EXPERIMENTAL The IR and Raman spectra of a single crystal
The crystals were prepared by the slow evaporation of NH 4 Sm(SO 4 ) 2 ؒ 4H 2 O and that of two polycrystalline compounds NH 4 Ln(SO 4 ) 2 ؒ 2H 2 O [Ln ؍ Yb, Tm] have been recorded and an aqueous solution containing lanthanide sulfate and amanalyzed. Two types of SO 4 groups predicted by the X-ray data monium sulfate at room temperature (300 Ϯ 3 K) (4, 5). of the samarium compound are not observed in the present Yb and Tm double sulfate crystals were provided by Dr. study. However, the bands show two crystallographically dis-P. N. Iyer after X-ray diffraction studies. Raman spectra tinct SO 2؊ 4 ions in the other two compounds. The absence of in the Stokes region were recorded using both a Spex 1401 free rotation and broadness of the bands in the internal mode double monochromator and a Dilor Z24 triple monoregion confirms that NH ؉ 4 ions form hydrogen bonds in the chromator with a resolution better than 3 cm Ϫ1 . For excitacrystals under study. The observed stretching and bending tion, the 488-nm line of a Spectra Physics model 165.08 bands show the presence of three distinct types of water moleargon laser with a power of 200 mW was used. Polarized cules in NH 4 Sm(SO 4 ) 2 ؒ 4H 2 O. The water molecules form hydro-Raman spectra of NH 4 Sm(SO 4 ) 2 и 4H 2 O were obtained for gen bonds of medium strength in all three crystals. © 1996 Acathe orientations c(bb)a, c(bc)a, c(ab)a, and c(ac)a. Bedemic Press, Inc.