The internal vibrations of the ammonium ion in (ND4)(2) TeCl6 have bee
n studied by Raman scattering in the temperature range 4.2-300 K. Spli
tting of A(1)-, E-, and T-2- modes have been observed at T-c2 = 48 K a
nd T-c5 = 28 K. These splittings were well interpreted by group theore
tical correlation method. The reason for the transitions at T-c2 and T
-c5 may be the decrease of the force constant in the deuterated ammoni
um ion.