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The vibrations of vitreous silica observed in hyper‐Raman scattering
Author(s) -
Hehlen B.,
Simon G.
Publication year - 2012
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.4110
Subject(s) - raman spectroscopy , molecular vibration , raman scattering , isotropy , cooperativity , molecular physics , symmetry (geometry) , infrared , chemistry , tetrahedron , dipole , local symmetry , scattering , condensed matter physics , crystallography , analytical chemistry (journal) , physics , optics , quantum mechanics , biochemistry , geometry , mathematics , organic chemistry , chromatography
Hyper‐Raman scattering (HRS) is performed in v ‐SiO 2 , and the results are compared to RS and infrared absorption data. Mode analyses are tested based on two models, either the local C 2 v symmetry of the Si–O–Si bonds or the T d symmetry of the SiO 4 tetrahedra. The HRS boson‐peak (BP) signal is dominated by the quasi‐local librations of tetrahedra. However, we find that it also contains a weak dipolar contribution with a different spectral signature, suggesting that the BP modes are not fully hybridized. The transverse optic (TO) modes can be assigned to molecular‐like excitations according to either model, with the exception of the lowest frequency TO4 which involves highly cooperative Si–O–Si motions. On the opposite, the strong scattering from all longitudinal optic (LO) modes clearly follows the average isotropic medium ∞∞ m selection rules. This long range cooperativity presumably results from the associated internal electric field. Finally, the strong LO HRS signals enabled observing a new longitudinal component at 1078 cm −1 . Through the example of v ‐SiO 2 , the article also highlights new perspectives provided by HRS for the description of the vibrations in disordered materials in general. Copyright © 2012 John Wiley & Sons, Ltd.