Raman Spectra of Tetragonal KH2PO4

Raman spectra of crystalline K${\mathrm{H}}_2$P${\mathrm{O}}_4$ at 294 °K are reported for shifts up to 700 ${\mathrm{cm}}^{-1\mathrm{}}$. Five of the six optical-phonon modes of the ${\mathrm{K}}^{+}$-${\left({\mathrm{H}}_2\mathrm{P}{\mathrm{O}}_4\right)}^{-}$ lattice are unequivocally identified; their positions and linewidths are accurately determined. Analysis of the spectral structures above 300 ${\mathrm{cm}}^{-1\mathrm{}}$ shows that the tetrahedral ${\left(\mathrm{P}{\mathrm{O}}_4\right)}^{3-}$ ion remains essentially as an "individual" molecule in the crystal, and its vibrational modes are split by the local crystalline field of $S_4$ symmetry.