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.

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Single‐crystal samples of taurine, NH3C2H4SO3, were studied by Raman spectroscopy in a diamond‐anvil cell up to pressures of 5.6 GPa. From the analysis of the results we observed that the crystal undergoes a phase transition at about 0.7 GPa. The transition is accompanied by the appearance of a phonon in the external mode region of the spectrum and by changes of both the wavenumber of the CCN bending and of the CSH torsional vibrations. Additionally evidence for a second phase transition occurring at 5.2 GPa was observed. Pressure coefficients for all modes observed in this work are also given. Copyright © 2001 John Wiley & Sons, Ltd.

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