A Raman spectroscopic study of the uranyl selenite mineral haynesite

Abstract

The mineral haynesite, a uranyl selenite, has been characterised by Raman spectroscopy at 298 and 77 K. Two bands at 811.5 and 800.2 cm-1 are assigned to the symmetric stretching modes of the (UO2)2+ and (SeO3)2- units respectively. These values give calculated U-O bond lengths of 1.799 and/or 1.801 A. The broad band at 861.8 cm-1 is assigned to the ν3 antisymmetric stretching mode of the (UO2)2+ (calculated U-O bond length 1.813 A). Additional bands are observed in the 77 K spectrum. In the spectroscopy of selenite compounds the position of the antisymmetric stretching vibration occurs at lower wavenumbers than the symmetric stretching mode and thus the band at 746.6 cm-1 is attributed to the ν3 antisymmetric stretching vibration of the (SeO3)2- units. The ν4 and the ν2 vibrational modes of the (SeO3)2- units are observed at 418.5 cm-1 and 472.1 cm-1. Bands observed at 278.3, 257.3 and 218.8 cm-1 are assigned to OUO bending vibrations.