Molecular models are constructed for large structural units appropriate to ${\mathrm{As}}_x{\mathrm{S}}_{1-x}\left({\mathrm{Se}}_{1-x}\right)$ glasses near $x=0.4\mathrm{}$. The models are similar to those previously constructed for ${\mathrm{Ge}}_y{\mathrm{S}}_{1-y}\left({\mathrm{Se}}_{1-y}\right)$ glasses near $y=0.33\mathrm{}$. Comparison of the models explains anomalies in the temperature and pseudobinary alloying dependence of diffraction data. Anomalies in the Raman scattering from local vibrational modes, particularly at low frequencies, are also resolved by the models. As a byproduct, the model explains the bimodal quadrupolar asymmetry of As${\mathrm{Se}}_3$ pyramidal glass units.

• Received 26 July 1979

DOI:https://doi.org/10.1103/PhysRevB.21.5724