Raman Spectra of Solid (NH4)2CrO4and (ND4)2CrO4Obtained by a Rotating Cell Technique

Abstract

The Raman spectra of polycrystalline (NH4)2CrO4and (ND4)2CrO4have been obtained by a sample rotation technique where the uncompressed solid is contained in a glass cylindrical cell. The apparatus is a commerically available sample rotator for liquids, which was modified for the described solid sampling technique. The Raman spectra of (NH4)2CrO4and (ND4)2CrO4are discussed in relation to their uniquely monoclinic structure, in contrast to the β-K2SO4structure found for (NH4)2SO4and many alkali metal chromates and sulfates. The hydrogen bonding in (NH4)2CrO4is described, and its role in determining both the structure and the Raman spectra is discussed. The data suggest a barrier to NH4+rotation of approximately 3.70 kcal/mol, indicating that the ammonium ions are not freely rotating on the time scale of the Raman experiment (10−13sec).