Raman spectrum of triglycine selenate (G3 Se), [(NH2 CH2 COOH)3 H2 SeO4 ]

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5. Summary

The Raman spectrum of a single crystal of triglycine selenate G3Se which is ferroelectric below 22° C. has been photographed usingλ 2537 excitation. 42 Raman lines have been recorded of which 6 belong to the lattice spectrum, 3 are due to NH...O oscillations and the remaining 33 are due to internal oscillations of the ions of glycine and SeO 4 −− . There is a close similarity between the spectrum of triglycine selenate and the spectrum of its isomorph, triglycine sulphate, the frequency shifts due to the SO 4 −− ion being replaced by the frequency shifts due to the SeO 4 −− ion. The existence of glycine in the zwitterion form in the structure of G3Se is substantiated by the appearance in the Raman spectrum of lines which are attributable to NH 3 + groups and COO groups. The appearance of the additional C-H line at 2982 cm.−1 in the spectrum of triglycine selenate which is absent in the spectrum ofα-glycine indicates the existence of planar monoprotonated glycine also in the structure, as indicated by X-ray studies.