Room temperature nuclear quadrupole resonance study of the molecular mixed crystal p-dichlorobenzene(1-x) p-dibromobenzene(x)

The nuclear quadrupole resonance (NQR) of Cl-35 was measured at room temperature in molecular alloys of PDClB(1-x)PDBrB(x) as a function of the concentration x expressed as a molar fraction of PDBrB. The line shapes were analyzed by the statistical method over the entire concentration range. At low concentrations of the solutes (phase rich in either PDClB or PDBrB), the concentration dependences of the peak, width and shape of the NQR line are satisfactorily explained by resorting to the anisotropic lattice distortion produced by molecular volume difference. The peak frequency behavior at comparable concentrations indicates that the differences in the electronic charge distribution and the decrease in the lattice normal mode frequencies prevail over volume effect. in this concentration range the line shapes are Gaussian and the line widths are proportional to [x(1 - x)](1/2), typical behavior found in a homogeneous system, opposed to a segregated or demixed system. As a result, the NQR frequency shift in this region is very small compared with the line width, and the reporter phase segregation cannot be completely ruled out. (C) 1997 Elsevier Science Ltd. All rights reserved.