Vibrational studies of molybdates, tungstates and related compounds-I. New infrared data and assignments for the scheelite-type compounds XIIMoO4 and XIIWO4

New experimental data lead to revised assignments for the i.r. frequencies of molybdates and tungstates of the scheelite family. The investigation of isotopic species reveals non-negligible interactions between the internal bending modes and the external translational modes, and allows an easy discrimination between translational and rotational modes. As a consequence, the low-frequency band of these compounds must be assigned to a rotation, and not to a translation as previously assumed. © 1972.