Dependence of low frequency spectra on solute and solvent in solutions studied by terahertz time-domain spectroscopy

Dissociation and Recombination Processes in Lactose Monohydrate Detected by THz Time-Domain Spectroscopy

The terahertz (THz) region has much appeal for differentiating between hydrate systems and for physically characterizing pharmaceutical drug materials. The present study employs THz absorption spectroscopy to investigate the effect of heating on dehydration and hydration in α-lactose monohydrate. Distinctive THz absorption spectra were observed following various heating durations. The THz absorption spectra for α-lactose monohydrate and anhydrous α-lactose exhibit clear differences. Pure α-lactose monohydrate displays clear absorption peaks at 0.53, 1.05, 1.11, 1.33, and 1.56 THz. The complete dehydration of α-lactose monohydrate takes only 15 mins at 145°C (418 K). Moreover, the THz refractive index of α-lactose monohydrate decreases during dehydration. The dehydration of α-lactose monohydrate was also studied using Beer–Lambert law to compare THz absorption spectra as functions of the heating time. The absorption coefficient spectra recorded at 0.53 and 1.35 THz for α-lactose monohydrate after different dehydration times vary linearly with the remaining water content.

Terahertz time-domain and low-frequency Raman spectroscopy of organic materials

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(-1)) 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.