Optical properties and the crystal structure of anhydrous gadolinium-trichloride

The Raman and i.r. reflection spectra of GdCl3 have been studied in order to estabish the optically active fundamental frequencies. Gd3+−Cl−)-and (Cl−−Cl−)-force constants in GdCl3 and in LaCl3 and PrCl3 have been calculated on the basis of a simple rigid ion model. It is found that the apparently anomalous spectra of GdCl3 may be a result of a stronger (Cl−−Cl−)-coupling constant than in the hexagonal rare earth trichlorides with lower Z on the metal ion. This peculiar status of GdCl3 is related to the change of crystal structure in the series of Rare-Earth trichlorides from a hexagonal (La-…Gd-) Cl3 to an orthorhombic (TbCl3 DyCl3) structure. Some properties of the electronic spectra are also discussed in this context.