FIR absorption studies of neodymium sulphate by FTIR at low temperatures

Far infrared (FIR) spectra of neodymium sulphate octahydrate and its deuterated analogue crystals were studied in the 400-50 cm⁻¹ region. Measurements were carried out at ambient and low temperatures. A quasi structure model was used to identify the absorption bands and for the assignment of the spectral information. Bands pertaining to librational modes hindered rotations, and translation modes arising from different molecular groups, ions and bondings were obtained. Low temperature measurements were quite useful for revealing the removal of degeneracy, sharpening of the bands, shifting of the frequency and in the identification of weak bands. Deuteration of the crystals was used to identify the bands pertaining to water molecules present in the lattice and in the coordinated water. The isotopic shift arising from the corresponding bands of H₂O and D₂O was found to be 1.053 at a temperature of 290 K and 1.043 at 60 K.