STUDY OF VIBRATIONAL-SPECTRA OF LANTHANUM SULFATE NONAHYDRATE AT DIFFERENT TEMPERATURES IN THE REGION FROM 4000-50 CM(-1)

Infrared spectra of lanthanum sulphate nonahydrate are studied over th e 4000-50 cm-1 range. The bands pertaining to different internal and e xternal modes of sulphate ion and water molecules are observed and ass igned. It is shown that coordinated water molecules exist at two site symmetries C1 and C(i), which provides confirmation of crystallographi c data. Lattice water is not found in these crystals. The effect of lo w temperature on librational modes of coordinated water and their latt ice vibrations are studied in the 550-50 cm-1 region. The potential fo rce field constants are calculated for rocking, wagging and twisting l ibrational modes of water at 290 K, 80 K and 60 K. The higher value of the potential constant for the rocking mode from the wagging libratio nal mode shows the in-plane bend of the hydrogen bond in lanthanum sul phate crystals.