Raman and infrared spectroscopic study of the molybdate-containing uranyl mineral calcurmolite

Raman and infrared spectra of calcurmolite were recorded and interpreted from the uranium and molybdenum polyhedra, water molecules and hydroxyls point of view. U-O bond lengths in uranyl and Mo-O bond lengths in MoO6 octahedra were calculated and O-H…O bond lengths were inferred from the spectra. The mineral calcurmolite is characterised by bands assigned to the vibrations of the UO2 units. These units provide intense Raman bands at 930, 900 and 868 and 823 cm-1. These bands are attributed to the antisymmetric and symmetric stretching modes of the UO2 units respectively. Raman bands at 794, 700, 644, 378 and 354 cm-1 are attributed to vibrations of the MoO4 units. The bands at 693 and 668 cm-1 are attributed to antisymmetric and symmetric Ag modes of terminal MO2 units. Similar bands are observed at 797 and 773 cm-1 for koechlinite and 798 and 775 cm-1 for lindgrenite. It is probable that some of the bands in the low wavenumber region are attributable to the bending modes of MO2 units