Vibrational spectroscopy at high pressures. Part 31.—Raman and infrared spectra of rubidium and caesium nitrates

Abstract

Mid-infrared and Raman spectra have been obtained for RbNO₃ and CsNO₃ at pressures up to at least 40 kbar in each case and up to 125 kbar for the i.r. spectra of CsNO₃. The data are shown to be consistent with the recently proposed structure for RbNO₃ V based upon the space group Pmmn with z= 2. The clearest evidence comes from the ν₁ and ν₄ regions of the nitrate ion and the libratory lattice mode region. The CsNO₃ III to IV phase transition recently claimed by Kalliomäki and Meisalo on the basis of X-ray measurements has been confirmed but is shown to be extremely sluggish with phase III/IV intergrowths extending over the range 72–109 kbar.