A Raman Spectroscopic Study of the Uranyl Phosphate Mineral Parsonite

The mineral parsonsite with samples from The Ranger Uranium Mine, Australia and La Faye Mine, Grury, Saone-et-Loire, Burgundy, France has been characterised by Raman spectrocopy at 298 and 77 K and complemented with infrared spectroscopy. Two Raman bands close to 807 and 796 cm-1 are attributed to the ￮1 (UO2)2+ symmetric stretching modes, whilst two bands close to 953 or 945 cm-1 and 863-873 cm-1 are assigned to the ￮3 (UO2)2+ antisymmetric stretching vibrations. Four or five bands (953, 926, 910, 883 cm-1) are observed in the infrared spectrum in this region . Bands at 965-967 and 972 cm-1 are assigned to the ￮1 (PO4)3- symmetric stretching modes and bands that are observed in the 987 to 1078 cm-1 to the ￮3 (PO4)3- antisymmetric stretching modes. Bands at 465, 439, 406, 394 cm-1 (298 K) and 466, 442, 405, 395 cm-1 (77 K) are assigned to the split doubly degenerate ￮2 (PO4)-3 bending vibrations. Bands of very low intensity at 609, 595, 591, 582, 560 and 540 cm-1 are attributed to the split triply degenerate ￮4 (PO4)-3 bending modes. Bands observed at wavenumbers lower than 300 cm-1 are connected with the split ￮2 (￤) (UO2)2+ bending, ￮ (U-Oligand), ￤ (U-Oligand), and lattice vibrations. U-O bond lengths in uranyl are calculated frm the Raman and infrared spectra which are in agreement with those from available X-ray single crystal structure analysis of parsonsite. Short comment is given to the water content and possibility of a hydrogen bonding network in parsonsite crystal structure