Hyper-Raman scattering analysis of the vibrations in vitreous boron oxide

Hyper-Raman scattering has been measured on vitreous boron oxide, v-B2O3. This spectroscopy, complemented with Raman scattering and infrared absorption, reveals the full set of vibrations that can be observed with light. A mode analysis is performed based on the local D-3h symmetry of BO3 triangles and B3O3 boroxol rings. The results show that in v-B2O3 the main spectral components can be successfully assigned using this relatively simple model. In particular, it can be shown that the hyper-Raman boson peak arises from external modes that correspond mainly to librational motions of rigid boroxol rings.