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Issue 24, 2011
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Terahertz spectroscopy of enantiopure and racemic polycrystalline valine

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Abstract

Experimental and computational THz (or far-infrared) spectra of polycrystalline valine samples are reported. The experimental spectra have been measured using THz time-domain spectroscopy. Spectra of the pure enantiomers, both D and L, as well as the DL racemate have been taken at room temperature and low temperature (78 K). The spectra of the pure D and L enantiomers are essentially identical, and they are markedly different from the DL racemate. In addition, a temperature-dependent study of L-valine was undertaken in which the absorption maxima were found to red shift as a function of increasing temperature. The vibrational absorption spectra (frequencies and intensities) were calculated using the harmonic approximation with the Perdew–Burke–Ernzerhof (PBE) functional, localized atomic orbital basis sets, and periodic boundary conditions. The calculated and experimental spectra are in good qualitative agreement. A general method of quantifying the degree to which a calculated mode is intermolecular versus intramolecular is demonstrated, with the intermolecular motions further separated into translational versus rotational/librational motion. This allows straightforward comparison of spectra calculated using different basis sets or other constraints.

Graphical abstract: Terahertz spectroscopy of enantiopure and racemic polycrystalline valine

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Publication details

The article was received on 02 Mar 2011, accepted on 28 Apr 2011 and first published on 20 May 2011


Article type: Paper
DOI: 10.1039/C1CP20594C
Citation: Phys. Chem. Chem. Phys., 2011,13, 11719-11730
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    Terahertz spectroscopy of enantiopure and racemic polycrystalline valine

    M. R. C. Williams, A. B. True, A. F. Izmaylov, T. A. French, K. Schroeck and C. A. Schmuttenmaer, Phys. Chem. Chem. Phys., 2011, 13, 11719
    DOI: 10.1039/C1CP20594C

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