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

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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.