The far infrared spectrum of the rare earth double nitrates has been investigated at 300ᐤK, 77ᐤK, and 15ᐤK. Some electronic transitions between the Stark levels of the ground state and a number of vibrational lines have been observed.

It is shown that while the major groupings of the crystal field levels in the optical spectra of the double nitrates may be understood by assuming the crystal field symmetry about the rare earth ion is icosahedral, the structure within these groups can be explained by assuming an approximate symmetry of Tₕ with a small distortion to C₃.

The vibration spectrum of the double nitrates has also been investigated, and it is apparent that most of the lines observed in the Raman and far infrared spectrum may be explained by assuming the transitions take place between levels with the wavevector q = 0.