Étude vibrationnelle de LaS2, PrS2 et NdS2

We have carried out an infrared and Raman spetroscopic study of light rare earth polysulphides LnS 2 with cubic (Pr, Nd), tetragonal (Ce), orthorhombic (La) and monoclinic (La) symmetry. The cubic, tetragonal and monoclinic phases have nearly identical spectra. Analysis of the infrared and Raman spectra of orthorhombic LaS 2 leads us to propose the non-centrosymmetric space group Pn2 1 a for this compound, rather than Pnma as previously suggested in the literature