Vibrational Spectra of Ammonium and Other Scheelite-Type Perrhenates.

摘要

The far-infrared and laser-excited Raman spectra of several Scheelite-type perrhenates have been recorded at 77K and room temperature in order to obtain frequencies and symmetry assignments for the lattice modes. Both NH4ReO4were studied to separate ammonium ion translations and librations. At 77K the ammonium ion librational mode is observed at 264/cm in NH4ReO4and 194/cm in ND4ReO4. Upon warming to 300K the ammonium ion librational mode disappears and is unobservable in both the far-IR and Raman spectra. The Raman-active ammonium ion fundamental modes have also been observed in both NH4ReO4and ND4ReO4. The temperature-dependent changes in the intensity and line widths of the ammonium ion fundamentals and lattice modes indicate that the ammonium ion motion undergoes a change between 77K and 300K. (Author)