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The infrared spectra of crystalline calcium and sodium formates Charlton, Thomas Laurie


The infrared absorption spectra of single crystals of calcium and sodium formate have been recorded between 4OOO and 500 cm⁻¹. With the aid of polarized radiation it was possible to carry out an analysis of the spectra. Factor group splitting was observed for the molecular modes of calcium formate. It was possible to assign the origin of the components of any given molecular fundamental to one of the two sets of symmetrically non-equivalent formate ions in the Calcium formate unit cell. This assignment was made on the basis of the relative Intensities of the components of the fundamentals. For the sodium formate single crystal spectrum, a combination of factor group and site group analysis was required to satisfactorily interpret the results. The results obtained in this case helped to resolve the controversy surrounding the assignment of the √₂ and √₅ molecular modes for the formate ion. Lattice mode frequencies of 36, 61, 90, 128, 154 and 192 cm⁻¹ for calcium formate and 58, 91, 112, 128 and 231 cm⁻¹ for sodium formate are inferred from combinations with molecular modes. The analysis was completed by the assignment of several modes to formate ion fundamentals and to combination and overtone modes of molecular fundamentals.

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