Low-temperature Raman spectra of monohydratedL-asparagine crystals

Polarized Raman spectra of monohydrated L-asparagine (C4N2O3H8·H2O) were studied at temperatures ranging from 300 to 10 K. The wavenumbers of most modes were found to increase linearly upon cooling, although some bands showed an exponential behaviour, which is discussed in terms of anharmonicities of vibrations associated with hydrogen bonds. Evidence was found of a structural phase transition at low temperature by analysis of the external mode region of the spectra. An x-ray diffraction investigation confirmed the occurrence of a structural change between 140 and 150 K. Copyright © 2004 John Wiley & Sons, Ltd.