Raman spectrum of triglycine selenate (G₃Se), [(NH₂CH₂COOH)₃ H₂SeO₄]

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.