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The infrared and Raman spectra of anhydrous crystalline Li2CO3 and Na2CO3 were measured at 300 and at 80°K. Bands observed in the vibrational spectra of Li2CO3 were assigned according to the C2h factor group symmetry. The doublet structure observed for each of the internal modes in the spectra of Na2CO3 was interpreted in terms of an ordered arrangement of CO3= ions over two nonequivalent orientations within the primitive cell. Multiple internal reflection and polarized specular reflectance techniques were used to determine transverse optical (TO) and longitudinal optical (LO) mode frequencies in Li2CO3 and Na2CO3. It was shown from these measurements that the infrared transmission spectra of these compounds exhibit band maxima which are admixtures of LO and TO modes.
Brooker et al. (Tue,) studied this question.
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