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

Raman spectroscopy at 298 and 77K has been used to study the mineral kamotoite-(Y), a uranyl rare earth carbonate mineral of formula Y2(UO2)4(CO3)3(OH)8. 10-11H2O. The mineral is characterised by two Raman bands at 1130.9 cm-1 and 1124.6 cm-1 assigned to the ν1 symmetric stretching mode of the (CO3)2- units, while those at 1170.4 and 862.3 cm-1 (77 K) to the ￤ 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 ν2 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 ν1 symmetric stretching mode of the (UO2)2+ units and the second band at 809.6 cm-1 is due to the ν2 bending modes of the (CO3)2- units. Bands observed at 584 and 547.3 cm-1are attributed to water librational modes. An intense band at 417.7 cm-1 resolved into two components at 422.0 and 416.6 cm-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 ν2 (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