Hyperfine structure in Ga NQR of Gas and GaSe

Fine structure is reported in the ^69,71Ga NQR spectra of GaS and GaSe. The ⁶⁹Ga (I = ³₂) and ⁷¹Ga (I = ³₂) spectra are $\text{qualitatively}$ different for each compound. This is attributed to an indirect spin-spin interaction between nearest-neighbour Ga atom pairs. A model giving reasonable quantitative agreement with experiment is presented.