Single crystals of L-valine, C 5 H 11 O 2 N, have been studied by Raman spectroscopy at temperatures from 17 to 300 K over the spectral range 20-3300 cm −1 . A tentative assignment of the bands is given. Careful analysis of the Raman spectra suggests that a series of changes in the low-wavenumber region may be associated with a phase transition undergone by the material, and this possibility is discussed.

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.

Polarized rst-order Raman scattering studies at 300 K were carried out in L -asparagine monohydrate crystal in order to obtain the general assignment of its phonon spectra. A careful analysis of the vibrational spectra shows that the assignment of the fundamental vibrational modes can be done on the basis of amino, carboxilic and water groups vibrations, and correlations with previous data reported for other amino acids. However, some vibrations were correctly assigned from the study of its temperature -dependence behavior performed in the range 10 -300 K. The assignment proposed con rm the zwitterionic structure of L-asparagine monohydrate crystal.

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We report on the strong temperature-dependent thermal expansion, α(D), in CdS quantum dots (QDs) embedded in a glass template. We have performed a systematic study by using the temperature-dependent first-order Raman spectra, in CdS bulk and in dot samples, in order to assess the size dependence of α(D), and where the role of the compressive strain provoked by the glass host matrix on the dot response is discussed. We report the Grüneisen mode parameters and the anharmonic coupling constants for small CdS dots with mean radius R ∼ 2.0 nm. We found that γ parameters change, with respect to the bulk CdS, in a range between 20 and 50%, while the anharmonicity contribution from two-phonon decay channel becomes the most important process to the temperature-shift properties.

Polarized Raman and infrared spectra of l-threonine crystals have been obtained at room temperature and an assignment of normal modes is proposed based on group theory analysis. The usefulness of these assignments comes from the fact that some modes are related to important vibrations that can show c hanges under di erent pressure and temperature conditions.

Polarized Raman spectra of monohydrated L-asparagine (C 4 N 2 O 3 H 8 ·H 2 O) 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.

Polarized Raman spectra of L-arginine hydrochloride monohydrated single crystal in nine different scattering geometries of the two irreducible representations of factor group C 2 were studied at room temperature. The experimental wavenumber values are compared with those obtained from ab-initio calculation and the assignment of the Raman bands to the respective molecular vibrations is also given. Finally, a discussion related to a previously reported phase transition undergone by L-arginine hydrochloride monohydrated single crystal at low temperature is furnished.