RAMAN-SPECTRUM OF CARBONATES MIICO3 IN THE 1100-1000 CM-1 REGION - OBSERVATION OF THE NU-1 MODE OF THE ISOTOPIC ((CO2O)-O-16-O-18)2- ION

The Raman spectrum of a series of carbonates M(II)CO3 with aragonite or calcite structure has been reinvestigated in the 1100-1000 cm-1 region, corresponding to the totally symmetric stretch (v1) of the (CO3)2- anion. Besides the very strong peak corresponding to the v1 mode of the ((CO3)2-)-O-16 ion. nearly all spectra exhibit a very weak satellite peak whose frequency agrees well with the calculated v1 frequency of the isotopic ion ((CO2O)2-)-O-16-O-18. Small deviations from the theoretical values are qualitatively discussed on the basis of vibrational couplings between near-neighbour anions.