity sample of the molecular solid mercuric chloride (HgCl2) have been made over the temperature range 9 K - 485 K using pure nuclear quadrupole resonance (NQR). Spin-lattice relaxation in this material appears to be dominated by lattice vibrations and/or molecular librations over the entire temperature range investigated. Analysis of the data using available spin-lattice relaxation models has allowed us to estimate the Debye temperature, and to follow changes in the lattice dynamics as a function of temperature. At temperatures above 340 K deviations from the expected quadratic relationship between the spin-lattice relaxation rate and temperature have been noted. Further analysis shows this is a thermally activated process related to the HgCl2 molecules changing their position in a double-well potential. A previously unobserved doublet in the NQR spectrum of the Cl-35 nuclei was seen at temperatures above 340 K. The perturbation underlying the changed line-shape appears to be related to hindered re-orientations of the HgCl2 molecules in the crystal lattice. The correlation time of the perturbation was calculated for a range of temperatures. The temperature dependence of the correlation time may be understood by noting the fact that the structure of the unit cell of the lattice is temperature dependent. We conclude that there is a correlation between the high temperature T-1 results and the doublet observed in the NQR spectrum.