A Raman spectroscopic study of alunites

Frost, Ray L., Wills, Rachael-Anne, Weier, Matt L., Martens, Wayde N., & Kloprogge, J. Theo (2006) A Raman spectroscopic study of alunites. Journal of Molecular Structure, 785(1-3), pp. 123-132.

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Abstract

Raman spectroscopy at 298 and 77 K has been used to characterise alunites [M2(Al 3+)6(SO4)4(OH)12 ] where M is the monovalent cations K+, Na+, NH4+. The minerals are characterised by well defined hydroxyl stretching patterns which give two groups of hydrogen bonds with calculated hydrogen bond distances of 2.90 and 2.84-7 Å. The Raman spectrum of alunites shows an intense sharp band at 1026 cm-1 which is cation dependent. Multiple bands attributed to the ν4 bending mode are observed around 655 cm-1 showing a reduction in sulphate symmetry from D53d to C3v. This symmetry reduction is confirmed by the observation of multiple bands in the 480 to 508 cm-1 region ascribed to ν2 bending modes. Intense bands are observed at 563 cm-1 (K-alunite) 576 cm-1 (Na-alunite) and 564 cm-1 (H3O+alunite) assigned to an OH deformation vibrations. Intense bands are observed at 235 cm-1 (K-al), 238 cm-1 (Na-al) and 235 cm-1 (NH4-al) attributed is to OH…O hydrogen bond stretching. Raman spectroscopy enables the differentiation between the alunites synthesised with different cations.

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ID Code: 3690
Item Type: Journal Article
Refereed: Yes
Additional Information: This paper is one of a series of papers on alumites and jaorosites. These minerals have been identified on the planet Mars. The presence of these minerals gives credence to the presence of water on mars either in the present or the past, since such minerals are only formed from solution
Keywords: alunite, natroalunite, ammonioalunite, jarosite, Raman spectroscopy, sulphate
DOI: 10.1016/j.molstruc.2005.10.003
ISSN: 0022-2860
Divisions: Past > QUT Faculties & Divisions > Faculty of Science and Technology
Copyright Owner: Copyright 2006 Elsevier
Copyright Statement: Reproduced in accordance with the copyright policy of the publisher.
Deposited On: 09 Mar 2006 00:00
Last Modified: 29 Feb 2012 13:24

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