Vibrational spectra of alkali hydrogen selenites,selenous acid,and their deuterated analogs

The infrared and Raman spectra of alkali hydrogen selenites (MHSeO₃), where M = Li, Na, K, or Cs], selenous acid (H₂Seo₃), and their deuterated analogs have been recorded and interpreted. The internal mode frequencies observed in sodium hydrogen selenite, selenous acid, and sodium trihydrogen selenite are used to generate general valence force constants for HSeO^?₃ and H₂SeO₃ under the assumption of C_s geometry for each species. Calculations of observed deuterium frequency shifts are made to aid in the assignments of the various internal modes. A low-temperature proton-triggered phase transition is observed in CsHSeO₃ and is confirmed in KHSeO₃. A discussion of the effects of proton order and disorder upon the selenite frequencies is also presented.