High pressure Raman spectra of L‐methionine crystal

Raman spectra of an L ‐methionine (C₅H₁₁NO₂S) crystal were obtained in the spectral region between 50 and 3200 cm⁻¹ for pressures up to 5 GPa. Pronounced changes of the Raman spectra were observed for bands associated to rocking of CO₂⁻; wagging of CO₂⁻; deformations of CO₂⁻, CH₃, and NH₃⁺; and stretching vibrations of SC, CC, CH, CH₂, and CH₃. Upon decompression to ambient pressure the original Raman spectrum prior to compression is recovered. These modifications were associated to a reversible phase transition undergone by the L ‐methionine crystal at about 2.2 GPa, with a hysteresis of ∼0.8 GPa. Pressure coefficients for most of the internal modes of the crystal are given. Copyright © 2008 John Wiley & Sons, Ltd.