High-pressure Raman study of L-alanine crystal
  Pressure-dependent Raman scattering studies in the range 0.0 -- 32 kbar were carried out in L-alanine in order to investigate its external mode phonon spectra in relation to the phase transitions in the crystal. A careful analysis of the spectra shows that the low-energy Raman modes exhibit variation both in frequency and in intensity and between 26 and 28 kbar it is observed a splitting of a external mode, indicating that the D_2 normal phase undergoes a transition. Pressure coefficients for external modes are also given. 
A. M. R. Teixeira, P. T. C. Freire, A. J. D. Moreno, J. M. Sasaki, A.   P. Ayala, J. Mendes Filho, F. E. A. Melo