High pressure Raman spectra of β-form of l-glutamic acid

Raman spectroscopy was used to investigate the vibrational properties of l-glutamic acid in the β-form in a diamond-anvil cell up to pressures of 21.5 GPa in the spectral region between 20 and 3270 cm−1. From the analysis of the results it was observed that the crystal undergoes an impressive series of phase transitions in this pressure range. The phase transitions are accompanied by modifications in a number of modes and discontinuities in the wavenumber versus pressure plots, as well as by modifications in the bands associated to both rocking and stretching modes of NH3+. Upon decompression to ambient pressure the original spectra were recovered indicating that the phase transitions are reversible.