Raman spectroscopy of uranyl rare earth carbonate kamotoite-(Y)

Raman spectroscopy at 298 and 77 K has been used to study the mineral kamotoite-(Y), a uranyl rare earth carbonate mineral of formula Y-2(UO2)(4)(CO3)(3)(OH)(8)(.)10-11H(2)O. The mineral is characterised by two Raman bands at 1130.9 and 1124.6cm(-1) assigned to the v, symmetric stretching mode of the (CO3)(2-) units, while those at 1170.4 and 862.3 cm(-1) (77 K) to the delta U-OH bending vibrations. The assignment of the two bands at 814.7 and 809.6 cm(-1) is difficult because of the potential overlap between the symmetric stretching modes of the (UO2)(2+) units and the v(2) bending modes of the (CO3)(2-) units. Only a single band is observed in the 77 K spectrum at 811.6 cm(-1). One possible assignment is that the band at 814.7 cm(-1) is attributable to the v(2) symmetric stretching mode of the (UO2)(2+) units and the second band at 809.6 cm(-1) is due to the v(2) bending modes of the (CO3)(2-) units. Bands observed at 584 and 547.3 cm(-1) are attributed to water librational modes. An intense band at 417.7 cm(-1) resolved into two components at 422.0 and 416.6cm(-1) in the 77 K spectrum is assigned to an Y2O2 stretching vibration. Bands at 336.3, 286.4 and 231.6 cm(-1) are assigned to the v(2) (UO2)(2+) bending modes. U-O bond lengths in uranyl are calculated from the wavenumbers of the uranyl symmetric stretching vibrations. The presence of symmetrically distinct uranyl and carbonate units in the crystal structure of kamotoite-(Y) is assumed. Hydrogen-bonding network related to the presence of water molecules and hydroxyls is shortly discussed. (c) 2005 Elsevier B.V. All rights reserved.