OPTICALLY ACTIVE CRYSTAL VIBRATIONS OF ALKALI-METAL NITRATES

The infrared and Raman spectra for the three alkali-metal nitrates LiNO3, NaNO3, and KNO3 have been measured in the region from 1600 to 30 wavenumbers, and a normal-coordinate analysis has been made for these compounds with a special emphasis on the rotational and translational lattice modes in the crystal. All three compounds were studied as D3d6 models and a modified Urey-Bradley force field was used in the calculations. The intramolecular and interaction force constants for all three nitrates are given. The effect of the interaction potential constants on the NO3- ion is discussed as well as the effect of the metal ion-nitrate ionic interaction in the crystal from a comparison of the calculated force constants. Although there are large changes in the rotational and translational lattice frequencies when comparing one alkali-metal nitrate with another, the lack of force constant dependence is interesting.