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Pressure‐induced phase transitions in L‐leucine crystal
Author(s) -
Façanha Filho P. F.,
Freire P. T. C.,
Melo F. E. A.,
Lemos V.,
Mendes Filho J.,
Pizani P. S.,
Rossatto D. Z.
Publication year - 2009
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.2071
Subject(s) - raman spectroscopy , wavenumber , chemistry , ambient pressure , hydrogen bond , anomaly (physics) , leucine , crystal (programming language) , crystal structure , crystallography , phase transition , lattice (music) , spectral line , internal pressure , phase (matter) , amino acid , condensed matter physics , molecule , thermodynamics , physics , optics , organic chemistry , biochemistry , astronomy , computer science , acoustics , programming language
Raman spectra of a crystal of L ‐leucine, an essential amino acid, were obtained for pressures between 0 and 6 GPa. The results show anomalies at three pressure values, one between 0 and 0.46 GPa, another between 0.8 and 1.46 GPa, and a third at P ∼ 3.6 GPa. The first two anomalies are characterized by the disappearance of lattice modes (which can indicate occurrence of phase transitions), the appearance of several internal modes, or the splitting of modes of high wavenumbers. The changes of internal modes are related to CH and CH 3 unit motions as well as hydrogen bonds, as can be inferred from the behavior of bands associated with CO 2 − moieties. The third anomaly is a discrete change of the slopes of the wavenumber versus pressure plots for most modes observed. Further, decompression to ambient pressure generates the original Raman spectrum, showing that the pressure‐induced anomalies undergone by L ‐leucine crystals are reversible. Copyright © 2008 John Wiley & Sons, Ltd.