Infrared and Raman spectrum of CaU04: a new data and interpretations

New Raman and i.r. data on CaU04, including isotopic and solid solutions frequencies, are presented and interpreted with the support of a group theoretical analysis and a normal coordinate treatment. The oxygen atoms only are allowed to move during the four Raman-active modes, all of which have been observed. The vibrational behaviour of the Casub(1-x)Srsub(x)U04 solid solutions suggest that two of these modes are conveniently described by internal motions of the uranyl group, viz. symmetric stretch (696 cm-1) and librational (340 cm-1) motions. Similarly, solid solution frequencies and 40Ca-44Ca isotopic shifts lead to a satisfactory assignment of the five observed (against six predicted) i.r. frequencies: internal motions of the uranyl ion (696 and 366 cm-1 for the antisymmetric stretching, and bending respectively), translations of the Ca++ ion (305 and 165-1), and translation of the oxygen (435 cm-1). Most of these assignments do not agree with those previously proposed. The non-reproducibility of some i.r. frequencies is also discussed. (author)