Abstract
The temperature dependence of the O (H,D) − stretching modes (frequencies, halfwidths, IR, Raman) of polymorphic RbOH and CsOH is studied in terms of hydrogen bonding, disorder of hydroxide ions, and phase transitions. The different ν OD frequencies of isotopically dilue samples (RbOH mon. I and CsOH o-rh. II) in the IR and Raman spectra and the unusually large positive temperature shifts of these bands are interpreted as due to order—disorder transitions from hydrogen-bnded OH − ions in the low-temperature polymorphs to non-H-bonded ions in the room temperature modifications. The halfwidths of the O (H,D) − bands exhibit an Arrhenius type behaviour. In the deuterated compounds there are stronger hydrogen bonds (D-bonds) than in the non-deuterated samples (H-bonds). These findings are attributed to the greater hydrogen bond acceptor strength of OD − than that of OH −. In KBr discs, hitherto unknown isostructural hydroxide bromides of caesium and rubidium are formed.
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