Raman spectroscopy and inelastic neutron scattering study of crystalline L-valine

Information about the strength of the hydrogen bond interactions in crystalline L-valine was obtained by Raman and inelastic neutron scattering spectroscopies. Raman studies were carried out from room temperature up to 423 K in order to examine both the external and the internal vibrations in L-valine. The structure seems to be stable above room temperature since no indication of a phase transition or clear indication of reorientation of L-valine molecules was observed. From the inelastic neutron scattering measurements, made between 270 and 320 K, for fully hydrogenated and partially deuterated L-valine, a better description of the low frequency modes was possible. Moreover it was possible to establish that the phase transition at low temperatures is related to the activation of an infrared mode in the Raman spectra. Additionally the low temperature phase of L-valine was further characterized by means of specific heat measurements between 5 and 350 K.