Vibrational spectra of single-crystal topaz

A single-crystal of topaz was studied by Raman spectroscopy to assign the internal modes of the high-frequency range and to compare with infrared data.All active modes exhibit an important Davydov splitting (150 cm−1) but we have found a small Bethe splitting (14.5 cm−1) consistent with a very regular SiO4 tetrahedron. Because of a high value of v1 (∼920 cm−1) the Raman active modes present a mixed v1/v3 character.Finally the substitution of OH for F splits an Ag internal mode and lead to some proper modes at 3650 cm−1, 3639 cm−1 and 1165 cm−1.

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