Terahertz Spectroscopy of Crystalline and Non-Crystalline Solids

Parrott, Edward P. J.; Fischer, Bernd; Gladden, Lynn F.; Zeitler, J. Axel; Jepsen, Peter Uhd

doi:10.1007/978-3-642-29564-5_8

Cited by 9 publications

(10 citation statements)

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“…Further information on how to take scattering effects into account and how the optical properties can be extracted accurately from time-domain waveforms has been described in detail elsewhere. [35][36][37][38] Low-Frequency Raman Spectroscopy. Raman spectroscopy was first observed by Raman and Krishnan in 1928 and is based on the interaction of light with the molecular vibrations and phonons of the target system.…”

Section: Techniquesmentioning

confidence: 99%

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Terahertz Time-Domain and Low-Frequency Raman Spectroscopy of Organic Materials

2015

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With the ongoing proliferation of terahertz time-domain instrumentation from semiconductor physics into applied spectroscopy over the past decade, measurements at terahertz frequencies (1 THz [ 10 12 Hz [ 33 cm À1) have attracted a sustained growing interest, in particular the investigation of hydrogen-bonding interactions in organic materials. More recently, the availability of Raman spectrometers that are readily able to measure in the equivalent spectral region very close to the elastic scattering background has also grown significantly. This development has led to renewed efforts in performing spectroscopy at the interface between dielectric relaxation phenomena and vibrational spectroscopy. In this review, we briefly outline the underlying technology, the physical phenomena governing the light-matter interaction at terahertz frequencies, recent examples of spectroscopic studies, and the current state of the art in assigning spectral features to vibrational modes based on computational techniques.

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Section: Techniquesmentioning

confidence: 99%

Section: Techniquesmentioning

confidence: 99%

Terahertz Time-Domain and Low-Frequency Raman Spectroscopy of Organic Materials

2015

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“…The IR and Raman spectra in the low-frequency region (200–10 cm −1 ) derive from the collective translation, libration, and deformations of the molecular skeleton within the crystal lattice. 11 This provides a second fingerprint region that is correlated with the crystal structure of the molecule because lattice phonons are involved. The advent of terahertz (THz) pulsed spectroscopy has facilitated the routine measurement of high-quality FIR spectra, which are typically reported in terahertz rather than wavenumbers.…”

Section: Introductionmentioning

confidence: 99%

“…The advent of terahertz (THz) pulsed spectroscopy has facilitated the routine measurement of high-quality FIR spectra, which are typically reported in terahertz rather than wavenumbers. 11 Raman spectroscopy has also benefitted from recent improvements in technology that facilitate low-frequency Raman measurements. 12 New advances in ultra-narrow-band notch filter technology with volume holographic gratings enable the generation of high-quality, low-frequency Raman spectra using a relatively compact, easy-to-use, and cost-effective system.…”

Section: Introductionmentioning

confidence: 99%

Polymorph Characterization of Active Pharmaceutical Ingredients (APIs) Using Low-Frequency Raman Spectroscopy

et al. 2014

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Polymorph detection, identification, and quantitation in crystalline materials are of great importance to the pharmaceutical industry. Vibrational spectroscopic techniques used for this purpose include Fourier transform mid-infrared (FT-MIR) spectroscopy, Fourier transform near-infrared (FT-NIR) spectroscopy, Raman spectroscopy, and terahertz (THz) and far-infrared (FIR) spectroscopy. Typically, the fundamental molecular vibrations accessed using high-frequency Raman and MIR spectroscopy or the overtone and combination of bands in the NIR spectra are used to monitor the solid-state forms of active pharmaceutical ingredients (APIs). The local environmental sensitivity of the fundamental molecular vibrations provides an indirect probe of the long-range order in molecular crystals. However, low-frequency vibrational spectroscopy provides access to the lattice vibrations of molecular crystals and, hence, has the potential to more directly probe intermolecular interactions in the solid state. Recent advances in filter technology enable high-quality, low-frequency Raman spectra to be acquired using a single-stage spectrograph. This innovation enables the cost-effective collection of high-quality Raman spectra in the 200-10 cm(-1) region. In this study, we demonstrate the potential of low-frequency Raman spectroscopy for the polymorphic characterization of APIs. This approach provides several benefits over existing techniques, including ease of sampling and more intense, information-rich band structures that can potentially discriminate among crystalline forms. An improved understanding of the relationship between the crystalline structure and the low-frequency vibrational spectrum is needed for the more widespread use of the technique.

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“…At THz frequencies, Mie scattering can occur for particles or pore sizes >100 μm where the THz pulse undergoes a significant change in refractive index at the grain boundaries. A good overview of the effects of scattering contributions to THz spectra and an example how Mie scattering can lead to strong apparent absorption features was recently provided by Parrott et al13…”

Section: Resultsmentioning

confidence: 99%