Polarized Raman spectra and intermolecular potential of α-glycine-C-d2 and DL-alanine-α,β-d4 crystals

Polarized Raman spectra of α-glycine-C-d2 and DL-alanine-α,β-d4 single crystals have been measured. Large factor group splittings due to the non-bonded atom–atom interaction were observed for the CD2 bending mode of glycine-C-d2 and the CD3 asymmetric deformation and the CD3 torsional modes of DL-alanine-α,β-d4. These factor group splittings and their change on N-deuteration were explained fairly well by a normal coordinate analysis with an intermolecular potential of the exp-6 type for the non-bonded atom–atom interaction for the H…H, C…H, C…C and O…H(C) pairs. Good agreement was obtained between the observed and the calculated lattice frequencies on addition of the N…O non-bonded interaction potential, the hydrogen bond stretching terms and the Coulomb interaction terms to the intermolecular potential.