Structure and bonding in the mixed chalcogenide system As2SxSe3?x

⁷⁵As Nuclear Quadrupole Resonance (NQR) lineshape measurements for the amorphous mixed chalcogenide system As₂S_xSe_3?x are reported. The line-shapes are asymmetric and approximately 8 MHz in width (full width at half maximum). The peak resonance frequency is observed to increase approximately linearly with x. The NQR results indicate the presence of mixed As₂(S, Se)₃ pyramidal structural units and are thus not consistent with models that predict the occurrence of anion subsite segregation. NQR measurements performed on crystalline As₂SSe₂ lend support to the structural model proposed for the glasses.