Molecular orbital calculations of vibrations in three-membered aluminosilicate rings
Abstract
Ab initio, molecular orbital calculations at the 3 21G* level were carried out on H6Si3O9, [H6Si2AlO2]1-, [H6SiAl2O9]2-, and [H6A13O9]3- cyclic molecules in order to determine their structures and vibrational frequencies. These three-membered rings were found to have minima in their potential energy surfaces indicating stability of the species. The H6Si3O9 ring was found to be slightly non-planar, but the [H6SiAl2O9]2- and [H6Al33O9]3- configurations are more planar. Vibrational frequencies of the Raman-active, bridging oxygen “breathing” modes increase with Si4+ content. Galeener's (1982a, b) assignment of the D2 peak (606 cm-1) in the Raman spectrum of vitreous silica to an oxygen breathing mode in rings of three SiO4 tetrahedra is reconfirmed. Correlation of the ring breathing mode frequencies as a function of (AI/AI + Si) with Raman peaks in the SiO2-NaAlSiO4 system is high. Three-membered aluminosilicate rings are likely to exist and give rise to Raman peaks between 540 and 600 cm-1 in fully-polymerized aluminosilicate glasses.
- Publication:
-
Physics and Chemistry of Minerals
- Pub Date:
- January 1993
- DOI:
- 10.1007/BF00202975
- Bibcode:
- 1993PCM....19..381K