AbstractPolarized Raman spectra of single crystals of La2(SO4)3, 9H2O and La2(SO4)3, 9D2O have been recorded at room temperature and assignments to the zero wave vector modes proposed. Analysis of the spectra shows the non‐individuality of ions and molecules involved in these crystals and the existence of hydrogen bonds of various lengths. The systemiatc temperature study of Raman spectra shows a singularity in the variation of band intensities in the 273–283 K region which confirms the existence of a phase transition at this temperat