A Raman spectroscopic study of the uranyl selenite mineral haynesite

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 Å. 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 Å). 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 740.5 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 and 472.1 cm−1. Bands observed at 278.3, 257.3 and 218.8 cm−1 are assigned to OUO bending vibrations.