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The broadening produced by 2,5-dichloropyridine and 3,6-dichloropyridazine in p-dichlorobenzene has been measured. Theoretical estimates of the broadening are obtained using both a simple model and a Monte Carlo approach. Because of the small size difference between host and impurity molecules, it is concluded that the electric dipole moment can have a very significant effect on the broadening of the NQR line.

Variations of T2★ of the n.q.r. signals of 35Cl, 81Br and 127I in their p-dihalobenzenes were observed to depend on the previous history of the sample. Zonerefined samples were cooled from the melt to room temperature, XXX20°C, in two ways (a) slowly over several hours and (b) quickly over a few minutes. Samples (a) gave higher T2★ values because the fewer crystal defects produced in the slowcooling process gave a more homogeneous electric field gradient. The results gave new measurements of T2★ , emphasized the need for describing past history when quoting linewidth measurements and showed the importance of T2★ measurements in the study of phase transitions.

One of the major broadening mechanisms in Nuclear Quadrupole Resonance is the spread in the electric field gradient produced by defects in the crystal. If the defects are randomly distributed, the electric field gradient follows a normal distribution and the resulting lineshape is symmetrical. This paper shows that asymmetric lineshapes may be produced when the asymmetry parameter of the field gradient is equal to or very close to its extreme values of zero or one even though the field gradient distribution is random. Diagrams of some possible lineshapes are given.

The major broadening mechanism in Nuclear Quadrupole Resonance is the spread in the electric field gradient produced by crystal defects. In multilevel spin systems, the frequencies of the various possible resonances are different functions of the components of the electric field gradient. This paper examines the role of both the principal component of the field gradient and the asymmetry component in the relationship between the linewidths of the two resonances of I = 5 2 nuclei. Comparison with experimental data shows various ways in which defects interact with quadrupolar nuclei.