Abstract
The vibrational spectra of a series of disordered two-fold coordinated chains of atoms, calculated using bond stretching and bending forces only, are presented. The disorder is included by a distribution in the dihedral angle, the bond angles being set at the value for crystalline Se. Comparison of the results with experimental data for a-Se indicates the existence of a preferred magnitude for the dihedral angle along chain-molecular units. Further considerations suggest the sign of the dihedral angle is constant or random and may be distributed about the crystalline value with a standard deviation up to a maximum of about 10°. It is likely that this distribution is broader in a-Te than in a-Se.