Raman spectroscopy of l-phenylalanine nitric acid submitted to high pressure☆

In the present work we show a systematic investigation on vibrational properties of l-phenylalanine nitric acid [2C9H11NO2·H+·NO3−] single crystal obtained by the slow evaporation method at room temperature. We have characterized the l-phenylalanine nitric acid crystal by means of both the Fourier transform infrared spectroscopy in the spectral range between 400cm−1 to 4000cm−1 and Fourier transform Raman spectroscopy in the spectral range from 50cm−1 to 3500cm−1. We also report results of high-pressure Raman scattering measurements in the range of 0.0–7.0GPa. The data are consistent with the hypothesis that the crystal undergoes a phase transition at about 0.6GPa, where it is observed the disappearance of phonons in the external mode region of the spectrum and changes of bands associated with both NH3+ rocking and CH2 rocking vibrations.