High-pressure Raman spectra of deuterated L-alanine crystal

Raman spectra of deuterated L-alanine have been obtained at high-pressure conditions. A phase transition at ~1.5 GPa associated with the splitting of some internal modes and increase of the wavenumber of the external modes was observed. Similarly to the hydrogenated L-alanine crystal, this first transition was related to a symmetry change. Moreover, further modifications of the Raman spectra were observed at 4.4 GPa, which may be associated to conformational changes of the molecule. To give further support to such a hypothesis,neutron powder diffraction measurements were performed. Information about the cell parameter at atmospheric pressure gave valuable information about the N-D distances, shedding light on the behavior of the torsional vibration of ND₃ ⁺.