The application of a pulsed F.T. NQR system in the investigations of SbCl₃ and GaCl₃ has revealed fine structures in the Zeeman split lines. Each of the Zeeman split lines due to ³⁵Cl in SbCl₃ has been found to be a doublet and in the case of GaCl₃ each line has been observed as a triplet or a quadruplet. The NQR Zeeman studies by the pulsed spectrometer has been realised by the development of a number of programs in Assembler language for the increment of S/N ratio and resolution of the spectra, FFT of the time varying signals and the automation of the measurements. The parameters of the electric field gradient tensor, at the site of the different nuclei, are derived from the data of the Zeeman split spectra, for rotation of the crystal about a single axis, utilising a minimization program in FORTRAN.

These fine structures in Zeeman split lines are interpreted to be of isotopic origin. There appears to be both a frequency shift and an angular displacement which in GaCl₃ is as much as 0-77°