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It has been proposed that the sharp Raman lines seen in vitreous SiO₂ and other glasses are the signatures of highly regular rings of bonds connected into a more disordered network. We derive a condition for vibrational decoupling of the appropriate ring modes from the surrounding network, and thereby explain both the anomalously narrow linewidths and the absence of Si isotope shifts. The results encourage the development of vibrational spectroscopy as a probe of intermediate-range order in the form of regular rings in amorphous solids.
Galeener et al. (Mon,) studied this question.